Glucose Repression of Inducible Enzyme Synthesis in the Yeast Rhodotorula gracilis

The mechanism of glucose repression of inducible enzyme synthesis in the obligatory aerobic yeast Rhodotorula gracilis has been investigated. Induction of the d ‐xylose catabolizing enzyme system has been used as the test‐tool. It has been found that:1 d ‐Glucose blocks the uptake of d ‐xylose from a mixture of the two aldoses. d ‐Xylose enters the cell interior only after all the d ‐glucose has been consumed. 2 d ‐Fructose, d ‐galactose, d ‐ and l ‐arabinose do not affect the uptake of d ‐xylose. 3 Accordingly, d ‐glucose represses induction of the d ‐xylose catabolizing enzyme system, whereas d ‐fructose, d ‐galactose, d ‐ and l ‐arabinose do not. 4 d ‐Glucose is without effect in cells which have been preincubated with d ‐xylose, whereby the latter is accumulated in the cells. In this case, d ‐xylose catabolism proceeds simultaneously with that of d ‐glucose. 5 d ‐Glucose does not interfere with enzyme induction if d ‐xylose has already been accumulated in the cells. 6 3‐ O ‐Methyl‐ d ‐glucose, an unmetabolizable analogue of d ‐glucose, exhibits the same effect on inducible enzyme synthesis started with d ‐xylose as d ‐glucose does.From these results the following conclusions can be drawn:1 The cell membrane is one of the important regulatory sites of cell metabolism in R. gracilis.2 Glucose repression of inducible enzyme synthesis in R. gracilis is regulated at the cell membrane.