Studies on Dihydronicotinamide Adenine Dinucleotide Ubiquinone Reductase

Abstract

Mitochondrial particles prepared by exposing mitochondria to sonic oscillation catalyzed the oxidation of reduced nicotinamide adenine dinucleotide by ubiquinone-6, ubiquinone-10, the lower homologues of ubiquinone, and menadione.Ubiquinone-6 reduction activity was inhibited completely by rotenone and by amytal.Menadione reduction was also inhibited, but only partially, suggesting multiple sites of interaction of menadione with the respiratory chain.The extraction of a soluble reduced nicotinamide adenine dinucleotide ubiquinone reductase from mitochondrial particles is described.The assay conditions for measuring the reduced nicotinamide adenine dinucleotide ubiquinone reductase activity of particulate and soluble preparations are described in detail.The assay, which is carried out in a heterogeneous system containing ubiquinone in suspension, is sensitive to a variety of factors.