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47-440: Like all other amino acids, aspartic acid contains an amino group and a carboxylic acid. Its α-amino group is in the protonated –NH 3 form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO under physiological conditions. Aspartic acid has an acidic side chain (CH 2 COOH) which reacts with other amino acids, enzymes and proteins in the body. Under physiological conditions (pH 7.4) in proteins

94-469: A supplement of an individual amino acid (methionine, lysine, threonine, or tryptophan) can be added to the feed. Protein content in foods is often measured in protein per serving rather than protein per calorie. For instance, the USDA lists 6 grams of protein per large whole egg (a 50-gram serving) rather than 84 mg of protein per calorie (71 calories total). For comparison, there are 2.8 grams of protein in

141-484: A body. A positive balance occurs when more nitrogen is consumed than is excreted, which indicates that some of the nitrogen is being used by the body to build proteins. A negative nitrogen balance occurs when more nitrogen is excreted than is consumed, which indicates that there is insufficient intake for the body to maintain its health. Graduate students at the University of Illinois were fed an artificial diet so that there

188-439: A day to have a healthy protein profile, and almost 6 kg to get enough calories. It is recommended that adult humans obtain between 10–35% of their 2000 calories a day as protein. Scientists had known since the early 20th century that rats could not survive on a diet whose only protein source was zein , which comes from maize (corn), but recovered if they were fed casein from cow's milk. This led William Cumming Rose to

235-408: A diet containing no protein and the nitrogen losses recorded. During the first week or more there is a rapid loss of labile proteins. Once the nitrogen losses stabilize, this baseline is determined to be the minimum required for maintenance. Then the test subjects were fed a measured amount of the food being tested. The difference between the nitrogen in that food and the nitrogen losses above baseline

282-409: A hydrogen acceptor in a chain of ATP synthase. Dietary L-aspartic acid has been shown to act as an inhibitor of Beta-glucuronidase , which serves to regulate enterohepatic circulation of bilirubin and bile acids. Click on genes, proteins and metabolites below to link to respective articles. Aspartate (the conjugate base of aspartic acid) stimulates NMDA receptors , though not as strongly as

329-421: A mixture of two. Of these two forms, only one, " L -aspartic acid", is directly incorporated into proteins. The biological roles of its counterpart, " D -aspartic acid" are more limited. Where enzymatic synthesis will produce one or the other, most chemical syntheses will produce both forms, " DL -aspartic acid", known as a racemic mixture . In the human body, aspartate is most frequently synthesized through

376-579: A serving of raw broccoli (100 grams) or 82 mg of protein per calorie (34 calories total), or the Daily Value of 47.67g of protein after eating 1,690g of raw broccoli a day at 574 cal. An egg contains 12.5g of protein per 100g, but 4 mg more protein per calorie, or the protein DV after 381g of egg, which is 545 cal. The ratio of essential amino acids (the quality of protein) is not taken into account, one would actually need to eat more than 3 kg of broccoli

423-505: Is biodegradable superabsorbent polymers (SAP), and hydrogels. Around 75% of superabsorbent polymers are used in disposable diapers and an additional 20% is used for adult incontinence and feminine hygiene products. Polyaspartic acid , the polymerization product of aspartic acid, is a biodegradable substitute to polyacrylate . In addition to SAP, aspartic acid has applications in the fertilizer industry , where polyaspartate improves water retention and nitrogen uptake. Aspartic acid

470-431: Is 10% to 20% higher than adult levels and those for infants can be as much as 150% higher in the first year of life. Cysteine (or sulfur-containing amino acids), tyrosine (or aromatic amino acids), and arginine are always required by infants and growing children. Methionine and cysteine are grouped together because one of them can be synthesized from the other using the enzyme methionine S -methyltransferase and

517-426: Is a metabolite in the urea cycle and participates in gluconeogenesis . It carries reducing equivalents in the malate-aspartate shuttle , which utilizes the ready interconversion of aspartate and oxaloacetate , which is the oxidized (dehydrogenated) derivative of malic acid . Aspartate donates one nitrogen atom in the biosynthesis of inosine , the precursor to the purine bases. In addition, aspartic acid acts as

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564-435: Is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms, the nine amino acids humans cannot synthesize are valine , isoleucine , leucine , methionine , phenylalanine , tryptophan , threonine , histidine , and lysine . Six other amino acids are considered conditionally essential in

