TY - JOUR
T1 - Competing peroxidase and oxidase reactions in scopoletin-dependent H2O2-initiated oxidation of NADH by horseradish peroxidase
AU - Saikumar, P.
AU - Swaroop, A.
AU - Ramakrishna Kurup, C. K.
AU - Ramasarma, T.
N1 - Funding Information:
The financial assistance by the Department of Science and Technology, Government of India is acknowledged. TR is an emeritus scientist of the Council of Scientific and Industrial Research, New Delhi.
PY - 1994/1/11
Y1 - 1994/1/11
N2 - Addition of NADH inhibited the peroxidative loss of scopoletin in presence of horseradish and H2O2 and decreased the ratio of scopoletin (consumed):H2O2 (added). Concomitantly NADH was oxidized and oxygen was consumed with a stoichiometry of NADH:O2 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 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 scopoletin-mediated NADH oxidation and that both peroxidase and oxidase reactions occur simultaneously competing for an active form of the enzyme.
AB - Addition of NADH inhibited the peroxidative loss of scopoletin in presence of horseradish and H2O2 and decreased the ratio of scopoletin (consumed):H2O2 (added). Concomitantly NADH was oxidized and oxygen was consumed with a stoichiometry of NADH:O2 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 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 scopoletin-mediated NADH oxidation and that both peroxidase and oxidase reactions occur simultaneously competing for an active form of the enzyme.
KW - Horseradish peroxidase
KW - NADH oxidation
KW - Oxidase-peroxidase reaction
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U2 - 10.1016/0167-4838(94)90040-X
DO - 10.1016/0167-4838(94)90040-X
M3 - Article
C2 - 8305468
AN - SCOPUS:0027954662
SN - 1570-9639
VL - 1204
SP - 117
EP - 123
JO - BBA - Protein Structure
JF - BBA - Protein Structure
IS - 1
ER -