Palytoxin isolated from marine coelenterates. The inhibitory action on (Na,K)-ATPase

Palytoxin (PTX), C129H223N3O54, a highly toxic substance isolated from zoanthids of Palythoa tuberculosa, inhibited (Na,K)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) prepared from guinea pig heart and hog cerebral cortex in a dose-dependent manner at concentrations greater than 10(-8) M. In the presence of Na (100 mM) and K (20 mM), PTX showed potency nearly equal to that of ouabain. When the ATPase was activated by the various Na concentrations at a constant K concentration, both PTX and ouabain inhibited the ATPase activity noncompetitively. On the other hand, when K concentration was changed at a constant Na concentration, PTX caused a competitive inhibition in all ranges of K concentrations employed, whereas ouabain caused a competitive inhibition at low concentrations and a noncompetitive inhibition at high concentrations.