Regulation of sugar transport systems of Kluyveromyces marxianus: the role of carbohydrates and their catabolism.

In Kluyveromyces marxianus grown on a glucose-containing synthetic medium four different sugar transporters have been identified. In cells, harvested during the exponential phase, only the constitutive glucose/fructose carrier, probed with 6-deoxy-D-glucose or sorbose, appeared to be active. In cells from the stationary phase three proton symporters can be active, recognizing 6-deoxyglucose (a glucose/galactose carrier), sorbose (a fructose carrier) and galactosides (lactose carrier), respectively. These symporters appeared to be sensitive to catabolite inactivation. This process is induced by incubating cells in the presence of glucose, fructose or mannose. Catabolite inactivation was not influenced by the inhibitor of protein synthesis, anisomycin. Derepression of the proton/sorbose and the proton/galactoside symporters proceeded readily when cells were incubated in a medium without glucose. Activation of the proton/galactose symporter needed, in addition, the presence of specific molecules (inducers) in the medium. The activation of each of these active transport systems was inhibited by anisomycin, showing the involvement of protein synthesis.