611-691: Is classified as an acidic amino acid, with a pK a of 3.9; however, in a peptide this is highly dependent on the local environment, and could be as high as 14. The one-letter code D for aspartate was assigned arbitrarily, with the proposed mnemonic aspar D ic acid. Aspartic acid was first discovered in 1827 by Auguste-Arthur Plisson and Étienne Ossian Henry by hydrolysis of asparagine , which had been isolated from asparagus juice in 1806. Their original method used lead hydroxide , but various other acids or bases are now more commonly used instead. There are two forms or enantiomers of aspartic acid. The name "aspartic acid" can refer to either enantiomer or

658-487: Is not an essential amino acid , which means that it can be synthesized from central metabolic pathway intermediates in humans, and does not need to be present in the diet. In eukaryotic cells, roughly 1 in 20 amino acids incorporated into a protein is an aspartic acid, and accordingly almost any source of dietary protein will include aspartic acid. Additionally, aspartic acid is found in: Essential amino acid An essential amino acid , or indispensable amino acid ,

705-410: Is reabsorbed by the small intestine, conjugated bilirubin is not reabsorbed in small intestine. All conjugated bilirubin in the large intestine is metabolised by colonic bacteria to urobilinogen , which is then further oxidized to urobilin and stercobilin . Urobilin, stercobilin and their degradation products give feces its brown color. However, just like bile, some of the urobilinogen reabsorbed

752-514: Is resecreted in the bile which is also part of enterohepatic circulation. The rest of the reabsorbed urobilinogen is excreted in the urine where it is converted to an oxidized form, urobilin , which gives urine its characteristic yellow color. Chloramphenicol , aspirin , paracetamol , diazepam , lorazepam , morphine , metronidazole . Not only drugs but also endogenous substrates like bilirubin, steroidal hormones and thyroxine utilize this pathway. Enterohepatic circulation of drugs describes

799-429: Is reused about 20 times, often multiple times during a single digestive phase. The presence of biliary acids in the intestines helps in absorption of fats and other substances. Bilirubin is conjugated with glucuronic acid in the liver by the enzyme glucuronyltransferase , making it soluble in water. Much of it goes into the bile and thus out into the small intestine. Although 20% of the secreted bilirubinoid bile

846-448: Is somewhat unclear, as some amino acids can be produced from others. The sulfur -containing amino acids, methionine and homocysteine , can be converted into each other but neither can be synthesized de novo in humans. Likewise, cysteine can be made from homocysteine but cannot be synthesized on its own. So, for convenience, sulfur-containing amino acids are sometimes considered a single pool of nutritionally equivalent amino acids as are

893-411: Is synthesized by the urea cycle to meet the needs of an adult but perhaps not those of a growing child. Amino acids that must be obtained from the diet are called essential amino acids . Eukaryotes can synthesize some of the amino acids from other substrates . Consequently, only a subset of the amino acids used in protein synthesis are essential nutrients . Nonessential amino acids are produced in

940-405: Is synthesized from NH 4 and glutamate, and asparagine is synthesized similarly. Proline and arginine are both derived from glutamate. Serine , formed from 3-phosphoglycerate , which comes from glycolysis , is the precursor of glycine and cysteine . Tyrosine is synthesized by the hydroxylation of phenylalanine , which is an essential amino acid. Estimating the daily requirement for

987-482: Is the precursor to several amino acids, including four that are essential for humans: methionine , threonine , isoleucine , and lysine . The conversion of aspartate to these other amino acids begins with reduction of aspartate to its "semialdehyde", O 2 CCH(NH 2 )CH 2 CHO. Asparagine is derived from aspartate via transamidation: (where G C(O)NH 2 and G C(O)OH are glutamine and glutamic acid , respectively) Aspartate has many other biochemical roles. It

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1034-426: The aromatic amino acid pair, phenylalanine and tyrosine . Likewise arginine , ornithine , and citrulline , which are interconvertible by the urea cycle , are considered a single group. If one of the essential amino acids is not available in the required quantities, protein synthesis will be inhibited, irrespective of the availability of the other amino acids. Protein deficiency has been shown to affect all of

1081-635: The liver to the bile , followed by entry into the small intestine , absorption by the enterocyte and transport back to the liver. Enterohepatic circulation is an especially important concept in the field of toxicology as many lipophilic xenobiotics undergo this process causing repeated liver damage. Hepatocytes metabolize cholesterol to cholic acid and chenodeoxycholic acid . These lipid - soluble bile acids are conjugated (reversibly attached) mainly to glycine or taurine molecules to form water soluble primary conjugated bile acids, sometimes called "bile salts". These bile acids travel to

