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Mechanism of aromatic hydroxylation *1, , *2, , *3: Properties of a model for pyridine nucleotide-dependent flavoprotein hydroxylases

Ravindranath, SD and Kumar, A Ashok and Kumar, R Prema and Vaidyanathan, CS and Rao, N Appaji (1974) Mechanism of aromatic hydroxylation *1, , *2, , *3: Properties of a model for pyridine nucleotide-dependent flavoprotein hydroxylases. In: Archives of Biochemistry and Biophysics, 165 (2). 478 -484.

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A model (NADH-phenazine methosulfate-O2) formally similar to pyridine nucleotide-dependent flavoprotein hydroxylases catalyzed the hydroxylation of several aromatic compounds. The hydroxylation was maximal at acid pH and was inhibited by ovine Superoxide dismutase, suggesting that perhydroxyl radicals might be intermediates in this process. The stoichiometry of the reaction indicated that a univalent reduction of oxygen was occurring. The correlation between the concentration of semiquinone and hydroxylation, and the inhibition of hydroxylation by ethanol which inhibited semiquinone oxidation, suggested the involvement of phenazine methosulfate-semiquinone. Activation of hydroxylation by Fe3+ and Cu2+ supported the contention that univalently reduced species of oxygen was involved in hydroxylation. Catalase was without effect on the hydroxylation by the model, ruling out H2O2 as an intermediate. A reaction sequence, involving a two-electron reduction of phenazine methosulfate to reduced phenazine methosulfate followed by disproportionation with phenazine methosulfate to generate the semiquinone, was proposed. The semiquinone could donate an electron to O2 to generate O2 which could be subsequently protonated to form the perhydroxyl radical.

Item Type: Journal Article
Publication: Archives of Biochemistry and Biophysics
Publisher: Elsevier Science
Additional Information: Copy right of this article belongs to Elsevier Science.
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 09 Jan 2010 05:11
Last Modified: 19 Sep 2010 05:49
URI: http://eprints.iisc.ac.in/id/eprint/24286

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