Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rate of rhodanese inactivation by 2,4,6-trinitrobenzenesulphonate is increased in the presence of diethylbarbiturate in the reaction medium. A "rate saturation effect" indicates the formation of a rhodanese-diethylbarbiturate complex, prior to modification-induced enzyme inactivation. The dissociation constant of this complex is 19.0 mM. Diethylbarbiturate has no effect on the trinitrophenylation rate of the free amino groups of rhodanese. When rhodanese modification, in the presence of diethylbarbiturate in the reaction medium, is carried out by the use of a 2,4,6-trinitrobenzenesulphonate concentration much lower than the concentration of rhodanese modifiable amino groups, reaction stoichiometry indicates that 3 to 5 moles of rhodanese are rendered inactive for each mole of 2,4,6-trinitrobenzenesulphonate utilized. This finding indicates the existence of a chain-reaction type mechanism of rhodanese inactivation.
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PMID:Diethylbarbiturate potentiation of 2,4,6-trinitrobenzenesulphonate-induced rhodanese inactivation. 209 68

Sulfhydryl groups of bovine liver rhodanese (thiosulfate: cyanide sulfurtransferase, EC 2.8.1.1) were modified by treatment with tetrathionate. There was a linear relationship between loss of enzyme activity and the amount of tetrathionate used. At a ratio of one tetrathionate per mole of rhodanese, 100% of enzyme activity was lost in the sulfur-free E-form as compared with a 70% loss for the sulfur-containing ES-form of the enzyme. Addition of up to a 100-fold molar excess of tetrathionate to ES gave no further inactivation. Addition of cyanide to the maximally inactivated ES-tetrathionate complex gave complete loss of activity. Kinetic studies of maximally inactivated ES and partially inactivated E gave Km (Ks) values that were essentially the same as native enzyme, indicating that the active enzyme, in all cases, bound thiosulfate similarly. Reactivation was faster with the ES-form than with the E-form. The substrate, thiosulfate, could reactivate the enzyme up to 70% in 1 h with ES as compared to 24 h with E. Tetrathionate modification of rhodanese could be correlated with the changes in intrinsic fluorescence and with the binding of the active site reporter 2-anilinonaphthalene-8-sulfonic acid (2,8-ANS). Circular dichroism spectra of the protein suggested increased ordered secondary structure in the protein after reaction with tetrathionate. Cadmium chloride and phenylarsine oxide totally inactivated the enzyme at levels usually associated with their effect on enzymes containing vicinal sulfhydryl groups. Further, cadmium inhibition could be reversed by EDTA. Tetrathionate modification of rhodanese may proceed through the formation of sulfenylthiosulfate intermediates at sulfhydryl groups, close to but not identical with the active-site sulfhydryl group, which then can react further with the active-site sulfhydryl group to form disulfide bridges.
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PMID:Chemical modification of bovine liver rhodanese with tetrathionate: differential effects on the sulfur-free and sulfur-containing catalytic intermediates. 346 49

The reaction of sulfur-free rhodanese with 5-5'-dithio-bis (2-nitrobenzoic acid) produces a modified enzyme with 35% of residual activity. The resulting enzyme derivative has 1.6 moles of thionitrobenzoate/mole of enzyme bound to sulfhydryl groups of rhodanese. Determination of free sulfhydryl groups of this derivative shows that during the reaction with 5-5'-dithio-bis (2-nitrobenzoic acid) oxidative formation of an intramolecular disulfide bridge between two sulfhydryl groups of rhodanese occurs. Cyanolysis of the modified enzyme produces an enzyme-thiocyano derivative which partially beta-eliminates with release of thiocyanate. The cleavage of disulfide bonds present in the enzyme-thionitrobenzoate adduct using labeled cyanide shows an incorporation of radioactivity in the protein higher than would be expected. An electrostatic bond between cyanide and positively charged groups of the enzyme is suggested. Most of bound cyanide is released when samples are acidified for protein hydrolysis. In these conditions the thiocyanoalanine residue cyclizes to form 2-iminothiazolidine-4-carboxylic acid.
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PMID:Studies of cyanolysis of the rhodanese-thionitrobenzoate complex. 693 99