Novel aspect of cyclic 3',5'-adenosine monophosphate synthesis in Escherichia coli 3000A1

A kinetic analysis of cyclic 3',5'-adenosine monophosphate (cAMP) synthesis in an adenine auxotroph of Escherichia coli 3000 was made by assaying the incorporation of [3H]adenine into cAMP during exponential growth. The rate of increase in intracellular [3H]cAMP was very slow (0.1-0.2 pmol/min/DU660). The steady state level was attained at about 40-min incubation after the addition of [3H]adenine, and was estimated to be 5 to 7 pmol/DU660. The rate and level of intracellular cAMP were scarcely affected by growth conditions, such as change of carbon source, whereas the excretion of cAMP into the medium began immediately after the addition of [3H]adenine, and continued at a rate of 5 to 7 pmol/min/DU660 in the glycerol medium. The excretion rate decreased to 1.4 pmol/min/DU660 in the presence of glucose. These results are inconsistent with the view that the excretion rate is dependent on the intracellular concentration of cAMP. Although the decreased rate of cAMP synthesis in the presence of glucose accounts for the permanent catabolite repression of inducible enzyme systems, no immediate depression in cAMP synthesis, which might account for the transient repression, was found after the addition of glucose.