Boehlert C C, Armstrong R N
Biochem Biophys Res Commun. 1984 Jun 29;121(3):980-6. doi: 10.1016/0006-291x(84)90773-3.
The stereoselectivity of the closely related isozymes A2 and C2 of rat liver glutathione S-transferase toward several arene and azaarene oxides is examined. Isozyme C2 is stereospecific, catalyzing attack of glutathione at the oxirane carbon of R absolute configuration for a series of K-region arene oxides including phenanthrene 9,10-oxide, 1. Substitution of nitrogen in the biphenyl system of 1 causes a loss in stereospecificity. Isozyme A2 exhibits a low degree of stereoselectivity toward both arene and azaarene oxides. Kinetic studies of the two isozymes show that although isozyme C2 turns over 1 faster than does isozyme A2 the opposite is true when 4,5- diazaphenanthrene 9,10-oxide is the substrate. The kinetic and stereochemical behavior of the homodimeric isozymes A2 and C2 can be used to predict the stereoselectivity of the heterodimeric isozyme AC perhaps suggesting that catalysis is insensitive to different subunit-subunit interactions in the three isozymes.
对大鼠肝脏谷胱甘肽S-转移酶密切相关的同工酶A2和C2对几种芳烃和氮杂芳烃氧化物的立体选择性进行了研究。同工酶C2具有立体特异性，对于一系列K区域芳烃氧化物（包括菲9,10-氧化物1），它催化谷胱甘肽在具有R绝对构型的环氧乙烷碳上发生反应。在1的联苯系统中用氮取代会导致立体特异性丧失。同工酶A2对芳烃和氮杂芳烃氧化物均表现出较低程度的立体选择性。对这两种同工酶的动力学研究表明，虽然同工酶C2催化1的周转速度比同工酶A2快，但当以4,5-二氮杂菲9,10-氧化物为底物时情况则相反。同二聚体同工酶A2和C2的动力学和立体化学行为可用于预测异二聚体同工酶AC的立体选择性，这或许表明催化作用对三种同工酶中不同的亚基-亚基相互作用不敏感。
