Halenaquinol, a natural cardioactive pentacyclic hydroquinone, interacts with sulfhydryls on rat brain Na(+),K(+)-ATPase |
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Authors: | Gorshkova I A Gorshkov B A Fedoreev S A Stonik V A |
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Institution: | Pacific Institute of Bioorganic Chemistry, Far East Branch of the Russian Academy of Sciences, 690022, Vladivostok, Russia. piboc@stl.ru |
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Abstract: | Halenaquinol inhibited the partial reactions of ATP hydrolysis by rat brain cortex Na(+),K(+)-ATPase, such as 3H]ATP binding to the enzyme, Na(+)-dependent front-door phosphorylation from gamma-(33)P]ATP, and also Na(+)- and K(+)-dependent E(1)<-->E(2) conformational transitions of the enzyme. Halenaquinol abolished the positive cooperativity between the Na(+)- and K(+)-binding sites on the enzyme. ATP and sulfhydryl-containing reagents (cysteine and dithiothreitol) protected the Na(+),K(+)-ATPase against inhibition. Halenaquinol can react with additional vital groups in the enzyme after blockage of certain sulfhydryl groups with 5,5'-dithio-bis-nitrobenzoic acid. Halenaquinol inhibited 3H]ouabain binding to Na(+),K(+)-ATPase under phosphorylating and non-phosphorylating conditions. Binding of fluorescein 5'-isothiocyanate to Na(+),K(+)-ATPase and intensity of fluorescence of enzyme tryptophanyl residues were decreased by halenaquinol. We suggest that interaction of halenaquinol with the essential sulfhydryls in/or near the ATP-binding site of Na(+),K(+)-ATPase resulted in a change of protein conformation and subsequent alteration of overall and partial enzymatic reactions. |
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