Phosphohydrolase, ATP

Cande and Wolniak (54) found that vanadate did not potently inhibit glycerlnated myofibril contraction or myosin ATPase activity. Those findings suggest that vanadate would be an ideal specific inhibitor of (Na, K)-ATPase or dyneln ATPase. 

Magnesium and potassium facilitate vanadate Inhibition of (Na, K)-ATPase activity and they both appear to bind synerglstically with vanadate (56). ATP depressed vanadate inhibition of enzyme activity (48). On the other hand. Gibbons 

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

Cantley al. (50) found that vanadate binds to one high-affinity and one low affinity site per (Na, K)-ATPase enzyme molecule. The low-affinity site was apparently responsible for inhibition of (Na, K)-ATPase activity and was the high-affinity ATP site where sodium-dependent protein phosphorylation occurs. Cantley al. (56) proposed that the unusually high affinity of vanadate for (Na, K)-ATPase was due to its ability to form a trigonal blpyramldal structure analogous to the transition state for phosphate hydrolysis. 

Cantley al. (50) found that vanadate was transported to the red blood cell where it inhibited the sodium pump by binding to (Na, K)-ATPase from the cytoplasmic side (the site of ATP hydrolysis). They suggested that the vanadium in mammalian tissue acts as a regulatory mechanism for the sodium pump that maintains a high intracellular id to Na ratio by coupling with ATP hydrolysis. 

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See also in sourсe #XX -- [ ]

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