title: Differential effect of thiol oxidants on the chloroplast H+-ATPase in the light and in the dark.
abstract: The effect of thiol oxidants on the light-activated H+-ATPase has been studied in freshly broken and intact chloroplasts. The following observations were made: (i) in chloroplasts which are osmotically shocked after light activation, ferricyanide stimulates the deactivation of the enzyme in the dark, but has little effect in the light; (ii) similarly, o-iodosobenzoate is a most efficient deactivator of the ATPase in intact chloroplasts in the dark but not in the light; (iii) the activated ATPase becomes sensitive to oxidants in the light upon the addition of an uncoupler; (iv) the oxidant-induced deactivation in the dark dominates the stabilizing effect of pyrophosphate or ADP plus Mg2+; (v) full deactivation of the ATPase by dark adaptation or by oxidants does not affect the rate of photophosphorylation under saturating conditions. A model is suggested in which two kinds of conformational changes are involved in the regulation of the ATPase: those induced by the trans-membrane-proton gradient and those by oxidation-reduction of the enzyme. These changes result in the preferential interaction with thiol reductants in the light but with thiol oxidants in the dark.
authors.forename: Y
authors.initials: Y
authors.lastname: Shahak
mesh_terms: D002736:Chloroplasts / Q000201:enzymology*; D003624:Darkness; D004789:Enzyme Activation / Q000528:radiation effects; D005292:Ferricyanides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007463:Iodobenzoates / Q000494:pharmacology; D008027:Light; D009550:Nigericin / Q000494:pharmacology; D009997:Osmotic Pressure; D010084:Oxidation-Reduction; D010944:Plants / Q000201:enzymology; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000528:radiation effects; D013438:Sulfhydryl Compounds / Q000378:metabolism*
chemical_list: D005292:Ferricyanides; D007463:Iodobenzoates; D013438:Sulfhydryl Compounds; C007931:hexacyanoferrate III; C008154:2-iodosobenzoic acid; D006180:Proton-Translocating ATPases; D009550:Nigericin