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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. K e y w o r d s: spinach chloroplasts, CF1-ATPase, ATP hydrolysis, pH-dependence, sulfite, acetazolamide, ethoxyzolamide.

Influence of sulfite on ATPase activity of coupling factor CF(1) isolated from spinach chloroplasts