NADH- and NADPH-dependent lipid peroxidation in bovine heart submitochondrial particles. Dependence on the rate of electron flow in the respiratory chain and an antioxidant role of ubiquinol

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Abstract
Malondialdehyde formation by bovine heart submitochondrial particles supported by NADH or NADPH in the presence of ADP and FeCl3 was studied. The NADH-dependent reaction was maximal at very low rate of electron input from NADH to the respiratory chain and it decreased when the rate became high. The reaction was stimulated by rotenone and inhibited by antimycin A when the input was fast, whereas it was not affected by the inhibitors when the input was slow. The input rate of the electrons from NADPH was also so low that the reaction supported by NADPH was not affected by the inhibitors. Most of the endogenous ubiquinone in the particles treated with antimycin A was reduced by NADH even in the presence of ADP-Fe3+ chelate, but ubiquinone was not reduced by NADPH when AOP-Fe3- was present. Succinate strongly inhibited both NADPH- and NADPH-dependent lipid peroxidation. The inhibition was abolished when ubiquinone was removed from the particles, and it appeared again when ubiquinone was reincorporated into the particles. Reduced ubiquinone-2 also inhibited the peroxidation, but duroquinol, which reduces cytochrome b without reducing endogenous ubiquinone, did not. Thus the malondialdehyde formation appeared to be inversely related to the extent of the reduction of endogenous ubiquinone. Both NADH- and NADPH-dependent lipid-peroxidation reactions may be closely related to the respiratory chain and the peroxidation may be controlled by the concentration of reduced ubiquinone.

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