Cyclic adenosine 3',5'-monophosphate regulation of membrane energetics in Escherichia coli

Mutants of Escherichia coli K-12 lacking functional adenylate cyclase (cya) or the cyclic adenosine 3',5'-monophosphate (cAMP) receptor protein (crp) were compared with their wild type to evaluate the role played by the cAMP-cAMP receptor protein complex in regulating this organism's membrane-associated bioenergetic functions. Both mutants were found to be equally defective in carrying out various electron transport activities. In particular, their capacity for synthesizing a functional oxygen-linked transhydrogenase system was totally repressed, and their content of flavin adenine dinucleotide was reduced by approximately 85%. In addition, it was found that the mutant strains had a decreased ability to generate a protonmotive force and to use this chemiosmotic force to generate adenosine 5'-triphosphate. All these membrane-associated dysfunctions were completely restored to the wild-type state when the cya cells were grown in the presence of exogenous cAMP. As would be expected if these controls were operating at the transcriptional level, the crp cells retained the mutant character even when grown in the presence of this cyclic nucleotide.