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65-639: ACTC may refer to: ACTC1 Stock symbol for Advanced Cell Technology Alameda County Transportation Commission , California, United States All Ceylon Tamil Congress , a Sri Lankan political party representing the Sri Lankan Tamil ethnic minority Andhra Christian Theological College , Hyderabad, India Apple Certified Technical Coordinator Ashland Community and Technical College , Kentucky, United States Asociación Corredores de Turismo Carretera , motorsport governing body Associated Colleges of
130-543: A 40 kDa protein involved in the organization of patches. Plant genome studies have revealed the existence of protein isovariants within the actin family of genes. Within Arabidopsis thaliana , a model organism , there are ten types of actin, six profilins, and dozens of myosins. This diversity is explained by the evolutionary necessity of possessing variants that slightly differ in their temporal and spatial expression. The majority of these proteins were jointly expressed in
195-521: A directed fashion much faster than diffusion. Myosin V walks towards the barbed end of actin filaments, while myosin VI walks toward the pointed end. Most actin filaments are arranged with the barbed end toward the cellular membrane and the pointed end toward the cellular interior. This arrangement allows myosin V to be an effective motor for the export of cargos, and myosin VI to be an effective motor for import. The traditional image of actin's function relates it to
260-427: A filament is formed by monomers in a "sheet" formation, in which the subdomains turn about themselves, this form is also found in the bacterial actin homologue MreB . The terms "pointed" and "barbed" referring to the two ends of the microfilaments derive from their appearance under transmission electron microscopy when samples are examined following a preparation technique called "decoration". This method consists of
325-482: A high degree of evolutionary conservation, along with many signalling molecules. Together these elements allow a spatially and temporally modulated assembly that defines a cell's response to both internal and external stimuli. Yeasts contain three main elements that are associated with actin: patches, cables, and rings. Despite not being present for long, these structures are subject to a dynamic equilibrium due to continual polymerization and depolymerization. They possess
390-600: A length of 23.7 Å. These studies have shown the precise contact points between monomers. Some are formed with units of the same chain, between the "barbed" end on one monomer and the "pointed" end of the next one. While the monomers in adjacent chains make lateral contact through projections from subdomain IV, with the most important projections being those formed by the C-terminus and the hydrophobic link formed by three bodies involving residues 39–42, 201–203, and 286. This model suggests that
455-458: A lid over the central catalytic cavity. Substrates bind to CCT through specific domains. It was initially thought that it only bound with actin and tubulin , although recent immunoprecipitation studies have shown that it interacts with a large number of polypeptides , which possibly function as substrates . It acts through ATP-dependent conformational changes that on occasion require several rounds of liberation and catalysis in order to complete
520-445: A major constituent of the contractile apparatus. The beta and gamma actins coexist in most cell types as components of the cytoskeleton , and as mediators of internal cell motility . It is believed that the diverse range of structures formed by actin enabling it to fulfill such a large range of functions is regulated through the binding of tropomyosin along the filaments. A cell's ability to dynamically form microfilaments provides
585-408: A number of accessory proteins including ADF/cofilin, which has a molecular weight of 16kDa and is coded for by a single gene, called COF1 ; Aip1, a cofilin cofactor that promotes the disassembly of microfilaments; Srv2/CAP, a process regulator related to adenylate cyclase proteins; a profilin with a molecular weight of approximately 14 kDa that is related/associated with actin monomers; and twinfilin,
650-439: A number of cellular activities, such as the cytoplasmic currents generated by the microfilaments and myosin. Actin is also involved in the movement of organelles and in cellular morphogenesis, which involve cell division as well as the elongation and differentiation of the cell. The most notable proteins associated with the actin cytoskeleton in plants include: villin , which belongs to the same family as gelsolin /severin and
715-424: A reaction. In order to successfully complete their folding, both actin and tubulin need to interact with another protein called prefoldin , which is a heterohexameric complex (formed by six distinct subunits), in an interaction that is so specific that the molecules have coevolved . Actin complexes with prefoldin while it is still being formed, when it is approximately 145 amino acids long, specifically those at
