Lipid oxidation in biological membranes: I. Lipid oxidation in submitochondrial particles and microsomes induced by chaotropic agents

Abstract

Chaotropic agents (SCN −, guanidine-HCl, ClO 4 −, I −, Br −, NO 3 −, urea) destabilize the native structure of Submitochondrial particles and microsomes and render these systems susceptible to lipid oxidation by molecular oxygen. The initial rate of lipid oxidation varies with the concentration and the potency of the chaotropic agent used. The order of decreasing potency of chaotropic agents in inducing lipid oxidation in submitochondrial particles is essentially the same as given above. In electron-transport particles and complexes I, III, and IV of the respiratory chain, lipid oxidation as induced by chaotropic agents shows a rapid initial rate followed by a slower rate. Preparations with a high cytochrome content are capable of lipid oxidation when incubated at 30 ° in the absence of any chaotropic agent. This uninduced reaction is particularly significant in preparations of cytochrome oxidase, which are capable of oxygen consumption at a capacity of 1.76 μmoles O 2/mg of protein. Lipid oxidation in both submitochondrial particles and microsomes results in the production of malondialdehyde. The production of this compound is much greater at the initial phases of lipid oxidation. Substrates impede lipid oxidation in electron-transport particles, and antimycin A inhibits lipid oxidation in complex III. α-Tocopherol, Tiron, and bathophenanthroline sulfonate also inhibit lipid oxidation. Results are discussed in relation to the structure, function, and lipid composition of Submitochondrial particles and microsomes.