Kinetics of active ?-glucoside transport in

Abstract

α-Glucosides are the most abundant fermentable sugars in the industrial applications of Saccharomyces cerevisiae, and the active transport across the plasma membrane is the rate-limiting step for their metabolism. In this report we performed a detailed kinetic analysis of the active α-glucoside transport system(s) present in a wild-type strain, and in strains with defined α-glucoside permeases. Our results indicate that the wild-type strain harbors active transporters with high and low affinity for maltose and trehalose, and low-affinity transport systems for maltotriose and α-methylglucoside. The maltose permease encoded by the MAL21 gene showed a high affinity (Km∼5 mM) for maltose, and a low affinity (Km∼90 mM) for trehalose. On the other hand, the α-glucoside permease encoded by the AGT1 gene had a high affinity (Km∼7 mM) for trehalose, a low affinity (Km∼18 mM) for maltose and maltotriose, and a very low affinity (Km∼35 mM) for α-methylglucoside.