Saikumar P, Swaroop A, Kurup C K, Ramasarma T
Department of Biochemistry, Indian Institute of Science, Bangalore.
Biochim Biophys Acta. 1994 Jan 11;1204(1):117-23. doi: 10.1016/0167-4838(94)90040-x.
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: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.
在辣根过氧化物酶和过氧化氢存在的情况下，添加烟酰胺腺嘌呤二核苷酸（NADH）可抑制东莨菪素的过氧化损失，并降低东莨菪素（消耗）与过氧化氢（添加）的比例。同时，NADH被氧化，氧气被消耗，NADH与氧气的化学计量比为2:1。逐步添加低浓度的过氧化氢时，在逐渐缩短的时间段内可获得较高的NADH氧化速率，随后反应终止，NADH与过氧化氢的比例从约40降至10。NADH的氧化速率随东莨菪素浓度的增加呈线性增加。包括对香豆酸在内的其他酚类化合物也在不同程度上支持该反应。在NADH氧化过程中积累了一种在418纳米处有吸收的化合物。在超氧化物歧化酶（SOD）存在时，低浓度过氧化氢支持NADH氧化的效果增强，而在细胞色素c存在时则降低，但即使在它们存在的情况下反应仍会终止。结果表明，在东莨菪素介导的NADH氧化过程中，过氧化物酶不会持续产生过氧化氢，过氧化物酶和氧化酶反应同时发生，竞争酶的活性形式。
