Escherichia coli adenylate cyclase complex: regulation by the proton electrochemical gradient.

Abstract

Sugars such as glucose are transported into E. coli by a coupled phosphorylation mechanism (the phosphoenolpyruvate:sugar phosphotransferase system, PTS). Transport of sugars through the PTS results in inhibition of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity by a mechanism involving a change in the state of phosphorylation of PTS proteins. Other sugars (e.g., lactose) are transported without modification by a mechanism involving proton co-transport, which requires a proton motive force across the cell membrane. Uptake of sugars through the lactose transport system results in inhibition of adenylate cyclase activity if the proton symport mechanism is also active. The protonophore carbonyl cyanide m-chlorophenylhydrazone also inhibits adenylate cyclase activity. Apparently the steady-state electrochemical proton gradient regulates the activity of adenylate cyclase. Sugar-dependent inhibition of adenylate cyclase activity may occur by either of 2 mechanisms. Sugars transported by the PTS inhibit adenylate cyclase activity by dephosphorylation of a regulatory protein, while sugars transported by the proton motive force system inhibit adenylate cyclase activity as a result of collapse of the proton electrochemical gradient.