INFLUENCE OF PHOSPHOLIPASE A(2) FROM NAJA-NAJA-OXIANA VENOM ON THE ACTIVITY OF RAT-BRAIN ISOENZYMES OF NA-ATPASE(,K+)

The specific sensitivity of isoforms of the catalytic subunit of rat b rain Na+,K+-ATPase to phospholipase A(2) (PLA(2)) from Naja naja oxian a venom was studied by analysis of changes in the two-component curve of the dose-dependent inhibition of Na+,K+-ATPase activity by ouabain. Moderate inactivation of Na+,K+-ATPase by PLA(2) was accompanied by a decrease in the apparent affinity to ouabain compared to the intact e nzyme without significant changes in the ratio of isoform activities. This effect, abolished by treatment with serum albumin, is clearly med iated via the formation of fatty acids. With highly inactivated Na+,K-ATPase the alpha-isoform is inactivated more rapidly than the alpha()-isoform.