Numerical simulation of uni-site and bi-site ATP-hydrolysis catalyzed by the membrane-bound H(+)-ATPase from chloroplasts.

The kinetics of ATP-hydrolysis catalyzed by the H(+)-ATPase from chloroplasts was described by an enzyme kinetic model where either one (uni-site catalysis) or two (bi-site catalysis) sites are operating. Numerical simulations are carried out with the software package LARKIN using measured rate constants as a basis. When the ATP-concentration is increased up to 20 nM (at 20 nM enzyme concentration) a change from uni-site to bi-site catalysis occurs at about 7 nM. The measured effective rate constants change by a factor two. However, the calculated rate constants for the second site are drastically increased.