Inactivation of the galactose transport system in Saccharomyces cerevisiae

The galactose transport system of Saccharomyces cerevisiae consists of one component which shows a Km value of approx. 4mM in growing cells. A rapid and irreversible inactivation of this transport is detected on impairment of protein synthesis. This inactivation shows the following characteristics: (i) it is due to changes in the Km and Vmax of the transport system; (ii) it follows first-order kinetics; (iii) it is an energy-dependent process and is stimulated by the presence of an exogenous carbon source; (iv) fermentable sub-dependent process and is stimulated by the presence of an exogenous carbon source; (iv) fermentable substrates stimulate inactivation more efficiently than non-fermentable substrates.