The glucose analog, 3-0-methyl-~-glucose, inhibited growth of yeast on non-fermentable carbon sources. The sugar was phosphorylated by the yeast and also in vitro by a commercial preparation of yeast hexokinase. The chromatographic behaviour of the phosphorylated product was identical in both cases. This suggests that 3-0-methyl-D-glucose is phosphorylated to form 3-0-methyl-~-glucose 6-phosphate. The inhibition of the growth appears to be due to interference with the derepression of several enzymes necessary to grow on non-fermentable carbon sources. Spontaneous mutants whose growth was unaffected by 3-O-methyl-~-glucose were isolated. In these mutants there was no significant accumulation of the phosphorylated ester and the derepression of the enzymes tested was not affected by the glucose analog.Glucose causes inactivation and repression of several enzymes in yeast. These phenomena are known as catabolite inactivation [l] and catabolite repression [2]. The mechanisms underlying them are not well known although, in some particular cases, biochemical and genetic approaches have allowed the elaboration of a plausible hypothesis [3, 41. The use of some non-metabolizable glucose analogs like D-glucosamine and 2-deoxyglucose which are phosphorylated by yeast hexokinase has produced useful mutants for the study of catabolite repression [5, 61. It appeared of interest to evaluate the effects upon catabolite repression of a glucose analog not phosphorylated by hexokinase. We chose for this purpose 3-0-methyl-~-glucose (3 MeGlc) which has been shown to be a substrate for the glucose transport system in different organisms [7 -91 and appeared to be metabolically inert [ 101.This article shows that, contrary to current belief, 3 MeGlc is phosphorylated by yeast cells. This phosphorylation appears to be a prerequisite for the ability of the analog to interfere with the derepression of some enzymes subject to catabolite repression.
MATERIALS AND METHODS
Yeast strain andgrowth conditionsSaccharomyces cerevisiae F-11 a his1 ade can1 provided by Dr J. Conde (Sevilla, Spain) was used. The organisms were grown on liquid media with 1% yeast extract, 1% peptone and the adequate carbon source at a final concentration of 2%. Growth was followed turbidimetrically at 660 nm.