KINETICS AND MECHANISM OF LIVER ALCOHOL DEHYDROGENASE WITH PRIMARY AND SECONDARY ALCOHOLS AS SUBSTRATES
KINETICS AND MECHANISM OF LIVER ALCOHOL DEHYDROGENASE WITH PRIMARY AND SECONDARY ALCOHOLS AS SUBSTRATES
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DOI：
10.1042/bj1000034
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发表时间：
1966-01-01
影响因子：
4.1
通讯作者：
DICKINSON, FM
中科院分区：
文献类型：
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作者：
DALZIEL, K;DICKINSON, FM
1.肝醇脱氢酶与丙-2-醇和丁-2-醇的活性已被证实。与相应酮的活性较小。这些仲醇的氧化，和丙-1-醇和2-甲基丙-1-醇，并为减少丙醛和2-甲基丙醛的初始速率参数报告。还描述了与伯醇的底物抑制。2.所有伯醇和醛的数据满足Theorell-Chance机理的要求，但仲醇的数据不满足。一种机制，提供了从反应性三元复合物的辅酶或底物的解离的描述，并示出占伯和仲醇的初始速率数据，和同位素交换的结果为前者。与伯醇，快速的反应速率的三元复合物，和它的小的稳态浓度，导致符合初始速率数据的要求的Theorell-Chance机制。与仲醇，三元复合物反应更慢，其稳态浓度更大，因此辅酶从它的解离是限速与非饱和辅酶浓度。3.大浓度伯醇的底物抑制归因于酶、NADH和醇的流产复合物的形成，其中NADH比酶-NADH复合物解离得更慢。初始速率方程推导出完整的机制，其中包括一个二元酶-醇复合物和替代途径形成的反应三元复合物。在合适的条件下，根据通过两种途径的反应的相对速率，该机制还将提供双底物反应中的底物活化或底物抑制。
1. The activity of liver alcohol dehydrogenase with propan-2-ol and butan-2-ol has been confirmed. The activity with the corresponding ketones is small. Initial-rate parameters are reported for the oxidation of these secondary alcohols, and of propan-1-ol and 2-methylpropan-1-ol, and for the reduction of propionaldehyde and 2-methylpropionaldehyde. Substrate inhibition with primary alcohols is also described. 2. The requirements of the Theorell–Chance mechanism are satisfied by the data for all the primary alcohols and aldehydes, but not by the data for the secondary alcohols. A mechanism that provides for dissociation of either coenzyme or substrate from the reactive ternary complex is described, and shown to account for the initial-rate data for both primary and secondary alcohols, and for isotope-exchange results for the former. With primary alcohols, the rapid rate of reaction of the ternary complex, and its small steady-state concentration, result in conformity of initial-rate data to the requirements of the Theorell–Chance mechanisms. With secondary alcohols, the ternary complex reacts more slowly, its steady-state concentration is greater, and therefore dissociation of coenzyme from it is rate-limiting with non-saturating coenzyme concentrations. 3. Substrate inhibition with large concentrations of primary alcohols is attributed to the formation of an abortive complex of enzyme, NADH and alcohol from which NADH dissociates more slowly than from the enzyme–NADH complex. The initial-rate equation is derived for the complete mechanism, which includes a binary enzyme–alcohol complex and alternative pathways for formation of the reactive ternary complex. This mechanism would also provide, under suitable conditions, for substrate activation or substrate inhibition in a two-substrate reaction, according to the relative rates of reaction through the two pathways.