Excess capacity of H⁺ ATPase and inverse respiratory control in Escherichia coli

With succinate as free-energy source, Escherichia coli generating virtually all ATP by oxidative phosphorylation might be expected heavily to tax its ATP generating capacity. To examine this the H+-ATPase (ATP synthase) was modulated over a 30-fold range. Decreasing the amount of H+-ATPase reduced the growth rate much less than proportionally; the H+-ATPase controlled growth rate by lt 10%.

This lack of control reflected excess capacity: the rate of ATP synthesis per H+-ATPase (the turnover number) increased by 60% when the number of enzymes was decreased by 40%. At 15% H+-ATPase, the enzyme became limiting and its turnover was increased even further, due to an increased driving force caused by a reduction in the total flux through the enzymes.

At smaller reductions of (H+-ATPase) the total flux was not reduced, revealing a second cause for increased turnover number through increased membrane potential: respiration was increased showing that in E. coli, respiration and ATP synthesis are, in part, inversely coupled. Indeed, growth yield per O-2 decreased, suggesting significant leakage or slip at the high respiration rates and membrane potential found at low H+-ATPase concentrations, and explaining that growth yield may be increased by activating the H+-ATPase.