title: N-Ethylmaleimide inhibition of the catalytic activities of the Dunaliella salina coupling factor 1 (CF1) and the restoration of the inhibition of the CF1 ATPase activity by N-ethylmaleimide.
abstract: The sensitivity of the catalytic activities of the D. salina chloroplast coupling factor 1 (CF1) to chemical modification by N-ethylmaleimide has been investigated. When D. salina thylakoid membranes are treated with N-ethylmaleimide, both photophosphorylation and the inducible CF1 ATPase activity are partially (approx. 60%) inhibited. The inhibition of both activities does not require the presence of a proton-motive force, and the inhibition of photophosphorylation is directly related to the N-ethylmaleimide-covalent modification of CF1 as shown by the time-course for the inhibition and the maximal extent of inhibition. Treatment of the purified, latent, D. salina CF1 with low concentrations of N-ethylmaleimide also results in the partial (approx. 60%) inhibition of the inducible ATPase activity (I50 approximately 50 microM). The inhibition does not require the presence of the chemical modifier during the activation of the enzyme. N-ethylmaleimide-induced inhibition of the ATPase activity of either membrane-bound or solubilized CF1 is partially reversed by either prolonged incubation at low concentrations of N-ethylmaleimide or short incubation times at high concentrations of N-ethylmaleimide. The results are interpreted as indicating multiple binding sites on the D. salina CF1 that have different rates of reactivity with N-ethylmaleimide. Those sites (or site) that react rapidly with N-ethylmaleimide cause(s) an inhibition of both ATP synthase and ATPase activities, whereas those sites (or site) that react more slowly partially restore(s) the original ATPase activity. The effects of N-ethylmaleimide on the catalytic activity of D. salina CF1 are probably mediated by N-ethylmaleimide-induced conformational changes of the enzyme.
authors.forename: S
authors.initials: S
authors.lastname: Selman-Reimer
authors.forename: R J
authors.initials: RJ
authors.lastname: Duhe
authors.forename: B R
authors.initials: BR
authors.lastname: Selman
mesh_terms: D000460:Chlorophyta / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D005033:Ethylmaleimide / Q000494:pharmacology*; D010766:Phosphorylation; D010788:Photosynthesis / Q000187:drug effects; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors*; D013997:Time Factors
chemical_list: D006180:Proton-Translocating ATPases; D005033:Ethylmaleimide