The NADH-Oxidase Activity of Mitochondria under Hypotony with Respiratory Chain Inhibitors

Abstract

We studied the contribution of NADH oxidase to mitochondrial respiration in a suspension under extreme conditions: in a hypotonic medium and with respiratory poisons rotenone, antimycin, and sodium azide. The experiment was carried out with rat liver mitochondria. It was shown that not only cytochrome oxidase but also NADH dehydrogenase of the respiratory chain notably consume oxygen to oxidize exogenous NADH. For this reason NADH-associated mitochondrial respiration is not completely inhibited by respiratory poisons. The insensitivity of respiration to poisoning is a result of a shunt of electron transfer from NADH to oxygen directly via NADH dehydrogenase. This residual respiration via NADH oxidase, which is insensitive to respiratory chain inhibitors, may account for one-half of the total oxygen consumption under extreme conditions.