Competing peroxidase and oxidase reactions in scopoletin-dependent H2O2-initiated oxidation of NADH by horseradish peroxidase

Saikumar, P and Swaroop, A and Kurup, CKR and Ramasarma, T (1994) Competing peroxidase and oxidase reactions in scopoletin-dependent H2O2-initiated oxidation of NADH by horseradish peroxidase. In: Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1204 (1). pp. 117-123.

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Abstract

Addition of NADH inhibited the peroxidative loss of scopoletin in presence of horseradish peroxidase and H2O2 and decreased the ratio of scopoletin (consumed):H2O2 (added). Concomitantly NADH was oxidized and oxygen was consumed with a stoichiometry of NADH: O-2 of 2:1. On step-wise addition of a small concentration of H2O2 a high rate of NADH oxidation was obtained for a progressively decreasing time period followed by termination of the reaction with NADH:H2O2 ratio decreasing from about 40 to 10. The rate of NADH oxidation increased linearly with increase in scopoletin concentration. Other phenolic compounds including p-coumarate also supported this reaction to a variable degree. A 418-nm absorbing compound;d accumulated during oxidation of NADH. The effectiveness of a small concentration of H2O2 in supporting NADH oxidation increased in presence of SOD and decreased in presence of cytochrome c, but the reaction terminated even in their presence. The results indicate that the peroxidase is not continuously generating H2O2 during scopolerin-mediated NADH oxidation and that both peroxidase and oxidase reactions occur simultaneously competing for an active form of the enzyme.

Item Type:	Journal Article
Publication:	Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology
Publisher:	Elsevier science
Additional Information:	Copyright of this article belongs to Elsevier science.
Keywords:	Horseradish peroxidase; NADH oxidation; Oxidase-peroxidase reaction
Department/Centre:	Division of Biological Sciences > Biochemistry
Date Deposited:	25 Mar 2011 09:19
Last Modified:	25 Mar 2011 09:19
URI:	http://eprints.iisc.ac.in/id/eprint/36298

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