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76-442: Taurine ( / ˈ t ɔː r iː n / ), or 2-aminoethanesulfonic acid , is a non-proteinogenic naturally occurring amino sulfonic acid that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine , and accounts for up to 0.1% of total human body weight. Taurine is named after Latin taurus ( cognate to Ancient Greek ταῦρος, taûros ) meaning bull or ox , as it

152-528: A chick , as in William Shakespeare 's play Macbeth , where Macduff laments the death of "all my pretty chickens and their dam". The usage is preserved in placenames such as the Hen and Chicken Islands . In older sources, and still often in trade and scientific contexts, chickens as a species are described as common fowl or domestic fowl . Chickens are relatively large birds , active by day . The body

228-521: A mutation that causes extra feathering under the face, giving the appearance of a beard. Chickens are omnivores . In the wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards , small snakes, and young mice . A chicken may live for 5–10 years, depending on the breed . The world's oldest known chicken lived for 16 years. Chickens are gregarious , living in flocks , and incubate eggs and raise young communally. Individual chickens dominate others, establishing

304-412: A pecking order ; dominant individuals take priority for access to food and nest sites. The concept of dominance, involving pecking, was described in female chickens by Thorleif Schjelderup-Ebbe in 1921 as the "pecking order". Male chickens tend to leap and use their claws in conflicts. Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox. A male's crowing

380-460: A zwitterion H 3 NCH 2 CH 2 SO − 3 , as verified by X-ray crystallography . The sulfonic acid has a low p K a ensuring that it is fully ionized to the sulfonate at the pHs found in the intestinal tract. Synthetic taurine is obtained by the ammonolysis of isethionic acid (2-hydroxyethanesulfonic acid), which in turn is obtained from the reaction of ethylene oxide with aqueous sodium bisulfite . A direct approach involves

456-458: A decline in GnRH-I-N. Hens often try to lay in nests that already contain eggs and sometimes move eggs from neighbouring nests into their own. A flock thus uses only a few preferred locations, rather than having a different nest for every bird. Under natural conditions, most birds lay only until a clutch is complete; they then incubate all the eggs. This is called "going broody ". The hen sits on

532-622: A dedicated codon, but are added in place of a stop codon when a specific sequence is present, UGA codon and SECIS element for selenocysteine, UAG PYLIS downstream sequence for pyrrolysine. All other amino acids are termed "non-proteinogenic". There are various groups of amino acids: These groups overlap, but are not identical. All 22 proteinogenic amino acids are biosynthesised by organisms and some, but not all, of them also are abiotic (found in prebiotic experiments and meteorites). Some natural amino acids, such as norleucine , are misincorporated translationally into proteins due to infidelity of

608-494: A diet lacking in this essential amino acid are dilated cardiomyopathy , and reproductive failure in female cats. Decreased plasma taurine concentration has been demonstrated to be associated with feline dilated cardiomyopathy . Unlike CRD, the condition is reversible with supplementation. Taurine is now a requirement of the Association of American Feed Control Officials (AAFCO) and any dry or wet food product labeled approved by

684-493: A family of golden retrievers suffering from taurine deficiency treatable with supplementation. Foxes on fur farms also appear to require dietary taurine. The rhesus , cebus and cynomolgus monkeys each require taurine at least in infancy. The giant anteater also requires taurine. Taurine appears to be essential for the development of passerine birds. Many passerines seek out taurine-rich spiders to feed their young, particularly just after hatching. Researchers compared

760-426: A gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl ( G. sonneratii ). It is estimated that chickens share between 71 and 79% of their genome with red junglefowl. According to one early study, a single domestication event of the red junglefowl in present-day Thailand gave rise to the modern chicken with minor transitions separating the modern breeds. The red junglefowl

836-507: A greater affinity for oxygen, binding oxygen more readily. Fertile chicken eggs hatch at the end of the incubation period, about 21 days; the chick uses its egg tooth to break out of the shell. Hens remain on the nest for about two days after the first chick hatches; during this time the newly hatched chicks feed by absorbing the internal yolk sac . The hen guards her chicks and broods them to keep them warm. She leads them to food and water and calls them towards food. The chicks imprint on

