EXPERIMENTAL-DETERMINATION OF CONTROL BY THE H-ATPASE IN ESCHERICHIA-COLI()

Strains carrying deletions in the atp genes, encoding the H+-ATPase, w ere unable to grow on nonfermentable substrates such as succinate, whe reas with glucose as the substrate the growth rate of an atp deletion mutant was surprisingly high (some 75-80% of wild-type growth rate). T he rate of glucose and oxygen consumption of these mutants was increas ed compared to the wild-type rates. In order to analyze the importance of the H+-ATPase at its physiological level, the cellular concentrati on of H+-ATPase was modulated around the wild-type level, using geneti cally manipulated strains. The control coefficient by the H+-ATPase wi th respect to growth rate and catabolic fluxes was measured. Control o n growth rate was absent at the wildtype concentration of H+-ATPase, i ndependent of whether the substrate for growth was glucose or succinat e. Control by the H+-ATPase on the catabolic fluxes, including respira tion, was negative at the wild-type H+-ATPase level. Moreover, the tur nover number of the individual H+-ATPase enzymes increased as the H+-A TPase concentration was lowered. The negative control by the H+-ATPase on catabolism may thus be involved in a homeostatic control of ATP sy nthesis and, to some extent, explain the zero control by the H+-ATPase on E. coli growth rate.