1128-522: The transamination of oxaloacetate . The biosynthesis of aspartate is facilitated by an aminotransferase enzyme: the transfer of an amine group from another molecule such as alanine or glutamine yields aspartate and an alpha-keto acid. Industrially, aspartate is produced by amination of fumarate catalyzed by L- aspartate ammonia-lyase . Racemic aspartic acid can be synthesized from diethyl sodium phthalimidomalonate, (C 6 H 4 (CO) 2 NC(CO 2 Et) 2 ). In plants and microorganisms , aspartate

1175-550: The "quality" or "value" of various kinds of protein. Measures include the biological value , net protein utilization , protein efficiency ratio , protein digestibility corrected amino acid score and the complete proteins concept. These concepts are important in the livestock industry , because the relative lack of one or more of the essential amino acids in animal feeds would have a limiting effect on growth and thus on feed conversion ratio . Thus, various feedstuffs may be fed in combination to increase net protein utilization, or

1222-502: The 21st amino acid). Pyrrolysine (considered the 22nd amino acid), which is proteinogenic only in certain microorganisms, is not used by and therefore non-essential for most organisms, including humans. The limiting amino acid is the essential amino acid which is furthest from meeting nutritional requirements. This concept is important when determining the selection, number, and amount of foods to consume because even when total protein and all other essential amino acids are satisfied if

1269-459: The actual amino acid content of foods. The USDA used this technique in their own labs to determine the content of 7793 foods across 28 categories. The USDA published the final database in 2018 to the public. The limiting amino acid depends on the human requirements and there are currently two sets of human requirements from authoritative sources: one published by WHO and the other published by USDA . Various attempts have been made to express

1316-474: The amino acid neurotransmitter L-glutamate does. In 2014, the global market for aspartic acid was 39.3 thousand short tons (35.7 thousand tonnes ) or about $ 117 million annually. The three largest market segments include the U.S., Western Europe, and China. Current applications include biodegradable polymers ( polyaspartic acid ), low calorie sweeteners ( aspartame ), scale and corrosion inhibitors, and resins. One area of aspartic acid market growth

1363-427: The amino acids arginine , cysteine , glutamine , glycine , proline and tyrosine are considered conditionally essential , which means that specific populations who do not synthesize it in adequate amounts, such as newborn infants and people with diseased livers who are unable to synthesize cysteine, must obtain one or more of these conditionally essential amino acids from their diet. For example, enough arginine

1410-653: The body's organs and many of its systems, for example affecting brain development in infants and young children; inhibiting upkeep of the immune system, increasing risk of infection; affecting gut mucosal function and permeability, thereby reducing absorption and increasing vulnerability to systemic disease ; and impacting kidney function. The physical signs of protein deficiency include edema , failure to thrive in infants and children, poor musculature, dull skin, and thin and fragile hair. Biochemical changes reflecting protein deficiency include low serum albumin and low serum transferrin . The amino acids that are essential in

1457-466: The body. The pathways for the synthesis of nonessential amino acids come from basic metabolic pathways. Glutamate dehydrogenase catalyzes the reductive amination of α-ketoglutarate to glutamate . A transamination reaction takes place in the synthesis of most amino acids. At this step, the chirality of the amino acid is established. Alanine and aspartate are synthesized by the transamination of pyruvate and oxaloacetate , respectively. Glutamine

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1504-420: The catalyst methionine synthase . Phenylalanine and tyrosine are grouped together because tyrosine can be synthesized from phenylalanine using the enzyme phenylalanine hydroxylase . Historically, amino acid requirements were determined by calculating the balance between dietary nitrogen intake and nitrogen excreted in the liquid and solid wastes, because proteins represent the largest nitrogen content in

1551-401: The conjugated bile acids which remained un-ionized conjugated bile acids are passively absorbed. Venous blood from the ileum goes straight into the portal vein and then into the liver sinusoids . There, hepatocytes extract bile acids very efficiently, and little escapes the healthy liver into systemic circulation. The net effect of enterohepatic recirculation is that each bile salt molecule

1598-585: The discovery of the essential amino acid threonine . Through manipulation of rodent diets, Rose was able to show that ten amino acids are essential for rats: lysine , tryptophan , histidine , phenylalanine , leucine , isoleucine , methionine , valine , and arginine , in addition to threonine. Rose's later work showed that eight amino acids are essential for adult human beings, with histidine also being essential for infants. Longer-term studies established histidine as also essential for adult humans. The distinction between essential and non-essential amino acids

1645-555: The finding that there is no difference in the diets of children developing marasmus as opposed to kwashiorkor. Still, for instance in Dietary Reference Intakes (DRI) maintained by the USDA , lack of one or more of the essential amino acids is described as protein-energy malnutrition . Enterohepatic circulation Enterohepatic circulation is the circulation of biliary acids , bilirubin , drugs or other substances from

