Regulation of the cytoplasmic pH by a proton-translocating ATPase in Streptococcus faecalis (faecium). A computer simulation.

Earlier work from this laboratory led to the proposal that the cytoplasmic pH of streptococcal cells is regulated solely by changes in the amount and activity of a proton-translocating ATPase, F1F0 complex [Kobayashi, H., Suzuki, T. & Unemoto, T. (1986) J. Biol. Chem. 261, 627-630]. We have now examined the proposal with the aid of computer simulation. We find that an increase in the amount of the H+-ATPase is necessary for pH regulation and is sufficient to maintain a constant steady-state cytoplasmic pH. An increase in H+-ATPase activity is insufficient by itself to maintain a constant cytoplasmic pH, but suppresses the initial fluctuation of the pH. When both variations were allowed, the simulated cytoplasmic pH remained constant despite large perturbations, suggesting that this regulatory system has ample capacity to compensate for pH changes. The present work shows that a computer simulation is a useful way to examine a model for biological regulatory system; application of the simulation to other regulatory systems is discussed.