RESUMO
The kinetics of oxidative phosphorylation catalyzed by bovine heart submitochondrial particles was studied in a range of MgATP and MgADP concentrations from 0.3 to 10 mM. It is shown that, at a low uncoupler concentration (0.9 microM of tetrachlorotrifluoromethylbenzimidazole, the lag period of the reaction increases from 12 s to 2-3 min, and KM for Pi increases severalfold; the value of Vmax remains practically unchanged. Increasing the [MgATP]/[MgADP] concentration ratio, with their total concentration being unchanged, leads to similar changes in the kinetics of oxidative phosphorylation. The value of delta pH generated on the membrane of AS particles at delta microH+ = 60 delta pH was measured using 9-aminoacridine. It was found that the electrochemical potential of H+ ions shows the same thermodynamic shift in the reaction of energy-dependent Pi -ATP exchange throughout the [MgATP]/[MgADP] concentration range studied, from 0.1 to 10: the synthesis on the ATP molecule is provided by the transmembrane transfer of two H+ ions. It was shown that the binding of ATP and/or ADP in the allosteric site, whose saturation is necessary for the functioning of ATP synthase, occurs with equal constants, 1-2 mM. It is concluded that the lag period in the synthesis of ATP indicates the monomolecular transition ATP hydrolase-->ATP sysnthase, which comes about by the action of transmembrane potential. The binding of MgADP or MgATP renders the enzyme structure "more coupled" or "less coupled", respectively. Structural distinctions manifest themselves in a kinetically different behavior of mitochondrial ATP synthase at [MgATP] > [MgADP] and [MgATP] < [MgADP] and do not suggest futile leakage of H+ through the membrane.