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912-467: A hen (a circle dance), often lowering the wing which is closest to the hen. The dance triggers a response in the hen and when she responds to his call, the rooster may mount the hen and proceed with the mating. Mating typically involves a sequence in which the male approaches the female and performs a waltzing display. If the female is unreceptive, she runs off; otherwise, she crouches, and the male mounts, treading with both feet on her back. After copulation

988-746: A mosaic of divergent ancestries inherited from subspecies of red junglefowl. A word for the domestic chicken ( *manuk ) is part of the reconstructed Proto-Austronesian language , indicating they were domesticated by the Austronesian peoples since ancient times. Chickens, together with dogs and pigs, were carried throughout the entire range of the prehistoric Austronesian maritime migrations to Island Southeast Asia , Micronesia , Island Melanesia , Polynesia , and Madagascar , starting from at least 3000 BC from Taiwan . These chickens might have been introduced during pre-Columbian times to South America via Polynesian seafarers, but evidence for this

1064-646: A sacred rooster, often during a ritual cockfight , used as a form of communication with the gods. In Gabriel García Márquez 's Nobel-Prize-winning 1967 novel One Hundred Years Of Solitude , cockfighting is outlawed in the town of Macondo after the patriarch of the Buendia family murders his cockfighting rival and is haunted by the man's ghost. Chicken jokes have been made at least since The Knickerbocker published one in 1847. Chickens have been featured in art in farmyard scenes such as Adriaen van Utrecht 's 1646 Turkeys and Chickens and Walter Osborne 's 1885 Feeding

1140-478: A single domestication event of red junglefowl whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar. These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups. Analysis of the most popular commercial breed shows that the White Leghorn breed possesses

1216-406: A thioether bond and is found in various organisms. Similarly, djenkolic acid , a plant toxin from jengkol beans , is composed of two cysteines connected by a methylene group. Diaminopimelic acid is both used as a bridge in peptidoglycan and is used a precursor to lysine (via its decarboxylation). In meteorites and in prebiotic experiments (e.g. Miller–Urey experiment ) many more amino acids than

1292-557: A vector for bacterial diseases such as salmonellosis and spirochaetosis . Viral diseases include avian influenza . Chickens are common and widespread domestic animals, with a total population of 23.7 billion as of 2018 . More than 50 billion chickens are reared annually as a source of meat and eggs. In the United States alone, more than 8 billion chickens are slaughtered each year for meat, and more than 300 million chickens are reared for egg production. The vast majority of poultry

1368-539: Is "considered to be a skin and eye irritant and skin sensitiser, and to be hazardous if inhaled;" it may be safe to consume up to 6 grams of taurine per day. Other sources indicate that taurine is safe for supplemental intake in normal healthy adults at up to 3 grams per day. A 2008 review found no documented reports of negative or positive health effects associated with the amount of taurine used in energy drinks, concluding, "The amounts of guarana , taurine, and ginseng found in popular energy drinks are far below

1444-611: Is a contest held in a ring called a cockpit between two cocks. Cockfighting is outlawed in many countries as involving cruelty to animals . The activity seems to have been practised in the Indus Valley civilisation from 2500 to 2100 BC. In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used for food. Chickens have long been used as model organisms to study developing embryos. Large numbers of embryos can be provided commercially; fertilized eggs can easily be opened and used to observe

1520-604: Is a large and round short-winged bird , domesticated from the red junglefowl of Southeast Asia around 8,000 years ago. Most chickens are raised for food, providing meat and eggs ; others are kept as pets or for cockfighting . Chickens are common and widespread domestic animals, with a total population of 26.5 billion as of 2023 , and an annual production of more than 50 billion birds. A hen bred for laying can produce over 300 eggs per year. There are numerous cultural references to chickens in folklore, religion, and literature. Terms for chickens include: Chicken can mean

1596-409: Is a loud and sometimes shrill call, serving as a territorial signal to other males, and in response to sudden disturbances within their surroundings. Hens cluck loudly after laying an egg and to call their chicks. Chickens give different warning calls to indicate that a predator is approaching from the air or on the ground. To initiate courting, some roosters may dance in a circle around or near

