The nature of the oxidation states of sweet potato mitochondria

Abstract

Sweet potato mitochondria exhibited respiratory control during the oxidation of malate and succinate with ADP/O ratios approaching the theoretical P/O values. Prior to the addition of ADP the mitochondria showed a considerable rate of substrate oxidation, defined as the basic respiration, which was of the same magnitude as state 4 respiration. Electrons from state 4 and the basic respiration were at least partially mediated by the cytochrome chain, as shown by effects of cyanide, azide and amytal, and by spectrophotometric evidence. The nature of ATPase was studied and the influence of inhibitors of ATPase activity on oxidation helped to establish the relationship between the several states of oxidation and ATPase activity. The ADP/O ratio and ADP-stimulated respiration were slightly decreased by fluoride, while state 4, the basic respiration and ATPase activity were effectively inhibited. Chlorpromazine inhibited DNP-stimulated ATPase activity, respiration uncoupled by DNP and all the states of malate oxidation. However, state 4 and basic respiration were less sensitive than was state 3 of malate oxidation to 0.3 mM chlorpromazine. It was concluded that mitochondrial ATPase played a role in the basic respiration and in state 4 oxidation.