K’ transport has been extensively studied in S. cerevisiae . This transport is dependent on plasma membrane potential [12] and exists in two interconvertible forms with different kinetic constants depending on the K’ content of the cells To investigate the stability of this carrier we have followed its activity upon inhibition of protein synthesis by addition of cycloheximide.
Most enzymes in Succlzuromyces cerevisiae are fairly stable in maintaining their catalytic activities for long periods under different metabolic conditions [l-4]. Sugar transport systems behave differently in this respect since a rapid inactivation is observed upon inhibition of protein synthesis [4]. This inactivation, that follows first-order kinetics indicating half-lives in the range of 1-5 h for these carriers [5 -81, is an energydependent process stimulated by fermentable substrates. The characteristics of this inactivation suggest that it is due to proteolysis of these proteins [5-81. To see whether a low stability is a peculiarity of the sugar transports or also affects other carriers of the yeast plasma membrane we have investigated the stability of the K’ transport system.