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1672-418: Is also produced by the transsulfuration pathway , which converts homocysteine into cystathionine . The cystathionine is then converted to hypotaurine by the sequential action of three enzymes: cystathionine gamma-lyase , cysteine dioxygenase , and cysteine sulfinic acid decarboxylase. Hypotaurine is then oxidized to taurine as described above. A pathway for taurine biosynthesis from serine and sulfate

1748-416: Is amidated with a cephalosporin moiety. Penicillamine is a therapeutic amino acid, whose mode of action is unknown. Naturally-occurring cyanotoxins can also include non-proteinogenic amino acids. Microcystin and nodularin , for example, are both derived from ADDA , a β-amino acid. Taurine is an amino sulfonic acid and not an amino carboxylic acid, however it is occasionally considered as such as

1824-677: Is an amino acid. The proteinogenic amino acids are a small subset of this group that possess a central carbon atom (α- or 2-) bearing an amino group, a carboxyl group, a side chain and an α-hydrogen levo conformation , with the exception of glycine , which is achiral , and proline , whose amine group is a secondary amine and is consequently frequently referred to as an imino acid for traditional reasons, albeit not an imino. The genetic code encodes 20 standard amino acids for incorporation into proteins during translation . However, there are two extra proteinogenic amino acids: selenocysteine and pyrrolysine . These non-standard amino acids do not have

1900-444: Is an ingredient in some energy drinks in amounts of 1–3 g per serving. A 1999 assessment of European consumption of energy drinks found that taurine intake was 40–400 mg per day. Taurine is not regarded as an essential human dietary nutrient and has not been assigned recommended intake levels. High-quality clinical studies to determine possible effects of taurine in the body or following dietary supplementation are absent from

1976-407: Is commonly sold as a dietary supplement , but there is no good clinical evidence that taurine supplements provide any benefit to human health. Taurine is used as a food additive for cats (who require it as an essential nutrient), dogs, and poultry. Taurine concentrations in land plants are low or undetectable, but up to 1000 nmol/g wet weight have been found in algae . Taurine exists as

2052-430: Is conditional, differing by species and growth stage. The Olive flounder , for example, has lower capacity to synthesize taurine compared to the rainbow trout . Juvenile fish are less efficient at taurine biosyntheis due to reduced cysteine sulfinate decarboxylase levels. Non-proteinogenic amino acids Technically, any organic compound with an amine (–NH 2 ) and a carboxylic acid (–COOH) functional group

2128-592: Is inhumane towards sentient animals . Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment. Chickens farmed for meat are called broilers . Broiler breeds typically take less than six weeks to reach slaughter size, some weeks longer for free range and organic broilers. Chickens farmed primarily for eggs are called layer hens. The UK alone consumes more than 34 million eggs per day. Hens of some breeds can produce over 300 eggs per year;

2204-452: Is naturally derived from cysteine . Mammalian taurine synthesis occurs in the liver via the cysteine sulfinic acid pathway. In this pathway, cysteine is first oxidized to its sulfinic acid, catalyzed by the enzyme cysteine dioxygenase . Cysteine sulfinic acid, in turn, is decarboxylated by sulfinoalanine decarboxylase to form hypotaurine . Hypotaurine is enzymatically oxidized to yield taurine by hypotaurine dehydrogenase . Taurine

2280-460: Is only one standard amino acid with a straight chain, alanine, could simply be redundancy with valine, leucine and isoleucine. However, straight chained amino acids are reported to form much more stable alpha helices. Serine, homoserine , O -methylhomoserine and O -ethylhomoserine possess a hydroxymethyl, hydroxyethyl, O -methylhydroxymethyl and O -methylhydroxyethyl side chain; whereas cysteine, homocysteine , methionine and ethionine possess

2356-468: Is raised in factory farms . According to the Worldwatch Institute , 74% of the world's poultry meat and 68% of eggs are produced this way. An alternative to intensive poultry farming is free-range farming. Friction between these two main methods has led to long-term issues of ethical consumerism . Opponents of intensive farming argue that it harms the environment, creates human health risks and

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2432-414: Is reported in microalgae , developing chicken embryos , and chick liver . Serine dehydratase converts serine to 2-aminoacrylate , which is converted to cysteic acid by 3′-phosphoadenylyl sulfate :2-aminoacrylate C - sulfotransferase . Cysteic acid is converted to taurine by cysteine sulfinic acid decarboxylase . Taurine occurs naturally in fish and meat. The mean daily intake from omnivore diets

