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.