Halenaquinol, a natural cardioactive pentacyclic hydroquinone, interacts with sulfhydryls on rat brain Na(+),K(+)-ATPase.
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.
Gorshkova
I A
IA
Pacific Institute of Bioorganic Chemistry, Far East Branch of the Russian Academy of Sciences, 690022, Vladivostok, Russia. piboc@stl.ru
Gorshkov
B A
BA
Fedoreev
S A
SA
Stonik
V A
VA
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001551:Benz(a)Anthracenes / Q000494:pharmacology*; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D002414:Cations, Monovalent; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000378:metabolism*
D001551:Benz(a)Anthracenes; D002414:Cations, Monovalent; D004791:Enzyme Inhibitors; D013438:Sulfhydryl Compounds; C433468:halenaquinol; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase