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Studies on the sarcoplasmic reticulum (Ca²+ + Mg²+) ATPase / Bousselsela, Haoues 

Public ISBD Titre : Studies on the sarcoplasmic reticulum (Ca²+ + Mg²+) ATPase Type de document : texte imprimé Auteurs : Bousselsela, Haoues, Auteur ; Thomas, E. W., Directeur de thèse Editeur : University of Salford Année de publication : 1992 Importance : 216 f. Présentation : ill. Format : 27 cm. Note générale : Thèse d’État : Biologie : Salford, University of Salford : 1992 Bibliogr. f. 217 - 231 Langues : Anglais (eng) Mots-clés : ATPase  enzyme  ;  Inhibition  labelling  ;  Carbodiimides  ;  Phenolic  compounds  ;  Cyclopiazonic Index. décimale : D000992 Résumé : Sarcoplasmic reticulum vesicles were isolated from rabbit hindleg and back muscle, yielding 120-130 mg SR protein using 200-300 g muscle, and resulting in a(Ca²+ + Mg²+)- ATPase with specific activity of 13-15 µmol/mg/min. NCD-4 and NCD-5 were shown to be efficient as fluorescent probes of (Ca²+ + Mg²+)-ATPase. Both carbodiimides inhibited the enzyme activity only in the absence of Ca²+ (specificially labelled vesicles): inclusion of Ca²+(1 mM) protects against inhibition. A series of phenolic compounds showed an inhibitory action on (Ca²+ + Mg²+)-ATPase activity in the following order: bis (2-hydroxy-3, 5-methylphenyl) methane> 3(4'-hydroxyphenyl) decane and (4'-hydroxyphenyl-n-heptylketone> 1,1 bis(4-hydroxyphenyl) cyclohexane> 4,4'-isopropylidene diphenol> bis (2-hydroxyphenyl)methane> 4,4'-hydroxybenzophenone> 4-methoxyphenyl-n-heptylketone. No good correlation was obtained between the ability of phenols to inhibit (Ca²+ + Mg²+)-ATPase activity and the ability to perturb a Ca²+ -induced fluorescence quench leading to the suggestion that phenolic compounds affect other steps in the catalytic cycle besides those associated with Ca²+ -binding. Cyclopiazonic acid was found to be an excellent inhibitor whereas its analogs "A" and "B" showed no effect on (Ca²+ + Mg²+)-ATPase activity: this may possibly ascribed to the high ATP concentration used in the essay. All flavanoids examined exhibited an inhibitory effect on the (Ca²+ + Mg²+)-ATPase activity in the following order: robinetin> quercetin> luteolin> fisetin>galangin> rhamentin. This group of compounds required for their potency a 7-hydroxyl group but in the presence of additional hydroxyl groups at 3'4' and 5' positions. Hydroxyl groups 3 and 5 seem do not participate in the inhibitory potency of the flavonoids. Quercetin was found to inhibit (Ca²+ + Mg²+)-ATPase activity reversibly with half-maximal inhibition at 10 µM. This inhibition showed a pH dependence with the doses of quercetin being significantly lower at pH 8 than at pHs 7 and 6.4. Also this inhibition can be removed by affinity chromatography on a Reactive Red-120 agarose matrix. Irradiation with light of wavelengths> 350 nm of a mixture of (Ca²+ + Mg²+)-ATPase and quercetin led to covalent inhibition of enzyme, whose extent is related to quercetin and enzyme concentrations. Pre-irradiation of quercetin followed by incubation at room temperature for 30 min with (Ca²+ + Mg²+)-ATPase did not inhibit enzyme. The possibility of photolabelling of the enzyme is dicussed. Studies on the sarcoplasmic reticulum (Ca²+ + Mg²+) ATPase [texte imprimé] / Bousselsela, Haoues, Auteur ; Thomas, E. W., Directeur de thèse . - [S.l.] : University of Salford, 1992 . - 216 f. : ill. ; 27 cm. Thèse d’État : Biologie : Salford, University of Salford : 1992 Bibliogr. f. 217 - 231 Langues : Anglais (eng) Mots-clés : ATPase  enzyme  ;  Inhibition  labelling  ;  Carbodiimides  ;  Phenolic  compounds  ;  Cyclopiazonic Index. décimale : D000992 Résumé : Sarcoplasmic reticulum vesicles were isolated from rabbit hindleg and back muscle, yielding 120-130 mg SR protein using 200-300 g muscle, and resulting in a(Ca²+ + Mg²+)- ATPase with specific activity of 13-15 µmol/mg/min. NCD-4 and NCD-5 were shown to be efficient as fluorescent probes of (Ca²+ + Mg²+)-ATPase. Both carbodiimides inhibited the enzyme activity only in the absence of Ca²+ (specificially labelled vesicles): inclusion of Ca²+(1 mM) protects against inhibition. A series of phenolic compounds showed an inhibitory action on (Ca²+ + Mg²+)-ATPase activity in the following order: bis (2-hydroxy-3, 5-methylphenyl) methane> 3(4'-hydroxyphenyl) decane and (4'-hydroxyphenyl-n-heptylketone> 1,1 bis(4-hydroxyphenyl) cyclohexane> 4,4'-isopropylidene diphenol> bis (2-hydroxyphenyl)methane> 4,4'-hydroxybenzophenone> 4-methoxyphenyl-n-heptylketone. No good correlation was obtained between the ability of phenols to inhibit (Ca²+ + Mg²+)-ATPase activity and the ability to perturb a Ca²+ -induced fluorescence quench leading to the suggestion that phenolic compounds affect other steps in the catalytic cycle besides those associated with Ca²+ -binding. Cyclopiazonic acid was found to be an excellent inhibitor whereas its analogs "A" and "B" showed no effect on (Ca²+ + Mg²+)-ATPase activity: this may possibly ascribed to the high ATP concentration used in the essay. All flavanoids examined exhibited an inhibitory effect on the (Ca²+ + Mg²+)-ATPase activity in the following order: robinetin> quercetin> luteolin> fisetin>galangin> rhamentin. This group of compounds required for their potency a 7-hydroxyl group but in the presence of additional hydroxyl groups at 3'4' and 5' positions. Hydroxyl groups 3 and 5 seem do not participate in the inhibitory potency of the flavonoids. Quercetin was found to inhibit (Ca²+ + Mg²+)-ATPase activity reversibly with half-maximal inhibition at 10 µM. This inhibition showed a pH dependence with the doses of quercetin being significantly lower at pH 8 than at pHs 7 and 6.4. Also this inhibition can be removed by affinity chromatography on a Reactive Red-120 agarose matrix. Irradiation with light of wavelengths> 350 nm of a mixture of (Ca²+ + Mg²+)-ATPase and quercetin led to covalent inhibition of enzyme, whose extent is related to quercetin and enzyme concentrations. Pre-irradiation of quercetin followed by incubation at room temperature for 30 min with (Ca²+ + Mg²+)-ATPase did not inhibit enzyme. The possibility of photolabelling of the enzyme is dicussed.

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