THE EFFECT OF LIPID-PEROXIDATION ON THE ACTIVITY OF VARIOUS MEMBRANE-BOUND ATPASES IN RAT-KIDNEY

Peroxidation of membrane phospholipids is accompanied by alteration of the structural and functional characteristics of membranes. Lipid peroxidation changes the activities of various enzymes. The present study evaluates the effect of lipid peroxidation on the activity of various ATPases localized on kidney membranes. Our experiments were performed on crude preparation of rat kidney membranes which were exposed to Fe(2+.)ADP/NADPH-induced lipid peroxidation. The extent of peroxidation was estimated by measuring the thiobarbituric acid-reactive substances. Simultaneously the activities of different ATPases were determined and divided according to their ouabain sensitivity and Mg(2+)dependency. We found that 10 min incubation of isolated rat kidney membranes at 37 degrees C with inductors of lipid peroxidation increased the production of thiobarbituric acid-reactive substances from 1.10 +/- 0.26 to 7.72 +/- 2.55 nmol malondialde-hyde/mg prot. (+/- SD, n = 4). Under these conditions total ATPase activity was decreased from 681 +/- 77 to 507 +/- 82, ouabain-sensitive Mg2+-dependent ATPase (Na+, K+-ATPase) activity from 249 +/- 54 to 81 +/- 21 and ouabain-insensitive Mg2+-dependent activity from 287 +/- 48 to 173 +/- 58 whereas apparently Mg2+-independent ATPase activity was increased from 145 +/- 37 to 253 +/- 42 nmoles P/min/mg prot. (+/- SD, n = 4), The study indicates different mechanisms by which lipoperoxides affect the function of membrane-bound ATPases activities. It is concluded that the ATPases activities are changed during lipid peroxide formation.