1692-468: The gall bladder during the interdigestive phase for storage and to the descending part of the duodenum via the common bile duct through the major duodenal papilla during digestion. 95% of the bile acids which are delivered to the duodenum will be recycled by the enterohepatic circulation. Due to the pH of the small intestine, most of the bile acids are ionized and mostly occur as their sodium salts which are then called “primary conjugated bile salts.” In

1739-486: The human diet were established in a series of experiments led by William Cumming Rose . The experiments involved elemental diets to healthy male graduate students. These diets consisted of corn starch , sucrose , butterfat without protein, corn oil , inorganic salts, the known vitamins , a large brown "candy" made of liver extract flavored with peppermint oil (to supply any unknown vitamins), and mixtures of highly purified individual amino acids. The main outcome measure

1786-518: The human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. These six are arginine , cysteine , glycine , glutamine , proline , and tyrosine . Six amino acids are non-essential ( dispensable ) in humans, meaning they can be synthesized in sufficient quantities in the body. These six are alanine , aspartic acid , asparagine , glutamic acid , serine , and selenocysteine (considered

1833-406: The indispensable amino acids has proven to be difficult; these numbers have undergone considerable revision over the last 20 years. The following table lists the recommended daily amounts currently in use for essential amino acids in adult humans (unless specified otherwise), together with their standard one-letter abbreviations. The recommended daily intakes for children aged three years and older

1880-501: The intestine (e.g. irinotecan ), these molecules which would not otherwise be very toxic can become so because of this process, and therefore inhibition of this step can be protective. For the majority of drugs which undergo enterohepatic circulation that are not toxic to the intestine, inhibition of this process leads to a reduction of the levels of drug and reduced therapeutic effect. For example, antibiotics that kill gut bacteria often reduce enterohepatic drug circulation and this requires

1927-464: The limiting amino acid is not satisfied then the meal is considered to be nutritionally limited by that amino acid. (*) Pyrrolysine , sometimes considered the "22nd amino acid", is not used by the human body. Of the twenty amino acids common to all life forms (not counting selenocysteine ), humans cannot synthesize nine: histidine , isoleucine , leucine , lysine , methionine , phenylalanine , threonine , tryptophan and valine . Additionally,

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1974-479: The lower small intestine and colon , bacteria dehydroxylate some of the primary bile salts to form secondary conjugated bile salts (which are still water-soluble). Along the proximal and distal ileum , these conjugated primary bile salts are reabsorbed actively into hepatic portal circulation. Bacteria deconjugate some of the primary and secondary conjugated bile salts back to lipid-soluble bile acids, which are passively absorbed into hepatic portal circulation. Finally,

2021-413: The process by which drugs are conjugated to glucuronic acid in the liver, excreted into bile, metabolized back into the free drug by intestinal bacteria, and the drug is then reabsorbed into plasma. For many drugs that undergo this process, lower doses of drugs can be therapeutically effective because elimination is reduced by the 'recycling' of the drug. But for a small number of drugs that are very toxic to

2068-465: The side chain usually occurs as the negatively charged aspartate form, −COO. It is a non- essential amino acid in humans, meaning the body can synthesize it as needed. It is encoded by the codons GAU and GAC. In proteins aspartate sidechains are often hydrogen bonded to form asx turns or asx motifs , which frequently occur at the N-termini of alpha helices . Aspartic acid, like glutamic acid ,

2115-537: Was nitrogen balance . Rose noted that the symptoms of nervousness, exhaustion, and dizziness were encountered to a greater or lesser extent whenever human subjects were deprived of an essential amino acid. Essential amino acid deficiency should be distinguished from protein-energy malnutrition , which can manifest as marasmus or kwashiorkor . Kwashiorkor was once attributed to pure protein deficiency in individuals who were consuming enough calories ("sugar baby syndrome"). However, this theory has been challenged by

2162-444: Was a slightly positive nitrogen balance. Then one amino acid was omitted and the nitrogen balance recorded. If a positive balance continued, then that amino acid was deemed not essential. If a negative balance occurred, then that amino acid was slowly restored until a slightly positive nitrogen balance stabilized and the minimum amount recorded. A similar method was used to determine the protein content of foods. Test subjects were fed

2209-402: Was the amount the body retained to rebuild proteins. The amount of nitrogen retained divided by the total nitrogen intake is called net protein utilization . The amount of nitrogen retained divided by the (nitrogen intake minus nitrogen loss above baseline) is called biological value and is usually given as a percentage. Modern techniques make use of ion exchange chromatography to determine

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