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#1732851313112780-445: A regulator of formation and activity of protein complexes such as transcriptional complex. Actin is also involved in cell movement. A meshwork of actin filaments marks the forward edge of a moving cell, and the polymerization of new actin filaments pushes the cell membrane forward in protrusions called lamellipodia . These membrane protrusions then attach to the substrate, forming structures known as focal adhesions that connect to
845-399: A role that is involved in an organism's reaction to stress . Nuclear actin was first noticed and described in 1977 by Clark and Merriam. Authors describe a protein present in the nuclear fraction, obtained from Xenopus laevis oocytes, which shows the same features as skeletal muscle actin. Since that time there have been many scientific reports about the structure and functions of actin in
910-421: A significant effect on its function in nuclear processes, as the level of individual isoforms can be controlled independently. Functions of actin in the nucleus are associated with its ability to polymerize and interact with various ABPs and with structural elements of the nucleus. Nuclear actin is involved in: Due to its ability to undergo conformational changes and interaction with many proteins, actin acts as
975-614: A structural filament (F-actin) in the form of a two-stranded helix . Each actin can bind to four others. The atomic structure of monomeric actin was solved by Kabsch et al., and closely thereafter this same group published the structure of the actin filament. Actins are highly conserved proteins; the alpha actins are found in muscle tissues and are a major constituent of the contractile apparatus. Cardiac (ACTC1) and skeletal ( ACTA1 ) alpha actins differ by only four amino acids ( Asp 4 Glu , Glu 5 Asp , Leu 301 Met , Ser 360 Thr ; cardiac/skeletal). The actin monomer has two asymmetric domains;
1040-463: Is a 40 nanometre long protein that is wrapped around the F-actin helix. During the resting phase the tropomyosin covers the actin's active sites so that the actin-myosin interaction cannot take place and produce muscular contraction. There are other protein molecules bound to the tropomyosin thread, these are the troponins that have three polymers: troponin I , troponin T , and troponin C . F-actin
1105-508: Is able to cut microfilaments and bind actin monomers in the presence of calcium cations; fimbrin , which is able to recognize and unite actin monomers and which is involved in the formation of networks (by a different regulation process from that of animals and yeasts); formins , which are able to act as an F-actin polymerization nucleating agent; myosin , a typical molecular motor that is specific to eukaryotes and which in Arabidopsis thaliana
1170-409: Is both strong and dynamic. Unlike other polymers , such as DNA , whose constituent elements are bound together with covalent bonds , the monomers of actin filaments are assembled by weaker bonds. The lateral bonds with neighbouring monomers resolve this anomaly, which in theory should weaken the structure as they can be broken by thermal agitation. In addition, the weak bonds give the advantage that
1235-516: Is coded for by 17 genes in two distinct classes; CHUP1, which can bind actin and is implicated in the spatial distribution of chloroplasts in the cell; KAM1/MUR3 that define the morphology of the Golgi apparatus as well as the composition of xyloglucans in the cell wall; NtWLIM1, which facilitates the emergence of actin cell structures; and ERD10, which is involved in the association of organelles within membranes and microfilaments and which seems to play
1300-521: Is composed of a β-meander and a β-α-β clockwise unit. It is present in both domains suggesting that the protein arose from gene duplication. Under various conditions, G-actin molecules polymerize into longer threads called "filamentous-" or "F-actin". These F-actin threads are typically composed of two helical strands of actin wound around each other, forming a 7 to 9 nanometer wide helix that repeats every 72 nanometers (or every 14 G-actin subunits). In F-actin threads, G-actin molecules are all oriented in
1365-522: Is composed of actin, myosin, anillin , and α-actinin . In the fission yeast Schizosaccharomyces pombe , actin is actively formed in the constricting ring with the participation of Arp3 , the formin Cdc12, profilin , and WASp , along with preformed microfilaments. Once the ring has been constructed the structure is maintained by a continual assembly and disassembly that, aided by the Arp2/3 complex and formins,
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#17328513131121430-412: Is different from Wikidata All article disambiguation pages All disambiguation pages ACTC1 11464 ENSG00000159251 ENSMUSG00000068614 P68032 P68033 NM_005159 NM_009608 NP_005150 NP_033738 ACTC1 encodes cardiac muscle alpha actin . This isoform differs from the alpha actin that is expressed in skeletal muscle, ACTA1 . Alpha cardiac actin