2508-489: Is round, the legs are unfeathered in most breeds, and the wings are short. Wild junglefowl can fly ; chickens and their flight muscles are too heavy to allow them to fly more than a short distance. Size and coloration vary widely between breeds. Adult chickens of both sexes have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin on either side under their beaks called wattles ; combs and wattles are more prominent in males . Some breeds have

2584-678: Is still putative. The possibility that domestic chickens were in the Americas before Western contact is debated by researchers, but blue-egged chickens, found only in the Americas and Asia, suggest an Asian origin for early American chickens. A lack of data from Thailand, Russia, the Indian subcontinent, Southeast Asia and Sub-Saharan Africa makes it difficult to lay out a clear map of the spread of chickens in these areas; better description and genetic analysis of local breeds threatened by extinction may also help with research into this area. Chicken bones from

2660-513: Is supplemented by mentions in historical texts from the last few centuries BC, and by depictions in prehistoric artworks, such as across Central Asia. Chickens were widespread throughout southern Central Asia by the 4th century BC. Middle Eastern chicken remains go back to a little earlier than 2000 BC in Syria . Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. During

2736-452: Is that the former is racemised by a PLP -binding enzymes (encoded by alr or the homologue dadX ), whereas the latter is racemised by a cofactor independent enzyme ( murI ). Some variants are present, in Thermotoga spp. D -Lysine is present and in certain vancomycin -resistant bacteria D -serine is present ( vanT gene). All proteinogenic amino acids have at least one hydrogen on

2812-426: Is well adapted to take advantage of the vast quantities of seed produced during the end of the multi-decade bamboo seeding cycle , to boost its own reproduction. In domesticating the chicken, humans took advantage of the red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply. Exactly when and where the chicken was domesticated remains controversial. Genomic studies estimate that

2888-540: The Arauco Peninsula in south-central Chile were radiocarbon dated as pre-Columbian, and DNA analysis suggested they were related to prehistoric populations in Polynesia. However, further study of the same bones cast doubt on the findings. Chicken remains have been difficult to date, given the small and fragile bird bones; this may account for discrepancies in dates given by different sources. Archaeological evidence

2964-631: The Galliformes , the order of bird that chickens belong to, survived the Cretaceous–Paleogene extinction event that killed all tree-dwelling birds and their dinosaur relatives. Chickens are descended primarily from the red junglefowl ( Gallus gallus ) and are scientifically classified as the same species. Domesticated chickens freely interbreed with populations of red junglefowl. The domestic chicken has subsequently hybridised with grey junglefowl , Sri Lankan junglefowl and green junglefowl ;

3040-609: The Hellenistic period (4th–2nd centuries BC), in the southern Levant , chickens began to be widely domesticated for food. The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BC. Breeding increased under the Roman Empire and reduced in the Middle Ages . Genetic sequencing of chicken bones from archaeological sites in Europe revealed that in

3116-751: The High Middle Ages chickens became less aggressive and began to lay eggs earlier in the breeding season. Chickens reached Egypt via the Middle East for purposes of cockfighting about 1400 BC and became widely bred in Egypt around 300 BC. Three possible routes of introduction into Africa around the early first millennium AD could have been through the Egyptian Nile Valley, the East Africa Roman-Greek or Indian trade, or from Carthage and

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3192-452: The IUPAC numbering system to differentiate the various carbons in an organic molecule, by sequentially assigning a number to each carbon, including those forming a carboxylic group, the carbons along the side-chain of amino acids can also be labelled with Greek letters, where the α-carbon is the central chiral carbon possessing a carboxyl group, a side chain and, in α-amino acids, an amino group –

3268-459: The AAFCO should have a minimum of 0.1% taurine in dry food and 0.2% in wet food. Studies suggest the amino acid should be supplied at 10 mg per kilogram of bodyweight per day for domestic cats. A number of other mammals also have a requirement for taurine. While the majority of dogs can synthesize taurine, case reports have described a singular American cocker spaniel , 19 Newfoundland dogs , and

