The metabolism of Brucellae: The nature of the effects of pH and concentration on the rate of oxidation of succinate

Abstract

The sharp rise in the rate of oxidation of succinate by Brucella abortus that occurs with gross increases in hydrogen ion or the substrate concentration was accompanied by an even greater degree of increase in the rate of substrate uptake. The degree of change in these rates and of pyruvate formation with glutamate, a reported precursor of succinate, was minimal in comparison to that with succinate. The optimal pH for oxidation of succinate became strikingly higher with increased concentration of substrate; similarly, concentration optima were observed and they rose with increased pH. An analysis of these data indicated that the activity was largely but not exclusively dependent on the concentration of undissociated molecules. Contrary to these findings with intact cells, crude succinoxidase preparations exhibited a constant pH optimum at neutrality with changes in substrate concentration. The results favored a conclusion that permeability is rate limiting in the oxidation of succinate by the organism.