Adenine nucleotides regulate the functional transition in mitochondrial H+-ATPase and the kinetic behaviour of its ATP-synthetase form.

The kinetics of the SMP-catalyzed Pi-ATP exchange and oxidative phosphorylation was studied at variable [MgATP] + + [MgADP] and [MgATP]/[MgADP]. The existence on F1 of a center with a low affinity was demonstrated (KM = 0.4-2.7 mM). Saturation of this center with the Mg2+-complex of one of the nucleotides is obligatory for H+-ATPase to exhibit its ATP synthetase activity. It was found that with a decrease of [MgATP]/[MgADP] the lag periods, tau, of the reactions and KM(Pi) also show a decrease. Besides, in the Pi-ATP exchange reactions delta microH+ (steady-state) diminishes and SMP coupling is enhanced (the Vhydr/Vsynth ratio is decreased). Preincubation of SMP with MgADP eliminates the lags but does not affect the course of the steady-state reaction. It is concluded that F1 when bound to MgATP or MgADP changes to a "more" or "less coupled" conformational state, thus determining the rate of conversion to the ATP-synthetase functional state (ko = tau-1), the threshold potential of this conversion and the kinetic behaviour of ATP-synthetase (KM for Pi).