Dinitrocresol, Cyanide, and the Pasteur Effect in Yeast

Abstract

At pH 5-o the respiration of yeast is stimulated by low concentrations of 3:5-dinitro-o-cresol, reaching a peak level of 170 per cent, at io~5 M. Con centrations above this inhibit oxygen uptake and cause aerobic fermentation to appear, which in turn reaches a peak value and is then inhibited. The rate of carbohydrate breakdown, or glycolysis, calculated from the rates of respiration and aerobic fermentation, increases steadily up to 3 X io~5 M., at which concentra tion it is S times faster than the control : higher concentrations depress the rate of glycolysis. The rate of fermentation under nitrogen is about twice that of respiration, and it is inhibited over the same concentration range as aerobic fermentation. It was found earlier that oxidative assimilation of glucose by yeast is pro gressively inhibited by increasing concentrations of dinitrocresol, and it is now shown that this parallels the increase in the rate of aerobic glycolysis. It is argued that dinitrocresol is here acting as an uncoupling agent and that both oxidative assimilation and the rate of glycolysis are controlled by the level of energy-rich phosphate. With cyanide there is no stimulation of oxygen uptake, aerobic fermentation only appears when respiration becomes inhibited, and after an initial slight decrease the rate of glycolysis rises to 575 per cent, of the control value at 5 X io~4 M. It is suggested that the rate of glycolysis only increases when respiration has been inhibited sufficiently to reduce the rate of formation of energy-rich phosphate.