Rearrangement of L-2-hydroxyglutarate to L-threo-3-methylmalate catalyzed by adenosylcobalamin-dependent glutamate mutase.
Rearrangement of L-2-hydroxyglutarate to L-threo-3-methylmalate catalyzed by adenosylcobalamin-dependent glutamate mutase.
复制标题
由腺苷钴胺素依赖性谷氨酸变位酶催化 L-2-羟基戊二酸重排为 L-苏型-3-甲基苹果酸。
DOI：
10.1021/bi000121b
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
Marsh,EN
中科院分区：
文献类型：
--
作者：
Roymoulik,I;Moon,N;Dunham,WR;Ballou,DP;Marsh,EN
Adenosylcobalamin-dependent enzymes catalyze a variety of chemically difficult isomerizations in which a nonacidic hydrogen on one carbon is interchanged with an electron-withdrawing group on an adjacent carbon. We describe a new isomerization, that ofl-2-hydroxyglutarate tol-threo-3-methylmalate, involving the migration of the carbinol carbon. This reaction is catalyzed by glutamate mutase, butkcat= 0.05 s-1is much lower than that for the natural substrate,l-glutamate (kcat= 5.6 s-1). EPR spectroscopy confirms that the major organic radical that accumulates on the enzyme is the C-4 radical ofl-2-hydroxyglutarate. Pre-steady-state kinetic measurements revealed thatl-2-hydroxyglutarate-induced homolysis of AdoCbl occurs very rapidly, with a rate constant approaching those measured previously with glutamate and methylaspartate as substrates. These observations are consistent with the rearrangement of the 2-hydroxyglutaryl radical being the rate-determining step in the reaction. The slow rearrangement of the 2-hydroxyglutaryl radical can be attributed to the poor stabilization by the hydroxyl group of the migrating glycolyl moiety of the radical transiently formed on the migrating carbon. In contrast, with the normal substrate the migrating carbon atom bears a nitrogen substituent that better stabilizes the analogous glycyl moiety. These studies point to the importance of the functional groups attached to the migrating carbon in facilitating the carbon skeleton rearrangement.
