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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

F-actin monomer (F-monomer) is formed upon the addition of neutral salt to G-actin. Since F-monomer has a digestibility similar to that of F-actin and much lower than that of G-actin, it has been proposed that F-monomer has a conformation different from that of G-actin and similar to the conformation of the subunits in F-actin. To examine whether F-monomer will enhance the magnesium-activated myosin adenosine triphosphatase (Mg2+-ATPase) as much as F-actin, the ability of partially polymerized actin populations at equilibrium to activate the Mg2+-ATPase of heavy meromyosin was investigated. Correlations were made between ATPase activities and the polymerization state of actin as determined by measurements of viscosity and digestibility. No significant activation of the heavy meromyosin ATPase was observed under conditions where G-actin or mixtures of G-actin and F-monomer were present. As polymer formation occurred at higher actin concentrations, or with increased KCl concentrations, substantial activation characteristic of F-actin was observed. The data suggest that F-monomer may undergo a further conformational change as it forms nuclei or joins onto polymers. Alternatively, the site of actin which activates the myosin ATPase may involve the crevice between two adjacent actin subunits.
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PMID:Activation of heavy meromyosin adenosine triphosphatase by various states of actin. 15 Feb 86

alpha-Actinin isolated from bovine brain migrated on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis like muscle alpha-actinin with an apparent mol.wt. of 100000 and cross-reacted with antibodies to muscle alpha-actinin. Brain alpha-actinin modulated actin-myosin Mg2+-activated adenosine triphosphatase activity and, when bound by polystyrene particles, was found to bind muscle actin and tropomyosin from solution. Brain alpha-actinin, in conjunction with the other components of the contractile and relaxing complex, may play a role in the release of neurotransmitters from synaptic vesicles.
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PMID:Isolation and properties of brain alpha-actinin. 15 45

Histochemical profiles of individual muscle fibres were established using myosin adenosine triphosphatase (myosin ATPase), succinate dehydrogenase (SDHase), and glycogen phosphorylase (GPase) reactions in three muscles (semitendinosus, diaphragm, and pectoralis transversus) of the horse and dog. The major histochemical difference between fibres lies in their myosin ATPase activity; fibres can be subdivided into those with a high and those with a low activity. In horse muscle, all fibres have a high activity of GPase. In the diaphragm and pectoralis transversus, all fibres have a high SDHase activity, but fibres with a low activity of SDHase are also present in samples of the semitendinosus. In dog muscle, all fibres have a high SDHase activity; myosin ATPase low-reacting fibres also have a low activity of GPase. There is a greater fractional area of myosin ATPase high-reacting fibres in the pectoralis transversus and semitendinosus of thoroughbred horses and greyhounds (breeds selected for high speed running) and in the diaphragm of greyhounds. In adults this feature does not appear to be due to training, as are the differences in aerobic and anaerobic capacity (shown in other studies). The preponderance of myosin Atpase high-reacting fibres suggests that there may be differences in the nervous systems of athletes and non-athletes. It is concluded that the proportions of fibre types in muscles are related to the functions of muscles and of their parts. No sex differences or detraining effects were apparent, although the value for the proportion of fibre types (as differentiated by the myosin ATPase reaction) in the limb muscles of thoroughbred crosses lies between those of thoroughbreds and non-thoroughbreds.
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PMID:Differences in the histochemical properties of skeletal muscles of different breeds of horses and dogs. 15 95

1. Muscle fibres may be subdivided into type I (with slow-twitch contractile properties) and type II (fast-twitch) depending on their myosin adenosine triphosphatase activity. In voluntary isometric contractions type I fibres are utilized at low forces (less than 20% of maximum) whereas type II fibres are recruited in addition at high forces. This physiological recruitment order has enabled us to measure the relaxtion rate of type I and II fibres in vivo in normal human subjects. 2. Relaxation rate was measured in 16 subjects from low (10% of maximum) and maximum isometric quadriceps contractions and the muscle-fibre type composition determined from needle-biopsy specimens in 10 subjects. The relaxation rate of type II fibres was calculated to be twice as fast as that of type I. 3. It was not possible to estimate, from studies in 33 quadriceps muscles (25 normal subjects), the contribution of type II fibres to overall fibre area from the relaxation rate as determined from electrically stimulated isometric contractions.
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PMID:Relaxation rate of constituent muscle-fibre types in human quadriceps. 15 28

To investigate the dystrophic influence on the characteristics of actin, a method for the isolation of F-actin filaments from the skeletal muscle of small sizes, i.e., less than 0.5 g, was devised. In this method, minced muscle was treated with collagenase and hyaluronidase, and the isolated filaments were washed with adenosine triphosphate (ATP). Upon examination in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the ATP-washed filaments showed a protein component identical in mobility to actin in untreated myofibrils or to that prepared by the conventional method. Electron microscopic appearances of the filaments were similar to those of F-actin filaments described in the literature. The dimensions of the filaments were 0.5--2.5 micrometer in length and 60--70 A in diameter. The ability to activate the Mg-adenosine triphosphatase or myosin was found to be Ca2+ independent. In all aspects of the above characteristics, the filaments from leg muscles of 129/Re dydy dystrophic mice and their litter mates were observed to be identical.
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PMID:Isolation of F-actin filaments. Comparison of F-actin filament preparations from normal and dystrophic mouse muscle. 15 92

