Regulation of glutaminase levels in Escherichia coli

Nitrogenous metabolites, cyclic adenosine 3':5'-monophosphate (cAMP), and the stage of culture growth all influence the levels of glutaminase A in Escherichia coli, but no variables in culture conditions alter the levels of glutaminase B. Growth of E. coli on culture media containing glucose and excess ammonia results in a rise in the level of glutaminase A as the cultures enter stationary phase; this rise is abolished by ammonia limitation. cAMP or glycerol reduce the level of glutaminase A. In mutants deficient in cAMP receptor protein, glutaminase A levels are unchanged by cAMP, but they are still susceptible to regulation by ammonia. We consider glutaminase B to be a constitutive enzyme, since its levels appear independent of nutritional conditions.