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首页> 外文期刊>Biochemistry >Substrate determinants of the course of tartrate dehydrogenase-catalyzed reactions.
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Substrate determinants of the course of tartrate dehydrogenase-catalyzed reactions.

机译：酒石酸脱氢酶催化反应过程的底物决定因素。

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摘要

The substrate specificity of tartrate dehydrogenase has been probed using a series of alternative substrates to identify the molecular interactions which determine whether a particular substrate undergoes enzyme-catalyzed decarboxylation or not. A series of 3-substituted malate analogs, in which F, Cl, Br, I, SH, or NH2 substituents were placed at the 3R- or 3S-position, was prepared, and the product resulting from the action of tartrate dehydrogenase on each compound was identified. All of the halomalates and both diastereomers of aminomalate underwent oxidative decarboxylation; both diastereomers of 3-thiomalate underwent net nonoxidative decarboxylation. The results were interpreted in terms of a model in which decarboxylation is conformationally controlled. The data are not consistent with a model which suggests that substrates assume the conformation that is necessary to avoid steric crowding between the enzyme and the substituent at the 3-position of the substrate. These data are consistent with a model in which the course of the reaction with (+)-tartrate and meso-tartrate is dictated by the coordination of the substrate hydroxyls to the active site Mn2+. However, the observed reactivities of the 3-methyltartrate diastereomers are not consistent with this model, either: (2R,3R)-3-methyltartrate undergoes oxidative decarboxylation, and (2R,3S)-3-methyltartrate undergoes simple oxidation. These results suggest that for these compounds the conformation is dictated by the positioning of the hydrophobic substituent in a specific binding pocket.(ABSTRACT TRUNCATED AT 250 WORDS)
机译：酒石酸脱氢酶的底物特异性已使用一系列替代底物进行了探索，以鉴定确定特定底物是否进行酶催化脱羧的分子相互作用。制备了一系列3取代的苹果酸类似物，其中F，Cl，Br，I，SH或NH2取代基位于3R-或3S-位置，由酒石酸脱氢酶作用于每个化合物被鉴定。氨基苹果酸的所有卤代酸盐和两种非对映异构体均进行了氧化脱羧。 3-硫代苹果酸的两种非对映异构体均进行了净非氧化脱羧。根据其中构象控制脱羧的模型来解释结果。数据与表明底物采取避免在底物的3-位上的酶和取代基之间的空间拥挤所必需的构象的模型不一致。这些数据与通过底物羟基与活性位点Mn 2+的配位决定与（+）-酒石酸盐和中酒石酸盐的反应过程的模型一致。但是，观察到的3-甲基酒石酸非对映异构体的反应性与该模型不一致，或者：（2R，3R）-3-甲基酒石酸经历了氧化脱羧作用，而（2R，3S）-3-甲基酒石酸酯经历了简单的氧化作用。这些结果表明，对于这些化合物，其构象由疏水取代基在特定结合口袋中的位置决定。（摘要截短为250字）

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