Regulation of adenylate cyclase in E. coli.

The intracellular concentrations of cAMP in Escherichia coli are regulated mainly by control of the activity of adenylate cyclase. Withdrawal of the carbon source from the growth medium causes a gradual reduction of cellular energy and a dramatic stimulation of cyclase activity. Manipulations of the proton gradient at the cell membrane of ATP synthase-deficient E. coli (unc-) revealed that this part of the energy compartment is not responsible for the starvation-induced stimulation of cyclase. Neither is the ATP pool involved in regulation of the activity of the cyclase. The intracellular concentrations of ATP were experimentally lowered by purine starvation of auxotrophs, by inhibition of purine synthesis using amethopterin, or by affecting ATP synthesis using arsenate. None of these conditions led to stimulation of cyclase activity. The control of cyclase is exerted not via the energy pools but via uptake systems of energy substrates independent of whether the substrate can be metabolized or not, or how the transport is energized. The stringent coupling between these transport systems and cyclase activity enables the cell to react instantaneously to changes in its environment.