The major contractile protein myosin was isolated and characterized from the smooth muscle of human term placentas. Placental myosin originates chiefly in the anchoring villi which bridge the fetal and maternal surfaces of the placenta. The molecular weight of placental myosin is about 460,000; it is composed of two heavy chains of 200,000 molecular weight and two pairs of light chains with 13,500 and 17,500 molecular weights. The adenosine triphosphatase (ATPase) of the myosin is activated by potassium and calcium and it is inhibited by magnesium. Placental actomyosin ATPase is activated by magensium. Contraction and relaxation of the smooth muscle in the anchoring villi are thought to adjust the volume of the intervillous space; thus, actin-myosin interaction is implicated in the regulation of placental hemodynamics.
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PMID:Isolation and characterization of myosin in the human term placenta. 15 81

From transient kinetic studies of the Mg2+-dependent adenosine triphosphatase of myosin subfragment 1, prepared from rabbit skeletal muscle, a seven-step mechanism has been proposed. Features of this mechanism include two-step processes for ATP and ADP binding in which the binary complex isomerizes in addition to a rapid nucleotide association step. In the case of ATP a large negative standard free energy change is associated with the isomerization. An overall rate-limiting isomerization of the myosin-product complex prior to product release has been identified. Studies on the mechanism of cleavage of ATP bound to the active site indicate the process is readily reversible and can account for the observation that more than one oxygen of the product phosphate arises from water. This proposal has been substantiated by the finding that the oxygen atoms of the gamma-phosphoryl group of bound ATP also undergo extensive exchange with water.
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PMID:Transient kinetic and isotopic tracer studies of the myosin adenosine triphosphatase reaction. 17 37

1. A method is described for the electrophoretic analysis of intact myosin in polyacrylamide gel in a buffer system containing 0.02 M-pyrophosphate and 10% (v/v) glycerol, pH 8.8. 2. In this system chicken skeletal-muscle myosins reveal five distinct electrophoretic components, three components from the fast-twitch posterior latissimus dorsi muscle and two slower-migrating components from the slow-twitch anterior latissimus dorsi muscle. 3. The Ca2+-activated ATPase (adenosine triphosphatase) activity of myosin components was measured by densitometric scanning of the gel for the Ca3(PO4)2 precipitate formed during the ATPase reaction and subsequently for stained protein. Each component from the same muscle appears to have identical ATPase activity, but components from the fast-twitch muscle had an activity 2.2 times higher than those from the slow-twitch muscle. 4. On re-electrophoresis in the same buffer system, individual fractions of fast-twitch myosin did not reproduce the three-band pattern of the original myosin, but migrated at rates consistent with their original mobility. 5. Analysis of the mobility of the three fast-twitch myosin components in gels of different concentrations suggests that they are not stable oligomers of each other. 6. It is suggested that these components of fast-twitch myosin and slow-twitch myosin are isoenzymes of myosin.
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PMID:Electrophoretic analysis of multiple forms of myosin in fast-twitch and slow-twitch muscles of the chick. 18 47

1. A method for the isolation of a new enzyme, myosin light-chain phosphatase, from rabbit white skeletal muscle by using a Sepharose-phosphorylated myosin light-chain affinity column is described. 2. The enzyme migrated as a single component on electrophoresis in sodium dodecyl sulphate/polyacrylamide gel at pH7.0, with apparent mol.wt. 70000. 3. The enzyme was highly specific for the phosphorylated P-light chain of myosin, had pH optima at 6.5 and 8.0 and was not inhibited by NaF. 4. A Ca2+-sensitive 'ATPase' (adenosine triphosphatase) system consisting of myosin light-chain kinase, myosin light-chain phosphatase and the P-light chain is described. 5. Evidence is presented for a phosphoryl exchange between Pi, phosphorylated P-light chain and myosin light-chain phosphatase. 6. Heavy meromyosin prepared by chymotryptic digestion can be phosphorylated by myosin light-chain kinase. 7. The ATPase activities of myosin and heavy meromyosin, in the presence and absence of F-actin, were not significantly changed (+/- 10%) by phosphorylation of the P-light chain.
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PMID:Myosin light-chain phosphatase. 18 30

Fibre-type classification of human skeletal muscle into type I and type II fibres is mostly based on their slight or strong staining with the myosin adenosine triphosphatase reaction. In order to evaluate the reliability of this screening technique a combined histochemical and biochemical study was performed on normal and diseased skeletal muscle of human subjects. In the present investigation activities of enzymes which play a role in the aerobic and anaerobic pathways and which can characterize fibre type, were examined in muscle specimens, with no apparent disease of the neuromuscular system. Special attention is given to the maximal activities of phosphofructokinase and fructose-1,6-diphosphatase, the rate limiting enzymes for the regulation of the glycolysis and glyconeogenesis, respectively. A most important feature of the biochemical findings is the constancy of the activity ratios of the examined enzymes. From these results and from the histochemical results it can be concluded that in apparently normal adult human skeletal muscle the ATP-ase technique for type I and type II typing is reliable. For fibres with an intermediate intensity of staining with the myosin ATPase technique of typing it is also necessary to apply other enzyme histochemical techniques.
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PMID:The value of enzyme histochemical techniques in classifying fibre types of human skeletal muscle. 1. Adult skeletal muscles with no apparent disease of the neuromuscular system. 19 26


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