3344-524: The Berbers, across the Sahara . The earliest known remains are from Mali , Nubia , East Coast, and South Africa and date back to the middle of the first millennium AD. Chickens are susceptible both to parasites such as mites , and to diseases caused by pathogens such as bacteria and viruses . The parasite Dermanyssus gallinae feeds on blood, causing irritation and reducing egg production, and acts as

3420-479: The UK and Europe, laying hens are then slaughtered and used in processed foods, or sold as 'soup hens'. In some other countries, flocks are sometimes force moulted rather than being slaughtered to re-invigorate egg-laying. This involves complete withdrawal of food (and sometimes water) for 7–14 days or sufficiently long to cause a body weight loss of 25 to 35%, or up to 28 days under experimental conditions. This stimulates

3496-493: The amino acid molecule. Thus a β-amino acid has the amine group bonded to the second carbon away, and a γ-amino acid has it on the third. Examples include β-alanine , GABA , and δ- aminolevulinic acid . The reason why α-amino acids are used in proteins has been linked to their frequency in meteorites and prebiotic experiments. An initial speculation on the deleterious properties of β-amino acids in terms of secondary structure turned out to be incorrect. Some amino acids contain

3572-419: The amounts expected to deliver either therapeutic benefits or adverse events". Cats lack the enzymatic machinery ( sulfinoalanine decarboxylase ) to produce taurine and must therefore acquire it from their diet. A taurine deficiency in cats can lead to retinal degeneration and eventually blindness – a condition known as central retinal degeneration as well as hair loss and tooth decay. Other effects of

3648-423: The amounts required to suppress the auxotroph in certain organisms (such as cats) are closer to those of "essential amino acids" (amino acid auxotrophy) than of vitamins (cofactor auxotrophy). The osmolytes, sarcosine and glycine betaine are derived from amino acids, but have a secondary and quaternary amine respectively. Chicken Gallus domesticus L. The chicken ( Gallus domesticus )

3724-604: The behaviours and development of birds fed a taurine-supplemented diet to a control diet and found the juveniles fed taurine-rich diets as neonates were much larger risk takers and more adept at spatial learning tasks. Under natural conditions, each blue tit nestling receive 1 mg of taurine per day from parents. Taurine can be synthesized by chickens. Supplementation has no effect on chickens raised under adequate lab conditions, but seems to help with growth under stresses such as heat and dense housing. Species of fish, mostly carnivorous ones, show reduced growth and survival when

3800-448: The carbon in carboxylic groups is not counted. (Consequently, the IUPAC names of many non-proteinogenic α-amino acids start with 2-amino- and end in -ic acid .) Most natural amino acids are α-amino acids in the L configuration, but some exceptions exist. Some non-α-amino acids exist in organisms. In these structures, the amine group is displaced further from the carboxylic acid end of

3876-456: The catalytic flexibility of PLP-binding enzymes, many amino acids are synthesised as keto acids (such as 4-methyl-2-oxopentanoate to leucine) and aminated in the last step, thus keeping the number of non-proteinogenic amino acid intermediates fairly low. Ornithine and citrulline occur in the urea cycle , part of amino acid catabolism (see below). In addition to primary metabolism , several non-proteinogenic amino acids are precursors or

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3952-425: The chicken genome is similarly sized compared to other birds, but smaller than nearly all mammals: the human genome is 3.2 Gb . The final gene set contained 26,640 genes (including noncoding genes and pseudogenes ), with a total of 19,119 protein-coding genes, a similar number to the human genome. In 2006, scientists researching the ancestry of birds switched on a chicken recessive gene , talpid2 , and found that

4028-456: The chicken was domesticated 8,000 years ago in Southeast Asia and spread to China and India 2,000 to 3,000 years later. Archaeological evidence supports domestic chickens in Southeast Asia well before 6000 BC, China by 6000 BC and India by 2000 BC. A landmark 2020 Nature study that fully sequenced 863 chickens across the world suggests that all domestic chickens originate from

4104-446: The developing embryo. Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development. For instance, many important discoveries in limb development have been made using chicken embryos, such as the discovery of the apical ectodermal ridge and the zone of polarizing activity . The chicken was the first bird species to have its genome sequenced. At 1.21 Gb ,

