Dual effects of glucose on dicarboxylic acid transport in Kluyveromyces lactis

Abstract

The properties of succinate uptake in succinate-grown Kluyveromyces cells were examined. The rate of succinate transport at 15C exhibits an approximate Vmax of 1.2 μmol × h−1 × mg−1 dry weight of cells and an apparent Km of 18 μM. The uptake process appears to be tightly coupled to metabolism. L-Malate, fumarate, and α-ketoglutarate were the only other dicarboxylates tested, which were found to inhibit succinate transport. The agreement between the order of inhibition of succinate transport by these dicarboxylates and their rates of uptake, as well as the competitive nature of the inhibition are all consistent with the existence of a common carrier system showing specificity for dicarboxylates of the TCA cycle. Cells transferred from succinate to glucose medium rapidly lose their ability to transport succinate. Glucose-grown cells also exhibit an inability to oxidize dicarboxylates or to use them for growth without a very long lag. The dicarboxylate uptake system, therefore, appears to be subject to a strong catabolite repression. The derepression of the succinate transport system requires the presence of succinate, as well as low concentrations of glucose.