Phosphate and salt uptake by bakers' yeast.

Abstract

UPTAKE of phosphate by Saccharomyces cervisiae has three components as indicated by first-order kinetic analysis of uptake under steady-state conditions as a function of phosphate concentration. Two of these components, having Michaelis–Menten constants K m = 10−5 and 10−3, respectively, are evident on a plot of rate of uptake m against m/phosphate concentration1 (Fig. 1). Action of glycolytic and respiration inhibitors, including anaerobiosis—illustrated by the action of iodoacetate (Fig. 1)—indicates that both these components are coupled to oxidative phosphorylation associated with the action of glyceraldehyde-3-phosphate dehydrogenase. The component reaction with K m = 10−5 is found to be rate-limited by formation of adenosine triphosphate, which acts as a competitive inhibitor in the oxidative phosphorylation, and the component with K m = 10−3 by the action of hexokinase, which becomes rate-limiting for utilization of adenosine triphosphate. The coupling of phosphate uptake with glycolysis, but not its components, was recognized by Strickland2 and Goodman and Rothstein3. Rothstein4, in particular, has related the uptake to glycolytic activity at a membrane surface.