4180-406: The embryo jaws initiated formation of teeth, like those found in ancient bird fossils. Chickens are featured widely in folklore , religion , literature , and popular culture. The chicken is a sacred animal in many cultures and deeply embedded in belief systems and religious practices. Roosters are sometimes used for divination , a practice called alectryomancy. This involves the sacrifice of

4256-439: The final production in secondary metabolism to make small compounds or non-ribosomal peptides (such as some toxins ). Despite not being encoded by the genetic code as proteinogenic amino acids, some non-standard amino acids are nevertheless found in proteins. These are formed by post-translational modification of the side chains of standard amino acids present in the target protein. These modifications are often essential for

4332-404: The fish-based feed in their food is replaced with soy meal or feather meal. Taurine has been identified as the factor responsible for this phenomenon; supplementation of taurine to plant-based fish feed reverses these effects. Future aquaculture is expected to use more of these more environmentally-friendly protein sources, so supplementation would become more important. The need of taurine in fish

4408-445: The function or regulation of a protein; for example, in γ-carboxyglutamate the carboxylation of glutamate allows for better binding of calcium cations , and in hydroxyproline the hydroxylation of proline is critical for maintaining connective tissues . Another example is the formation of hypusine in the translation initiation factor EIF5A , through modification of a lysine residue. Such modifications can also determine

4484-490: The hen and subsequently follow her continually. She continues to care for them until they are several weeks old. Inbreeding of White Leghorn chickens tends to cause inbreeding depression expressed as reduced egg number and delayed sexual maturity. Strongly inbred Langshan chickens display obvious inbreeding depression in reproduction, particularly for traits such as age when the first egg is laid and egg number. Water or ground-dwelling fowl similar to modern partridges , in

4560-949: The hen to lose her feathers but also re-invigorates egg-production. Some flocks may be force-moulted several times. In 2003, more than 75% of all flocks were moulted in the US. Keeping chickens as pets became increasingly popular in the 2000s among urban and suburban residents. Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs. Chickens provide companionship and have individual personalities. While many do not cuddle much, they will eat from one's hand, jump onto one's lap, respond to and follow their handlers, as well as show affection. Chickens are social, inquisitive, intelligent birds, and many people find their behaviour entertaining. Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities. A cockfight

4636-418: The highest authenticated rate of egg laying is 371 eggs in 364 days. After 12 months of laying, the commercial hen's egg-laying ability declines to the point where the flock is commercially unviable. Hens, particularly from battery cage systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from around seven years to less than two years. In

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4712-471: The literature. Preliminary human studies on the possible effects of taurine supplementation have been inadequate due to low subject numbers, inconsistent designs, and variable doses. Preliminary studies have suggested that supplementing with taurine may increase exercise capacity and affects lipid profiles in individuals with diabetes. According to the European Food Safety Authority , taurine

4788-711: The localization of the protein, for example, the addition of long hydrophobic groups can cause a protein to bind to a phospholipid membrane. There is some preliminary evidence that aminomalonic acid may be present, possibly by misincorporation, in protein. Several non-proteinogenic amino acids are toxic due to their ability to mimic certain properties of proteinogenic amino acids, such as thialysine . Some non-proteinogenic amino acids are neurotoxic by mimicking amino acids used as neurotransmitters (that is, not for protein biosynthesis), including quisqualic acid , canavanine and azetidine-2-carboxylic acid . Cephalosporin C has an α-aminoadipic acid (homoglutamate) backbone that

4864-614: The male does a tail-bending display. Sperm transfer occurs by cloacal contact between the male and female, in an action called the 'cloacal kiss'. As with all birds, reproduction is controlled by a neuroendocrine system, the Gonadotropin-Releasing Hormone-I neurons in the hypothalamus . Reproductive hormones including estrogen , progesterone , and gonadotropins ( luteinizing hormone and follicle-stimulating hormone ) initiate and maintain sexual maturation changes. Reproduction declines with age, thought to be due to

4940-492: The metallic flavor of potassium chloride , a salt substitute. Prematurely born infants are believed to lack the enzymes needed to convert cystathionine to cysteine , and may, therefore, become deficient in taurine. Taurine is present in breast milk , and has been added to many infant formulas as a measure of prudence since the early 1980s. However, this practice has never been rigorously studied, and as such it has yet to be proven to be necessary, or even beneficial. Taurine

