Ramsdell H S, Eaton D L
Department of Environmental Health, University of Washington, Seattle 98195.
Toxicol Appl Pharmacol. 1990 Sep 1;105(2):216-25. doi: 10.1016/0041-008x(90)90183-u.
As part of the studies of the biochemical basis for species differences in biotransformation of the carcinogen aflatoxin B1 (AFB1) and its modulation by phenolic antioxidants, we have investigated the role of mouse liver glutathione S-transferase (GST) isoenzymes in the conjugation of AFB1-8,9-epoxide. Isoenzymes of GST were purified to electrophoretic homogeneity from Swiss-Webster mouse liver cytosol by affinity chromatography and chromatofocusing. The isoenzyme fractions were characterized in terms of activity toward surrogate substrates and immunologic cross-reactivity with antisera to rat GSTs. The major isoenzymes were identified as SW 4-4, SW 3-3, and SW 1-1. The specific activity of SW 4-4 toward AFB1-8,9-epoxide was at least 50- and 150-fold greater than that of SW 3-3 and SW 1-1, respectively. Relatively high activity toward another epoxide carcinogen, benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide, was observed with both SW 4-4 and SW 3-3. SW 1-1 had the highest activity toward 1-chloro-2,4-dinitrobenzene (CDNB) whereas SW 4-4 had relatively low CDNB activity. Following pretreatment with 0.75% butylated hydroxyanisole in the diet, the fraction of total GST contributed by SW 1-1 appeared to increase dramatically, whereas in control mice SW 3-3 constituted the predominant isoenzyme. The high GST activity of mouse liver cytosol toward AFB1-8,9-epoxide is apparently due to an isoenzyme that contributes little to the overall cytosolic CDNB activity.
作为对致癌物黄曲霉毒素B1（AFB1）生物转化中物种差异及其受酚类抗氧化剂调节的生化基础研究的一部分，我们研究了小鼠肝脏谷胱甘肽S-转移酶（GST）同工酶在AFB1-8,9-环氧化物结合中的作用。通过亲和色谱和色谱聚焦从瑞士-韦伯斯特小鼠肝脏胞质溶胶中纯化GST同工酶至电泳纯。根据对替代底物的活性以及与大鼠GST抗血清的免疫交叉反应性对同工酶组分进行表征。主要的同工酶被鉴定为SW 4-4、SW 3-3和SW 1-1。SW 4-4对AFB1-8,9-环氧化物的比活性分别比SW 3-3和SW 1-1高至少50倍和150倍。SW 4-4和SW 3-3对另一种环氧化物致癌物苯并[a]芘-7,8-二氢二醇-9,10-环氧化物均表现出相对较高的活性。SW 1-1对1-氯-2,4-二硝基苯（CDNB）的活性最高，而SW 4-4的CDNB活性相对较低。在饮食中用0.75%的丁基化羟基茴香醚预处理后，SW 1-1在总GST中所占的比例似乎急剧增加，而在对照小鼠中SW 3-3是主要的同工酶。小鼠肝脏胞质溶胶对AFB1-8,9-环氧化物的高GST活性显然归因于一种对总体胞质CDNB活性贡献不大的同工酶。
