Identification of two forms of the maltose transport system in Saccharomyces cerevisiae and their regulation by catabolite inactivation

The maltose transport system of Saccharomyces cerevisiae exists in two forms with K_m values of approx. 4 mM and 70 mM, respectively. The V_max of the high-K_m form is about 4-fold greater than the V_max of the low one. A rapid and irreversible inactivation of both forms is detected on protein synthesis impairment. This inactivation is stimulated by the catabolism of fermentable sugars and prevented during ethanol catabolism. It is concluded that both forms of the maltose transport system are regulated by catabolite inactivation.