5016-462: The nest, fluffing up or pecking defensively if disturbed. She rarely leaves the nest until the eggs have hatched. Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments. When eggs are placed in a hypoxic environment, chicken embryos from these populations express much more hemoglobin than embryos from other chicken populations. This hemoglobin has

5092-463: The opposite absolute chirality, chemicals that are not available from normal ribosomal translation and transcription machinery. Most bacterial cells walls are formed by peptidoglycan , a polymer composed of amino sugars crosslinked with short oligopeptides bridged between each other. The oligopeptide is non-ribosomally synthesised and contains several peculiarities including D-amino acids , generally D -alanine and D -glutamate. A further peculiarity

5168-550: The protein-synthesis process. Many amino acids, such as ornithine , are metabolic intermediates produced biosynthetically, but not incorporated translationally into proteins. Post-translational modification of amino acid residues in proteins leads to the formation of many proteinaceous, but non-proteinogenic, amino acids. Other amino acids are solely found in abiotic mixes (e.g. α-methylnorvaline). Over 30 unnatural amino acids have been inserted translationally into protein in engineered systems, yet are not biosynthetic. In addition to

5244-405: The protein. Two crosslinked cysteines form a cystine molecule. Cysteine and methionine are generally produced by direct sulfurylation, but in some species they can be produced by transsulfuration , where the activated homoserine or serine is fused to a cysteine or homocysteine forming cystathionine . A similar compound is lanthionine , which can be seen as two alanine molecules joined via

5320-503: The reaction of aziridine with sulfurous acid . In 1993, about 5000–6000  tonnes of taurine were produced for commercial purposes: 50% for pet food and 50% in pharmaceutical applications. As of 2010, China alone has more than 40 manufacturers of taurine. Most of these enterprises employ the ethanolamine method to produce a total annual production of about 3000  tonnes. In the laboratory, taurine can be produced by alkylation of ammonia with bromoethanesulfonate salts. Taurine

5396-543: The thiol equivalents. The selenol equivalents are selenocysteine, selenohomocysteine, selenomethionine and selenoethionine. Amino acids with the next chalcogen down are also found in nature: several species such as Aspergillus fumigatus , Aspergillus terreus , and Penicillium chrysogenum in the absence of sulfur are able to produce and incorporate into protein tellurocysteine and telluromethionine. In cells, especially autotrophs, several non-proteinogenic amino acids are found as metabolic intermediates. However, despite

5472-408: The twenty standard amino acids are found, several of which are at higher concentrations than the standard ones. It has been conjectured that if amino acid based life were to arise elsewhere in the universe, no more than 75% of the amino acids would be in common. The most notable anomaly is the lack of aminobutyric acid. The genetic code has been described as a frozen accident and the reasons why there

5548-437: The α-carbon instead of a hydrogen. It is therefore achiral. Another compound similar to alanine without an α-hydrogen is dehydroalanine , which possess a methylene sidechain. It is one of several naturally occurring dehydroamino acids . A subset of L -α-amino acids are ambiguous as to which of two ends is the α-carbon. In proteins a cysteine residue can form a disulfide bond with another cysteine residue, thus crosslinking

5624-422: The α-carbon. Glycine has two hydrogens, and all others have one hydrogen and one side-chain. Replacement of the remaining hydrogen with a larger substituent, such as a methyl group, distorts the protein backbone. In some fungi α-aminoisobutyric acid is produced as a precursor to peptides, some of which exhibit antibiotic properties. This compound is similar to alanine, but possesses an additional methyl group on

5700-557: Was determined to be around 58 mg (range 9–372 mg ), and to be low or negligible from a vegan diet. Typical taurine consumption in the American diet is about 123–178 mg per day. Taurine is partially destroyed by heat in processes such as baking and boiling. This is a concern for cat food, as cats have a dietary requirement for taurine and can easily become deficient. Either raw feeding or supplementing taurine can satisfy this requirement. Both lysine and taurine can mask

5776-456: Was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin . It was discovered in human bile in 1846 by Edmund Ronalds . Although taurine is abundant in human organs with diverse putative roles, it is not an essential human dietary nutrient and is not included among nutrients with a recommended intake level . Taurine is synthesized naturally in the human liver from methionine and cysteine . Taurine

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