Substrate determinants of the course of tartrate dehydrogenase-catalyzed reactions.
Substrate determinants of the course of tartrate dehydrogenase-catalyzed reactions.
复制标题
酒石酸脱氢酶催化反应过程的底物决定因素。
DOI：
10.1021/bi00022a027
复制
发表时间：
1995
期刊：
影响因子：
2.9
通讯作者：
Tipton,PA
中科院分区：
文献类型：
--
作者：
Serfozo,P;Tipton,PA
Revised Manuscript Received March 27, 1995® abstract: The substrate specificity of tartrate dehydrogenase has been probed using a series of alternative substrates to identify the molecular interactionswhich 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 35-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. Thedata are not consistent with a model which suggests that substrates assume the conformation that is necessary to avoid steric crowding betweenthe 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 me. vo-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:(2/?, 3/?)-3-methyltartrate undergoes oxidative decarboxylation, and (27?, 35)-3-methyltartrate undergoes simpleoxidation. These results suggest that for these compounds the conformation is dictatedby the positioning of the hydrophobic substituent in a specific binding pocket. In fact, the similarity in the Km values for all the (2/?, 35)-3-substituted substrates suggest that they share a common binding mode; the Km\for the (27?, 3/?)-3-substituted substrates are much higher and vary widely, suggesting that they bindin an alternative mode.
