[Comparative properties of mitochondrial and microsomal NAD(P)H-dependent lipid peroxidation]

Abstract

It was shown that rat liver mitochondria and microsomes contain NADPH- and NADH-dependent systems of enzymatic lipid peroxidation. Activation of the NAD(P)H-dependent process in mitochondria occurs due to inhibition of membrane binding of Fe3+ and Fe2+ by chelators, since the membrane-bound ions of Fe cannot effectively participate in peroxidation. The activity of enzymatic mitochondrial lipid peroxidation decreases at alkaline values of pH. The Michaelis constant for chelated Fe3+ ions under NAD(P)H-dependent mitochondrial peroxidation is by 1,5 order of magnitude more than for microsomal peroxidation. In terms of the chelators' effect on Fe3+ binding by microsomes and peroxidation, as well as pH and Km for Fe3+ the microsomal NADHL-dependent system of lipid peroxidation is similar to mitochondrial NADPH-systems; however, it differs from the latter in the type of dependence of peroxidation on the amount of membranes. Based on the ability of the NADPH-system of microsomes to produce the superoxide radical which participates in initiation of peroxidation together with Fe ions, it is assumed that the decrease of Km for Fe3+ at NAD(P)H-dependent lipid peroxidation in mitochondria and the NADH-process in microsomes can occur in the presence of exogenous sources of active oxygen production.