Adenosine triphosphatase calcium-dependent

Levy, J., Zhu, Z., and Dunbar, J. C., 1998, The effect of glucose and calcium on Ca2+-adenosine triphosphatase in pancreatic islets isolated from a normal and a non-insulin-dependent diabetes mellitus rat model. Metabolism, 47 185-9. 

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." ... 

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. 

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