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

Abstract

A dramatic increase in the rate of oxidation of an organic acid by bacterial cells often occurs when the concentration of hydrogen ions or of the substrate is grossly increased. As an explanation, t,he effect may be due to a permeability response at the cell surface or, alt,ernatively, to an enzymatic change internally. The present experiment#s were designed to distinguish between these possibilities in the oxidation of succinate by Brucella abortus, in which the rate of the reaction is markedly altered with adjustment of pH and substrate concentration, and to analyze the effect in terms of substrate ionization. For want of direct methods of measuring the penetration process in whole cells, a comparison of t,he relat,ive changes in the rates of oxygen and substrate uptake with adjustment of pH and concent,rat,ion first was made. The effect of pH and concentration changes on oxidat,ion, uptake, and intermediate accumulat,ion with succinate as compared to a reported metabolic precursor, glutamate, gave substantiating informat,ion. Further investigation of the two variables revealed a11 interdcpendency and a possible basis of their action. Finally, t'he changes that accompanied physical disruption of the cells were studied. The results generally favored the explanation that the test variables exert an external influence on the dissociation of succinate, upon which utilization by the cell is primarily but not exclusively dependent.