Regulation of the adenosine 3', 5'-cyclic monophosphate pool in escherichia Coli

Escherichia coli, adenosine 3',5'-cyclic monophosphate (cAMP) and cAMP receptor protein (CRP) are required for the synthesis of many inducible proteins including/β-galactosidase. Since the concentration of intracellular cAMP affects the synthesis of these proteins, it is important to understand how the cAMP pool in E. coli is regulated. The prerequisite for such studies is a determination of the rates of synthesis, degradation and excretion of cAMP. Previously, a method was not available for a determination of the rates of synthesis and degradation of cAMP in intact JE. coli during exponential growth. A method has been developed for estimating these rates in exponentially growing E. coli cells which depends on a determination of the cAMP pool size and the specific activities of both adenosine 5'-triphosphate and intracellular cAMP. The theory in the method should be applicable to an estimation of the rates of synthesis and degradation of any other cellular component of E. coli during exponential growth. Applying this method, it was found that the cAMP pool sizes in C coli grown on various carbon sources are in approximately direct proportion to the rates of cAMP synthesis and that the combined rates of removal (excretion plus degradation) of cAMP from its pool are directly proportional to the cAMP pool sizes. Using this method it was also shown that the abnormal accumulation of cAMP in an E.. coli CRP- strain (deficient for cAMP receptor protein) is due to the enhanced synthesis rather than decreased degradation of cAMP. A strain was constructed which combined the CRP- character with a deficiency of cAMP phosphodiesterase activity (CPD-). This CRP-CPD- strain accumulated even greater amounts of cAMP than the CRP- strain.