Myosin triphosphatase

There have been no reports thus far of experiments demonstrating whether or not the reversible diminution in catalytic activity of purified enzyme preparations, such as trypsin (8), is counteracted by increased hydrostatic pressure but the pressure activation, under certain conditions, of myosin triphosphatase has been reported (32). 

Contraction of muscle follows an increase of Ca " in the muscle cell as a result of nerve stimulation. This initiates processes which cause the proteins myosin and actin to be drawn together making the cell shorter and thicker. The return of the Ca " to its storage site, the sarcoplasmic reticulum, by an active pump mechanism allows the contracted muscle to relax (27). Calcium ion, also a factor in the release of acetylcholine on stimulation of nerve cells, influences the permeabiUty of cell membranes activates enzymes, such as adenosine triphosphatase (ATPase), Hpase, and some proteolytic enzymes and facihtates intestinal absorption of vitamin B 2 [68-19-9] (28). 

Hiratsuka, T. (1987) Nucleotide-induced change in the interaction between the 20- and 26-kilodalton heavy-chain segments of myosin adenosine triphosphatase revealed by chemical cross-linking via the reactive thiol SH2. Biochemistry 26, 3168. 

Hiratsuka, T. (1988) Cross-linking of three heavy-chain domains of myosin adenosine triphosphatase with a trifunctional alkylating agent. Biochemistry 27, 4110. 

Voluntary muscles contain a variety of fibre types which are specialized for particular tasks. Most muscles contain a mixture of fibre types although one type may predominate. All human skeletal muscles are composed of several different muscle fibre types. Up to seven different fibre types have been identified histochemically based on the pH stability of myofibrillar adenosine triphosphatase and on the myosin heavy chain profile. Innumerable fibre type transients exist due to continuing adaptation processes. However, three main... 

Bagshaw, C. R., and Trentham, D. R. (1974). The characterization of myosin-product complexes and of product-release steps during the magnesium ion-dependent adenosine triphosphatase reaction. Biochem.J. 141, 331-349. 

Brooke, M. H. and Kaiser, K. K. (1970) Three myosin adenosine triphosphatase systems the nature of their pH lability and sulfhydryl dependence, J. Hlstochem. Cytochem. 18 670-2. 

Sreter, F. A., Seidel, J. C., and Gergely, J., Studies on myosin from red and white skeletal muscles of the rabbit. I. Adenosine triphosphatase activity. J. Biol. Chem. 241, 5772-5776 (1966). 

Caldesmon is a cytoplasmic protein with two isoform classes, one of which is found predominantly in smooth muscle cells and other cell types with partial myogenic differentiation. High-molecular-weight isoforms with molecular weights between 89 and 93 kD are capable of binding to actin, tropomyosin, calmodulin, myosin, and phospholipids, and they function to counteract actin-tropomyosin-activated myosin adenosine triphosphatase (ATPase). As such, they are mediators for the inhibition of calcium-dependent smooth muscle contraction." ... 

The magnitudes of entropies of activation have provided valuable information regarding the details of the interactions between enzymes and substrates. The process of muscular contraction involves an interaction between the muscle enzyme myosin and adenosine triphosphate (ATP). Myosin is an enzyme which catalyzes the hydrolysis of ATP, a process which we have seen (p. 246) to be more exergonic than is the case for many other phosphates, and this hydrolysis contributes energy for contraction. Because of its catalytic action, myosin is also referred to as adenosine triphosphatase (ATP-ase). When the activated complex is formed from ATP ase and its substrate ATP, the entropy of activation is about 41 cal K" mol under approximately normal physiological conditions. We saw on p. 400, on the basis of a very simple electrostatic theory of AS values for ionic reactions in aqueous solution, that there will be a positive contribution of about 10 cal mol for each unit of the product [ [ % ( The long myosin molecules bear a series of positive... 

Onishi H, Suzuki H, Nakamura K, Takahashi K, Watanabe S (1978) Adenosine triphosphatase activity and thick filament formation of chicken gizzard myosin in low salt media. J Biochem (Tokyo) 83 835-847... 

This enzyme activity has been observed in myosin and actomyosin, mitochondria, microsomes, and cell membranes. In some cases magnesium ions function as an activator, in others calcium ions, and in still others, both calcium and magnesium are requited. Another form of adenosine-triphosphatase is stimulated by sodium and potassium ions and is inhibited by ouabain. Some forms of the enzyme can hydrolyse inosine triphosphate and other nucleoside-5 -triphosphates. The substrate specificity may depend upon the activating divalent cation and on the presence of monovalent cations. These enzymes are probably important components of a system responsible for facilitating cation transfer in membranes. They should not be confused with adenosine triphosphate pyrophosphatase E.C. 3.6.1.8. 

Finally, it should be pointed out that a number of other phosphohydrolases such as myosin ATPase, nucleoside triphosphatases, and acid or alkaline phosphatases have been shown to catalyse the hydrolysis of ThTP with variable but low degree of efficiency. Two different enzymes hydrolysing ThTP have been reported in E. coli, but they have not been characterized. 

Myosin is an NTPase hydrolase enzyme. Nucleoside triphosphatases (NTPases) are one of the most important enzymes in living cells. A very large number of NTPase enzymes associated with a wide range of biological functions are known. 

Calcium stimulates myosin-adenosine triphosphatase (ATPase) activity. 

Preparation of an immobilized form of myosin and characterization of the adenosine triphosphatase activity generated... 

Flock and Bollman (62,53), using myosin adenosine triphosphatase (ATPase) as a tool for differentiating between the two labile groups of ATP, have found, in experiments lasting one hour, a higher P concentration in the terminal phosphate group than in the second phosphate group (Table II). After the lapse of one day, the specific activity of the two... 

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