Sulfonamides influence on the activity of thylakoid ATPase isolated from spinach chloroplasts

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. i50 (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 i50 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.