Proton transport-coupled unisite catalysis by the H(+)-ATPase from chloroplasts.

Proton transport-coupled unisite catalysis was measured with the H(+)-ATPase from chloroplasts. The reaction was measured in the ATP hydrolysis direction under deenergized conditions and in the ATP synthesis direction under energized conditions. The equilibrium constant of the enzyme does not change upon energization, whereas the dissociation constants of substrates and products change by orders of magnitude. This indicates that the Gibbs free enthalpy derived from proton translocation is used to change binding affinities of substrates and products, and this results in synthesis of free ATP.