1495-492: Is extremely abundant in most cells, comprising 1–5% of the total protein mass of most cells, and 10% of muscle cells. The actin protein is found in both the cytoplasm and the cell nucleus . Its location is regulated by cell membrane signal transduction pathways that integrate the stimuli that a cell receives stimulating the restructuring of the actin networks in response. There are a number of different types of actin with slightly different structures and functions. α-actin
1560-525: Is found exclusively in muscle fibres , while β- and γ-actin are found in other cells. As the latter types have a high turnover rate the majority of them are found outside permanent structures. Microfilaments found in cells other than muscle cells are present in three forms: Actin's cytoskeleton is key to the processes of endocytosis , cytokinesis , determination of cell polarity and morphogenesis in yeasts . In addition to relying on actin, these processes involve 20 or 30 associated proteins, which all have
1625-463: Is highly acidic and starts with an acetyled aspartate in its amino group. While its C-terminus is alkaline and is formed by a phenylalanine preceded by a cysteine , which has a degree of functional importance. Both extremes are in close proximity within the I-subdomain. An anomalous N -methylhistidine is located at position 73. The tertiary structure is formed by two domains known as
1690-461: Is key to one of the central processes of cytokinesis. Actin-myosin pairs can also participate in the trafficking of various membrane vesicles and organelles within the cell. Myosin V is activated by binding to various cargo receptors on organelles, and then moves along an actin filament towards the (+) end, pulling its cargo along with it. These nonconventional myosins use ATP hydrolysis to transport cargo, such as vesicles and organelles, in
1755-459: Is required in order to ensure that folding takes place correctly. CCT is a group II chaperonin, a large protein complex that assists in the folding of other proteins. CCT is formed of a double ring of eight different subunits (hetero-octameric) and it differs from group I chaperonins like GroEL , which is found in Eubacteria and in eukaryotic organelles, as it does not require a co-chaperone to act as
1820-405: Is special and almost unique in protein chemistry. The reason for this special route could be the need to avoid the presence of incorrectly folded actin monomers, which could be toxic as they can act as inefficient polymerization terminators. Nevertheless, it is key to establishing the stability of the cytoskeleton, and additionally, it is an essential process for coordinating the cell cycle . CCT
1885-433: Is the monomeric subunit of two types of filaments in cells: microfilaments , one of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. It can be present as either a free monomer called G-actin (globular) or as part of a linear polymer microfilament called F-actin (filamentous), both of which are essential for such important cellular functions as
1950-469: Is the major protein of the thin filament in cardiac sarcomeres, which are responsible for muscle contraction and generation of force to support the pump function of the heart. Cardiac alpha actin is a 42.0 kDa protein composed of 377 amino acids. Cardiac alpha actin is a filamentous protein extending from a complex mesh with cardiac alpha-actinin ( ACTN2 ) at Z-lines towards the center of the sarcomere . Polymerization of globular actin (G-actin) leads to
2015-546: The ACTC1 gene has a role during development. Experiments in chick embryos found an association between ACTC1 knockdown and a reduction in the atrial septa . Polymorphisms in ACTC1 have been linked to dilated cardiomyopathy in a small number of Japanese patients. Further studies in patients from South Africa found no association. The E101K missense mutation has been associated with hypertrophic cardiomyopathy and left ventricular noncompaction . Another mutation has in
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2080-488: The ACTC1 gene has been associated with atrial septal defects . Actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton , and the thin filaments in muscle fibrils . It is found in essentially all eukaryotic cells , where it may be present at a concentration of over 100 μM ; its mass is roughly 42 kDa , with a diameter of 4 to 7 nm. An actin protein
2145-600: The mobility and contraction of cells during cell division . Actin participates in many important cellular processes, including muscle contraction , cell motility , cell division and cytokinesis , vesicle and organelle movement, cell signaling , and the establishment and maintenance of cell junctions and cell shape. Many of these processes are mediated by extensive and intimate interactions of actin with cellular membranes . In vertebrates, three main groups of actin isoforms , alpha , beta , and gamma have been identified. The alpha actins, found in muscle tissues, are
