Two types of glucose effects on beta-galactosidase synthesis in a membrane fraction of Escherichia coli: correlation with repression observed in intact cells

Abstract

A membrane fraction obtained from an osmotic lysate of Escherichia coli spheroplasts retains capability to synthesize beta-galactosidase. The system also retains cellular regulatory functions, one of which is known as catabolite repression. Two types of repression of beta-galactosidase synthesis were observed in this membrane system: one was caused by the addition of 2-deoxyglucose or glucose at a low concentration (3 times 10- minus 4 M), and the other was caused by glucose-6-phosphate or glucose at a high concentration (3 times 10- minus 2 M). In the presence of cyclic adenosine 3',5'-monophosphate (10 mM), repression caused by the former was completely reversed, whereas repression by the latter was only partially reversed. Conditions in intact cells causing transient and permanent repression were also investigated. Upon addition of 2-deoxyglucose or glucose at a low concentration to intact cells, only transient repression of beta-galactosidase synthesis was observed. Glucose at a high concentration caused both transient and subsequent permanent repression, and intensity of permanent repression depended upon glucose concentration, whereas duration and intensity of transient repression were independent of glucose concentration. Mutants deficient in phosphoenolpyruvate-phosphotransferase system (Hpr minus and enzyme I minus) showed transient repression but failed to show permanent repression. In mutants deficient in glucose catabolism beyond glucose-6-phosphate, both transient and permanent repression were observed. Correlation between the observations in the membrane system and in intact cells is discussed. The results obtained here strongly suggest that transient repression is caused by glucose itself, and that permanent repression is caused by glucose-6-phosphate of high intracellular levels of glucose.