The effect of ammonia on the oxidation of glucose by Zygorhyncus moelleri

Abstract

Zygorhyncus moelleri was grown in a glucose-ammonium chloride medium and then starved for 24 hours in a carbohydrate-free medium. When glucose was added to the starved cells an induction period of 2-3 hours was observed before the rate of O2 uptake rose to a constant maximum value. In the presence of azide the final rate of O2 uptake was somewhat lower than in its absence, although the length of the induction period was not greatly affected. These cells were not N-starved. The respiration of suspensions starved of both carbohydrate and N was not inhibited by azide, but was greatly stimulated by small quantities of NH4Cl. This stimulation was abolished by suitable concentrations of azide and cyanide. Neither the endogenous respiration nor the fermentation of glucose under anaerobic conditions was affected by added NH4Cl. L-Glutamic acid, L-aspartic aicd, L-asparagine, and urea stimulated glucose oxidation, though none so effectively as ammonia; nitrate, nitrite, and hydroxylamine were inactive. The oxidation rates of sucrose, ethanol, acetate and succinate were also stimulated to varying degrees by ammonia, but the stimulation was much weaker in most cases than with glucose; only with sucrose did the stimulation approach that with glucose. In the presence of glucose the ammonia was bound, and after 3 hours appeared mainly in the insoluble N fraction; azide inhibited this binding of ammonia. These results are discussed and it is suggested that enzyme adaptation is a possible interpretation of these phenomena consistent with the observed facts.