The Effect of Cyclic 3’, 5’-Adenosine Monophosphate on the Effect of Glucose, Fructose, and Sucrose Supplements on the Induction of lacZ in Escherichia coli B23 Grown in Minimal Medium with Glycerol

Abstract

Catabolite repression refers to the inhibition of genes whose products are involved in sugar metabolism within cells growing on a preferential carbon source. The transient repression of the lac operon observed when glucose is added to Escherichia coli growing on glycerol is associated with a decrease in the intracellular concentration of cyclic adenosine 3’, 5’-monophosphate (cAMP). Previous studies have shown that sucrose and fructose affect the expression of β -galactosidase activity in induced cells. The basis for these observations was not established. In this study, E.coli B23 was shifted to growth on glucose, sucrose, and fructose in order to determine whether these effects were minimized by exogenous cAMP levels. Cells cultured on glycerol media were induced to express the lac operon for fifteen minutes and then supplemented with an alternative catabolite and cAMP. The results showed similar reduction in measured lac expression in cultures supplemented with glucose, fructose, and sucrose. Exogenous cAMP abolished the glucoseand fructose-mediated repression, but not sucrose. This supports that fructose catabolism is regulated by a mechanism similar to glucose mediated catabolite repression, but sucrose must be acting by some other mechanism.