Hiratsuka A, Yokoi A, Sebata N, Watabe T, Satoh K, Hatayama I, Sato K
Department of Hygienic Chemistry, Tokyo College of Pharmacy, Japan.
Biochem Pharmacol. 1989 Aug 15;38(16):2609-13. doi: 10.1016/0006-2952(89)90545-5.
The fluorophotometric substrate, 7-glycidoxycoumarin (GOC), was examined for the assay of epoxide-glutathione (GSH)-conjugating activities of seven major GSH transferases (GSTs) isolated from rat liver cytosols. GST 7-7 (GST-P), isolated from the liver cytosol of rats bearing hepatic hyperplastic nodules, catalysed the GSH conjugation of GOC at a higher rate than any other examined GST isolated from the normal rat liver cytosol. GSTs 3-3, 3-4 and 4-4 (group 3-4 enzymes) had specific activities towards GOC by one fifth to one third of that of GST 7-7. GSTs 1-1, 1-2 and 2-2 (group 1-2 enzymes) had very low activities towards this epoxide. A kinetic study indicated that GST 7-7 showed the largest kappa cat/Km value for the catalytic reaction of GOC-GSH conjugation among the GSTs. In spite of their much smaller kappa cat values, group 3-4 enzymes showed much larger kappa cat/Km values for GOC than the group 1-2 enzymes, because GOC had a much higher affinity for group 3-4 enzymes than for group 1-2 enzymes. A comparative study was also done with GSH conjugations of styrene 7,8-oxide (STO) and 1-chloro-2,4-dinitrobenzene by the GSTs. Unlike GOC, the conjugation of STO was mediated at rates about twice as high by group 3-4 enzymes than by GST 7-7. STO was also a very poor substrate for group 1-2 enzymes.
使用荧光光度法底物7-环氧丙氧基香豆素（GOC），对从大鼠肝脏胞质溶胶中分离出的七种主要谷胱甘肽转移酶（GST）的环氧化物-谷胱甘肽（GSH）结合活性进行测定。从患有肝增生结节的大鼠肝脏胞质溶胶中分离出的GST 7-7（GST-P），催化GOC与GSH结合的速率高于从正常大鼠肝脏胞质溶胶中分离出的任何其他受试GST。GST 3-3、3-4和4-4（3-4组酶）对GOC的比活性是GST 7-7的五分之一到三分之一。GST 1-1、1-2和2-2（1-2组酶）对这种环氧化物的活性非常低。动力学研究表明，在GST中，GST 7-7在GOC-GSH结合的催化反应中显示出最大的催化常数/米氏常数（κcat/Km）值。尽管3-4组酶的催化常数（κcat）值小得多，但它们对GOC的κcat/Km值比1-2组酶大得多，因为GOC对3-4组酶的亲和力比对1-2组酶高得多。还对GST催化的苯乙烯7,8-氧化物（STO）和1-氯-2,4-二硝基苯与GSH的结合进行了比较研究。与GOC不同，STO的结合由3-4组酶介导的速率约为GST 7-7的两倍。STO也是1-2组酶的一种非常差的底物。
