Differential sensitivities of the two malate dehydrogenases and the maltose permease to the effect of glucose in Saccharomyces carlsbergensis.

In Saccharomyces carlsbergensis the two malate dehydrogenase activities, which are localized in different compartments of the cell, were found to differ in their response to glucose. The cytoplasmic malate dehydrogenase activity appears to be sensitive to inactivation by very low concentrations of glucose. The mitochondrial malate dehydrogenase activity is only repressed at a higher glucose concentration. Maltose permease is also sensitive to inactivation by glucose. Conditions were found such that the maltose permease was present while the cytoplasmic malate dehydrogenase was inactivated. The different sensitivities of the two malate dehydrogenases and maltose permease to the effect of glucose may explain the preferential use of glucose, maltose, and products of glucose metabolism (2- and 3-carbon skeletons) as carbon sources for growth in the order as mentioned.