Hydrogen tunneling in the flavoenzyme monoamine oxidase B.
Hydrogen tunneling in the flavoenzyme monoamine oxidase B.
复制标题
黄素酶单胺氧化酶 B 中的氢隧道。
DOI：
10.1021/bi00253a026
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发表时间：
1994
期刊：
影响因子：
2.9
通讯作者：
Klinman,JP
中科院分区：
文献类型：
--
作者：
Jonsson,T;Edmondson,DE;Klinman,JP
修订稿于 1994 年 10 月 3 日收到摘要：竞争性 kn/kj 和 kcJkj 动力学同位素对 8a-S-半胱氨酰黄素腺嘌呤二核苷酸 (FAD) 依赖性酶单胺氧化酶 B (MAO-B) 氧化对甲氧基苄胺的影响已作为温度的函数进行了测量。在 pH 7.5 时，与观察到的 ku/kj 和 kiJkj 同位素效应相关的指数表明限速步骤中存在温度依赖性变化。在较低温度（例如 2 C）下，从指数大小和单个同位素效应清楚地表明存在多个限速步骤（承诺）。非竞争性 kn/ku 同位素效应测量表明在 pH 9.0 至 6.0 之间观察到的同位素效应存在趋势，同位素效应在较低 pH 值下增强。因此，在 pH 6.1 下，将初级和次级 kn/k- 和 ku/kj 同位素效应测量为温度的函数。在 10-43℃ 范围内，初级和次级 kn/kj 和 kjk-t 的相关指数分别为 3.13±0.04 和 2.36±0.13，并且不随温度系统性地变化。这些数据表明，承诺（如果存在）在该温度范围内保持不变。观察到的主要同位素效应的温度依赖性给出了阿累尼乌斯前因子的比率值：0.13±0.03 (Ah/At) 和 0.52±0.05 (Ad/At)。这两个值都远低于在反应坐标没有隧道效应的情况下预测的下限，表明该反应中发生了氘和氕隧道效应。不能严格排除与温度无关的承诺贡献的存在；然而，这种承诺对观察到的 Ah/At 和 Ad/At 值的影响很小。
Revised Manuscript Received October 3, 1994® abstract: Competitive kn/kj and kcJkj kinetic isotope effects on p-methoxybenzylamine oxidation by the 8a-S-cysteinyl flavin adenine dinucleotide (FAD)-dependent enzyme monoamine oxidase B (MAO-B) have been measured as a function of temperature. At pH 7.5, exponents relating observed ku/kj and kiJkj isotope effects indicate the presence of a temperature-dependent change in rate-limiting step. At lower temperature (eg, 2 C), the presence of multiple rate-limiting steps (commitments) is clearly indicated from the size of the exponent and individual isotope effects. Noncompetitive kn/ku isotope effect measurements indicate a trend in observed isotope effects between pH 9.0 and 6.0, with isotope effects increasing at lower pH. Primary and secondary kn/k-and ku/kj isotope effects were therefore measured as a function of temperature at pH 6.1. Exponents relating primary and secondary kn/kj and kjk-t in the 10—43 C range are 3.13±0.04 and 2.36±0.13, respectively, and do not systematically change with temperature. These data indicate that commitments, if present, remain constant across this temperature range. The temperature dependence of the observed primary isotope effects givesvalues for the ratios of Arrhenius prefactors of 0.13±0.03 (Ah/At) and 0.52±0.05 (Ad/At). Both values are well below the lower limits predicted in the absence of tunneling contributions to the reaction coordinate, indicating that both deuterium and protium tunneling take place in this reaction. The presence of a temperature independent commitment contribution cannot be rigorously ruled out; however, the effect of such a commitment on the observed Ah/At and Ad/At values is shown to be quite small.