A. P. Khomochkin, O. B. Onoiko, A. V. Semenikhin, O. K. Zolotareva

M. G. Kholodhy Institute of Botany, National Academy of Sciences of Ukraine, Kyiv;
e-mail: membrana@ukr.net

The aim of the work was to study the reverse pH-dependent regulation of the enzymatic activity of the catalytic part of ATP synthase (EC 3.6.3.14) of chloroplast – coupling factor CF₁. It was shown that the short-term incubation of isolated CF₁ in the media with pH 4.5 or 3.5 leads to inactivation of Ca²⁺-ATPase, which is rapidly (t_1/2 ~ 1 min) restored in the medium containing 0.5-10 mM bicarbonate at pH 7.8. After acid treatment, the rate of Mg²⁺-ATPase reaction was also stimulated in the presence of 1 mM bicarbonate (рН 7.8; 37 °С). The increase in Ca²⁺– and Mg²⁺-АТР activity of CF₁ associated with the addition of NaHCO₃ solution was completely eliminated after the introduction of 50 mM acetazolamide – a specific inhibitor of carbonic anhydrase. The obtained results suggest the existence of the bound bicarbonate in the CF₁ structure, which apparently participates in proton transfer.