2210-481: The tissue analysed. Actin networks are distributed throughout the cytoplasm of cells that have been cultivated in vitro . There is a concentration of the network around the nucleus that is connected via spokes to the cellular cortex, this network is highly dynamic, with a continuous polymerization and depolymerization. Even though the majority of plant cells have a cell wall that defines their morphology, their microfilaments can generate sufficient force to achieve
2275-444: The "ATPase fold", a structure conserved among ATP and GTP-binding proteins that binds to a magnesium ion and a molecule of ATP. Binding of ATP or ADP is required to stabilize each actin monomer; without one of these molecules bound, actin quickly becomes denatured . The X-ray crystallography model of actin that was produced by Kabsch from the striated muscle tissue of rabbits is the most commonly used in structural studies as it
2340-471: The "barbed" ends, while the exposed areas of domains II and IV are termed the "pointed" ends. This nomenclature refers to the fact that, due to the small mass of subdomain II actin is polar; the importance of this will be discussed below in the discussion on assembly dynamics. Some authors call the subdomains Ia, Ib, IIa, and IIb, respectively. The most notable supersecondary structure is a five chain beta sheet that
2405-486: The N-terminal. Different recognition sub-units are used for actin or tubulin although there is some overlap. In actin the subunits that bind with prefoldin are probably PFD3 and PFD4, which bind in two places one between residues 60–79 and the other between residues 170–198. The actin is recognized, loaded, and delivered to the cytosolic chaperonin (CCT) in an open conformation by the inner end of prefoldin's "tentacles" (see
2470-711: The Twin Cities 5 liberal arts colleges in Minneapolis-Saint Paul, Minnesota Association for Core Texts and Courses Australian Counter-Terrorism Centre Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title ACTC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=ACTC&oldid=1239240549 " Category : Disambiguation pages Hidden categories: Short description
2535-447: The absence of ATP. In actin's case, two subunits are bound during each conformational change, whereas for tubulin binding takes place with four subunits. Actin has specific binding sequences, which interact with the δ and β-CCT subunits or with δ-CCT and ε-CCT. After AMP-PNP is bound to CCT the substrates move within the chaperonin's cavity. It also seems that in the case of actin, the CAP protein
2600-420: The actin network. Once attached, the rear of the cell body contracts squeezing its contents forward past the adhesion point. Once the adhesion point has moved to the rear of the cell, the cell disassembles it, allowing the rear of the cell to move forward. In addition to the physical force generated by actin polymerization, microfilaments facilitate the movement of various intracellular components by serving as
2665-435: The actin thread, allowing myosin to bind, and muscle contracation to begin. In the final stages of cell division , many cells form a ring of actin at the cell's midpoint. This ring, aptly called the " contractile ring ", uses a similar mechanism as muscle fibers where myosin II pulls along the actin ring, causing it to contract. This contraction cleaves the parent cell into two, completing cytokinesis . The contractile ring
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2730-443: The addition of myosin S1 fragments to tissue that has been fixed with tannic acid . This myosin forms polar bonds with actin monomers, giving rise to a configuration that looks like arrows with feather fletchings along its shaft, where the shaft is the actin and the fletchings are the myosin. Following this logic, the end of the microfilament that does not have any protruding myosin is called
2795-467: The cell nucleus. The level of actin isoforms may change in response to stimulation of cell growth or arrest of proliferation and transcriptional activity. Research on nuclear actin is focused on isoform beta. However the use of antibodies directed against different actin isoforms allows identifying not only the cytoplasmic beta in the cell nucleus, but also alpha- and gamma-actin in certain cell types. The presence of different isoforms of actin may have
2860-652: The cell's structure, trafficking networks, migration, and replication. The multifaceted role of actin relies on a few of the microfilaments' properties: First, the formation of actin filaments is reversible, and their function often involves undergoing rapid polymerization and depolymerization. Second, microfilaments are polarized – i.e. the two ends of a filament are distinct from one another. Third, actin filaments can bind to many other proteins, which together help modify and organize microfilaments for their diverse functions. In most cells actin filaments form larger-scale networks which are essential for many key functions: Actin
