the enzyme rhodanese (thiosulfate: cyanide sulfurtransferase) is a ubiquitous enzyme and its activity ispresent in all living organisms. many functions including cyanide detoxification, formation of iron-sulfurcenters and participation in energy metabolism have been attributed to this enzyme. the enzyme catalyzesthe transfer of a sulfur atom from sulfane containing compounds (such as thiosulfat...

The importance of two of the thiol groups of yeast triosephosphate dehydrogenase for its activity haa been shown by the abolition of activity and diphosphopyridine nucleotide binding by the addition of 2 equivalents of p-chloromercuribenzoate (PCMB) (1, 2). The reaction of methyl mercury nitrate with this enzyme has been found to be anomalous in the sense that this mercury compound, unlike PCMB...

Approximately 90% of the total tyrosine hydroxylase activity of bovine adrenal medulla homogenates was localized in the particulate fraction of the homogenate. The particulate enzyme was solubilized by incubation with trypsin, and the solubilized enzyme was partially purified. This enzyme was found to behave like the tyrosine hydroxylase which had been purified from the supernatant fraction by ...

When chicken liver dihydrofolate reductase reacts with an excess of sodium tetrathionate, 1 mol of thiosulfate becomes covalently attached to the single sulfhydryl group of the enzyme. The identity of the thiosulfate was established by obtaining 1:l binding independently with both innerand outer-labeled [36S]tetrathionate. The thiosulfate form of the enzyme has 5to 10-fold more activity than n...

The effect of cupric ions on the activity, fluorescence, and absorbance, and on the sulfhydryl and flavin adenine dinucleotide contents, of lipoyl dehydrogenase has been examined. The changes take place in two phases during the reaction of the enzyme with copper ions. In the first phase, the lipoic activity of the enzyme decreases to about 10% of its initial value, while its diaphorase activity...

Purified ferrochelatase (protoheme ferrolyase; EC 4.99.1.1) from the bacterium Rhodopseudomonas sphaeroides was examined to determine the roles of cationic and sulfhydryl residues in substrate binding. Reaction of the enzyme sulfhydryl residues with N-ethylmaleimide or monobromobimane resulted in a rapid loss of enzyme activity. Ferrous iron, but not porphyrin substrate, had a protective effect...

In earlier work with partially purified preparations, we have examined inhibitory processes (l-3) and substrate specificity (4, 5) of n-amino acid oxidase. With availability of a highly purified crystallized enzyme prepared from hog kidney (6), an investigation of certain aspects of enzymatic mechanism has been initiated. In the present study enzymatic activity was observed to be depressed as a...

Incubation of maize (Zea mays) leaf NADP-malic enzyme with monofunctional and bifunctional N-substituted maleimides results in an irreversible inactivation of the enzyme. Inactivation by the monofunctional reagents, N-ethylmaleimide (NEM) and N-phenylmaleimide, followed pseudo-first-order kinetics. The maximum inactivation rate constant for phenylmaleimide was 10-fold higher than that for NEM, ...

Phosphoribosylpyrophosphate synthetase from Salmonella typhimurium contains four cysteine residues per subunit. Three of these react readily with 5, 5'-dithiobis(2-nitrobenzoic acid) (DTNB), forming an active derivative with kinetic and physical properties similar to the native enzyme, but one reacts only under denaturing conditions. Stoichiometric amounts of KMnO4 inactivate the DTNB-treated e...