Mode of lipid peroxidation-induced inhibition of Na, K-ATPase

Experimental data are presented concerning inhibition of Na, K-ATPase in rat heart sarcolemmal and rat brain synaptosomal membranes upon generation of activated oxygen species. It is shown that the activity of Na, K-ATPase is inhibited in membranes of both types during incubation with Fe2+ + ascorbate system, which generates O2 and OH- radicals and thus induces lipid peroxidation. The inhibitory effect is linearly dependent on the amount of the lipid peroxidation products (malondialdehyde) accumulated. Exogenous unsaturated phosphatidylethanolamine, when added to partially inactivated enzyme, does not produce reactivation of Na, K-ATPase. Free radical scavenger 4-methyl-2,6-di-(tertbutyl) phenol exerts both inhibition of lipid peroxidation and protection of Na, K-ATPase. Mg-ATPase is resistant to the action of lipid peroxidation inducing system. Bubbling of oxygen through membrane suspension results in no malondialdehyde accumulation, but is accompanied by Na, K-ATPase inhibition, which could not be prevented by free radical scavengers. It is suggested that generation of activated oxygen species results in oxidation of one of the essential amino acid residues in the active site of the enzyme.