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

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

Received: 25 October 2018; Accepted: 13 December 2018

The present study of sulfite participation in the regulation of the chloroplast ATP-synthase complex can help to understand the mechanisms of acid rains toxic effects on the plant photosynthetic apparatus. The aim of the work was to study the effect of sulfite on Ca²⁺– and Mg²⁺-dependent ATP hydrolysis catalysed by coupling factor CF₁, exposed to preliminary short-term acid treatment. CF₁ was isolated from spinach chloroplasts (Spinacia oleracea L.). The latent ATPase activity of CF₁ was activated by sodium sulfite addition into incubation media. The rate of ATP hydrolysis was determined by the release of inorganic phosphate. In the presence of 25 mM exogenous sulfite  the Mg²⁺-dependent hydrolytic activity of CF₁ was increased 7-fold and Ca²⁺-dependent activity 3-fold compared to the control. Carbonic anhydrase inhibitors acetazolamide or ethoxyzolamide eliminated sulfite-induced stimulation of ATP hydrolysis. The sulfite stimulating effect on Ca²⁺– and Mg²⁺-ATPase activity was increased dramatically after incubation (5 min) of isolated CF₁ in a medium with pH 3.5 and its  subsequent transition to the alkali medium (pH 8.0). In this case, 1 mM sulfite-induced a 10-fold acceleration of ATP hydrolysis. Carbonic anhydrase specific inhibitors (50 μM) removed the sulfite effect. These data suggest that sulfite was able to replace bicarbonate in the CF₁ structure after the release of bound HCO₃^– during acid treatment.