Effects of palytoxin on cation occlusion and phosphorylation of the (Na+,K+)-ATPase.

Autor:	Tosteson, M T, Thomas, J, Arnadottir, J, Tosteson, D C
Předmět:	ACRYLAMIDE ADENOSINE triphosphatase BIOCHEMISTRY CATIONS CELLULAR signal transduction COMPARATIVE studies DOSE-effect relationship in pharmacology PHENOMENOLOGY RESEARCH methodology MEDICAL cooperation METALS PHOSPHATASES PHOSPHORUS PHOSPHORYLATION POTASSIUM RESEARCH SODIUM EVALUATION research
Zdroj:	Journal of Membrane Biology; Apr2003, Vol. 192 Issue 3, p181-189, 9p
Abstrakt:	Palytoxin (PTX) inhibits the (Na(+) + K+)-driven pump and simultaneously opens channels that are equally permeable to Na+ and K+ in red cells and other cell membranes. In an effort to understand the mechanism by which PTX induces these fluxes, we have studied the effects of PTX on: 1) K+ and Na+ occlusion by the pump protein; 2) phosphorylation and dephosphorylation of the enzyme when a phosphoenzyme is formed from ATP and from P(i); and 3) p-nitro phenyl phosphatase (p-NPPase) activity associated with the (Na+, K+)-ATPase. We have found that palytoxin 1) increases the rate of deocclusion of K+(Rb+) in a time- and concentration-dependent manner, whereas Na+ occluded in the presence of oligomycin is unaffected by the toxin; 2) makes phosphorylation from P(i) insensitive to K+, and 3) stimulates the p-NPPase activity. The results are consistent with the notion that PTX produces a conformation of the Na+, K(+)-pump that resembles the one observed when ATP is bound to its low-affinity binding site. Further, they suggest that the channels that are formed by PTX might arise as a consequence of a perturbation in the ATPase structure, leading to the loss of control of the outside "gate" of the enzyme and hence to an uncoupling of the ion transport from the catalytic function of the ATPase. [ABSTRACT FROM AUTHOR]
Databáze:	Complementary Index
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