RESUMO
Three modes of production of the extracellular glucoamylase (GA) in Saccharomyces cerevisiae have been identified; repressed, basal and induced. The repressed mode is found with cells grown in rich media containing non-limiting concentrations of monosaccharides or disaccharides, including GA-hydrolysable maltose, as a sole carbon source. Both the basal and the induced modes (spanned by some seven-fold differences in the rate of GA production) can be displayed by either glucose-limited or glycerol-plus ethanol-consuming cultures; the induced mode is switched over to the basal one due to a feed-back inhibition by extracellularly accumulated GA. It is proposed that the feed-back control involved in GA production can be attenuated by starch which can thus 'induce' higher rates of GA production compared to the basal mode.
