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 Ca 2+-and Mg 2+-dependent AtP hydrolysis catalysed by coupling factor CF 1 , exposed to preliminary short-term acid treatment. CF 1 was isolated from spinach chloroplasts (Spinacia oleracea L.). The latent ATPase activity of CF 1 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 Mg 2+-dependent hydrolytic activity of CF 1 was increased 7-fold and ca 2+-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 Ca 2+and Mg 2+-ATPase activity was increased dramatically after incubation (5 min) of isolated CF 1 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 CF 1 structure after the release of bound hcO 3 during acid treatment.

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the effect of two water-soluble sulfonamides: aromatic 4-aminobenzenesulfonamide (Sa) and aliphatic trifluoromethylsulfonamide (tFmSa) on the latent and stimulated atPase activity of the catalytic part of the thylakoid atP synthase isolated from spinach (Spinacia oleracea l.) chloroplasts was studied. three methods of atPase activity stimulation were applied in the work: brief heating of the enzyme at 62 °С; incubation with 20% methanol; 25 mm sodium sulfite adding to the reaction medium. tFmSa effectively inhibited the atPase activity of the enzyme at all types of activation. i 50 (tFmSa) value for was found to be about 5 μm in the case of enzyme heat treatment and 1 μm in the case of enzyme activation with sulfite or methanol. Sa did not affect atPase activity at stimulation with sulfite and inhibited with i 50 about 50 μm at stimulation by heating or methanol. no effect of Sa on latent enzyme activity was observed, while tFmSa was shown to activate latent atPase by about 6 times. the data obtained showed that both sulfonamide compounds, known as carbonic anhydrase inhibitors, are able to modify the activity of chloroplast atPase.

3.2 billion years ago primordial cyanobacteria started to produce molecular oxygen f r o m water through oxygenic, plant-type photosynthesis thereby transforming an essentially anaerobic into a n aerobic biosphere a n d atmosphere, thus forming the roots of all higher f o r m s of life, shaping the earth to w h a t we are used to now. As a logical consequence of the first production of free oxygen the cyanobacteria finally transformed their photosynthetic into a respiratory system with a n aerobic respiratory chain (conversion hypothesis). During the last three decades in my laboratory, respiratory properties of thirty-three species a n d strains of cyanobacteria were investigated. In all cases it was found, i.a. that isolated plasma as well as thylakoid membranes contained a fully functional aa3-type cytochrome-c oxidase very similar to its much better known counterpart in Paracoccus denitrificans, or even the mitochondrial enzyme, in bioenergetic, biochemical and genetic respects which will be discussed in some more detail in the present presentation (see G.A. Peschek, 1996: Biochem. SOC. Trans. 24,729-733, and BBA 1275,27-32).