2925-481: The different genes that regulate actin production in humans can cause muscular diseases , variations in the size and function of the heart as well as deafness . The make-up of the cytoskeleton is also related to the pathogenicity of intracellular bacteria and viruses , particularly in the processes related to evading the actions of the immune system . Actin's primary role in the cell is to form linear polymers called microfilaments that serve various functions in
2990-426: The energy source for muscle contraction. At times of rest, the proteins tropomyosin and troponin bind to the actin filaments, preventing the attachment of myosin. When an activation signal (i.e. an action potential ) arrives at the muscle fiber, it triggers the release of Ca from the sarcoplasmic reticulum into the cytosol. The resulting spike in cytosolic calcium rapidly releases tropomyosin and troponin from
3055-480: The filament ends can easily release or incorporate monomers. This means that the filaments can be rapidly remodelled and can change cellular structure in response to an environmental stimulus. Which, along with the biochemical mechanism by which it is brought about is known as the "assembly dynamic". Actin can spontaneously acquire a large part of its tertiary structure . However, the way it acquires its fully functional form from its newly synthesized native form
3120-564: The help of molecular motors . Actin therefore contributes to processes such as the intracellular transport of vesicles and organelles as well as muscular contraction and cellular migration . It therefore plays an important role in embryogenesis , the healing of wounds, and the invasivity of cancer cells. The evolutionary origin of actin can be traced to prokaryotic cells , which have equivalent proteins. Actin homologs from prokaryotes and archaea polymerize into different helical or linear filaments consisting of one or multiple strands. However
3185-537: The image and note). The contact when actin is delivered is so brief that a tertiary complex is not formed, immediately freeing the prefoldin. The CCT then causes actin's sequential folding by forming bonds with its subunits rather than simply enclosing it in its cavity. This is why it possesses specific recognition areas in its apical β-domain. The first stage in the folding consists of the recognition of residues 245–249. Next, other determinants establish contact. Both actin and tubulin bind to CCT in open conformations in
3250-458: The in-strand contacts and nucleotide binding sites are preserved in prokaryotes and in archaea. Lastly, actin plays an important role in the control of gene expression . A large number of illnesses and diseases are caused by mutations in alleles of the genes that regulate the production of actin or of its associated proteins. The production of actin is also key to the process of infection by some pathogenic microorganisms . Mutations in
3315-403: The large and the small, which are separated by a cleft centred around the location of the bond with ATP - ADP + P i . Below this there is a deeper notch called a "groove". In the native state , despite their names, both have a comparable depth. The normal convention in topological studies means that a protein is shown with the biggest domain on the left-hand side and the smallest domain on
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#17328513131123380-613: The larger inner domain comprised by sub-domains 3 and 4, and the smaller outer domain by sub-domains 1 and 2. Both the amino and carboxy-termini lie in sub-domain 1 of the outer domain. Actin is a dynamic structure that can adapt two states of flexibility, with the greatest difference between the states occurring as a result of movement within sub-domain 2. Myosin binding increases the flexibility of actin, and cross-linking studies have shown that myosin subfragment-1 binds to actin amino acid residues 48-67 within actin sub-domain 2, which may account for this effect. It has been suggested that
3445-402: The maintenance of the cytoskeleton and, therefore, the organization and movement of organelles, as well as the determination of a cell's shape. However, actin has a wider role in eukaryotic cell physiology, in addition to similar functions in prokaryotes . Monomeric actin, or G-actin, has a globular structure consisting of two lobes separated by a deep cleft. The bottom of the cleft represents
3510-443: The nucleus (for review see: Hofmann 2009. ) The controlled level of actin in the nucleus, its interaction with actin-binding proteins (ABP) and the presence of different isoforms allows actin to play an important role in many important nuclear processes. The actin sequence does not contain a nuclear localization signal. The small size of actin (about 43 kDa) allows it to enter the nucleus by passive diffusion. The import of actin into
3575-535: The nucleus (probably in a complex with cofilin) is facilitated by the import protein importin 9. Low levels of actin in the nucleus seems to be important, because actin has two nuclear export signals (NES) in its sequence. Microinjected actin is quickly removed from the nucleus to the cytoplasm. Actin is exported at least in two ways, through exportin 1 and exportin 6 . Specific modifications, such as SUMOylation, allows for nuclear actin retention. A mutation preventing SUMOylation causes rapid export of beta actin from
