CONTROL ANALYSIS OF THE DEPENDENCE OF ESCHERICHIA-COLI PHYSIOLOGY ON THE H-ATPASE()

The H+-ATPase plays a central role in Escherichia coli free-energy tra nsduction and hence in E. coli physiology. We here investigate the ext ent to which this enzyme also controls the growth rate, growth yield, and respiratory rate of E. coli. We modulate the expression of the atp operon and determine the effect on said properties. When quantified i n terms of control coefficients, we find that, in the wild-type cell g rowing on glucose in minimal medium, this key enzyme (H+-ATPase) exert s virtually no control on growth rate (Absolute value of C < 0.01), a minor positive control on growth yield (C = 0.15), and a small but neg ative control on respiration rate (C = -0.25). The control the enzyme exerts on the consumption rate of the carbon and free-energy substrate is negative (C = -0.15). We also studied how the control coefficients themselves vary with the expression of the atp operon. As the level o f expression of the atp operon was reduced, the control exerted by the H+-ATPase on growth rate and growth yield increased slightly; the con trol on growth rate passed through a maximum (C = 0.1) and disappeared when the atp operon was not expressed at all, reflecting that with th is substrate there are alternative routes for ATP synthesis. At elevat ed levels of the H+-ATPase compared to the wild type, the control exer ted by the enzyme on growth rate became negative. The evolutionary con text of the absence of control by the atp operon on growth rate is dis cussed.