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 per oxidation 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 a nd 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 produc tion of thiobarbituric acid-reactive substances from 1.10 +/- 0.26 to 7.72 +/- 2.55 nmol malondialde-hyde/mg prot. (+/- SD, n = 4). Under th ese conditions total ATPase activity was decreased from 681 +/- 77 to 507 +/- 82, ouabain-sensitive Mg2+-dependent ATPase (Na+, K+-ATPase) a ctivity from 249 +/- 54 to 81 +/- 21 and ouabain-insensitive Mg2+-depe ndent activity from 287 +/- 48 to 173 +/- 58 whereas apparently Mg2+-i ndependent 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-boun d ATPases activities. It is concluded that the ATPases activities are changed during lipid peroxide formation.