Adenosine 3′:5′-cyclic monophosphate and catabolite repression in Escherichia coli

摘要

1. Both permanent and transient catabolite repression of β-galactosidase synthesis in Escherichia coli are abolished by 5mm-3′:5′-cyclic-AMP when elicited by glucose, but not when caused by a mixture of glucose, glucose 6-phosphate, gluconate and casein hydrolysate (casamino acids). 2. Glucose uptake is slightly increased by 3′:5′-cyclic-AMP. 3. No significant effects of the nucleotide were found on the synthesis of protein and RNA, either in exponential growth on one substrate, or during a growth shift from glycerol to glycerol plus glucose. 4. Marked changes in the soluble-protein profiles of cells growing in glycerol and glucose were caused by the presence of 3′:5′-cyclic-AMP. 5. Measurements of ¹⁴CO2 release from specifically-labelled glucose showed that 3′:5′-cyclic-AMP greatly stimulated glycolytic activity while having a minor depressing effect on the metabolic flow through the pentose phosphate cycle. 6. The concentrations of several metabolic intermediates, particularly fructose 1,6-diphosphate, were greatly affected by the presence of 3′:5′-cyclic-AMP. 7. Several metabolites partially relieved glucose repression of β-galactosidase synthesis in EDTA-treated cells; three out of five of these metabolites reversed the effect more effectively than did 3′:5′-cyclic-AMP. 8. The evidence for and against a direct role for 3′:5′-cyclic-AMP is discussed. It is concluded that the evidence for indirect action is at least as strong as that for direct action.