3640-616: The nucleus. Nuclear actin exists mainly as a monomer, but can also form dynamic oligomers and short polymers. Nuclear actin organization varies in different cell types. For example, in Xenopus oocytes (with higher nuclear actin level in comparison to somatic cells) actin forms filaments, which stabilize nucleus architecture. These filaments can be observed under the microscope thanks to fluorophore-conjugated phalloidin staining. In somatic cell nuclei, however, actin filaments cannot be observed using this technique. The DNase I inhibition assay,
3705-491: The only test which allows the quantification of the polymerized actin directly in biological samples, has revealed that endogenous nuclear actin indeed occurs mainly in a monomeric form. Precisely controlled level of actin in the cell nucleus, lower than in the cytoplasm, prevents the formation of filaments. The polymerization is also reduced by the limited access to actin monomers, which are bound in complexes with ABPs, mainly cofilin. Different isoforms of actin are present in
3770-401: The point of the arrow (− end) and the other end is called the barbed end (+ end). A S1 fragment is composed of the head and neck domains of myosin II . Under physiological conditions, G-actin (the monomer form) is transformed to F-actin (the polymer form) by ATP, where the role of ATP is essential. The helical F-actin filament found in muscles also contains a tropomyosin molecule, which
3835-447: The right-hand side. In this position the smaller domain is in turn divided into two: subdomain I (lower position, residues 1–32, 70–144, and 338–374) and subdomain II (upper position, residues 33–69). The larger domain is also divided in two: subdomain III (lower, residues 145–180 and 270–337) and subdomain IV (higher, residues 181–269). The exposed areas of subdomains I and III are referred to as
3900-476: The roadway along which a family of motor proteins called myosins travel. Actin plays a particularly prominent role in muscle cells, which consist largely of repeated bundles of actin and myosin II . Each repeated unit – called a sarcomere – consists of two sets of oppositely oriented F-actin strands ("thin filaments"), interlaced with bundles of myosin ("thick filaments"). The two sets of actin strands are oriented with their (+) ends embedded in either end of
3965-546: The same direction. The two ends of the F-actin thread are distinct from one another. At one end – designated the (−) end – the ATP-binding cleft of the terminal actin molecule is facing outward. At the opposite end – designated (+) – the ATP-binding cleft is buried in the filament, contacting the neighboring actin molecule. As F-actin threads grow, new molecules tend to join at the (+) end of an existing F-actin strand. Conversely, threads tend to shrink by shedding actin monomers from
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#17328513131124030-447: The sarcomere in delimiting structures called Z-disks . The myosin fibrils are in the middle between the sets of actin filaments, with strands facing in both directions. When the muscle contracts, the myosin threads move along the actin filaments towards the (+) end, pulling the ends of the sarcomere together and shortening it by around 70% of its length. In order to move along the actin thread, myosin must hydrolyze ATP; thus ATP serves as
4095-489: The scaffolding that allows it to rapidly remodel itself in response to its environment or to the organism's internal signals , for example, to increase cell membrane absorption or increase cell adhesion in order to form cell tissue . Other enzymes or organelles such as cilia can be anchored to this scaffolding in order to control the deformation of the external cell membrane , which allows endocytosis and cytokinesis . It can also produce movement either by itself or with
4160-462: The strand's (−) end. Some proteins, such as cofilin appear to increase the angle of turn, but again this could be interpreted as the establishment of different structural states. These could be important in the polymerization process. There is less agreement regarding measurements of the turn radius and filament thickness: while the first models assigned a length of 25 Å, current X-ray diffraction data, backed up by cryo-electron microscopy suggests
4225-462: Was the first to be purified . The G-actin crystallized by Kabsch is approximately 67 x 40 x 37 Å in size, has a molecular mass of 41,785 Da and an estimated isoelectric point of 4.8. Its net charge at pH = 7 is -7. Elzinga and co-workers first determined the complete peptide sequence for this type of actin in 1973, with later work by the same author adding further detail to the model. It contains 374 amino acid residues. Its N-terminus
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