Relationship Between Sugar Structure and Competition for the Sugar Transport System in Bakers' Yeast

Abstract

Twenty-five sugars have been compared as inhibitors of l -sorbose or d -xylose transport by the constitutive, monosaccharide transport system in bakers' yeast. d -Glucose showed the highest activity (i.e., apparent K i = 5 m m ). Since all sugars except 2-deoxyglucose showed a decrease in activity relative to glucose (i.e., apparent K i = 25 − >2,000 m m ), an attempt was made to relate the activity of each sugar with the way its structure differs from that of d -glucose. Assuming that the inhibition was the result of sugar-carrier complex formation, the analysis showed that the transport system has a rather broad specificity for pyranoses. Single changes at each of the five carbons of d -glucose (except for the 2-deoxy derivative) result in variable decreases in activity depending upon the carbon number and the alteration. The largest decrease in activity effected by a single change is the methylation or glucosylation of the anomeric hydroxyl. The combination of two or more changes leads to a decrease which is greater than the decrease in activity resulting from the individual changes occurring alone.