Neal G E, Nielsch U, Judah D J, Hulbert P B
Toxicology Unit, M.R.C. Laboratories, Carshalton, Surrey, U.K.
Biochem Pharmacol. 1987 Dec 15;36(24):4269-76. doi: 10.1016/0006-2952(87)90669-1.
Glutathione-S-transferase (GST) activity has been examined in liver cytosol fractions from guinea pigs, mice, control fed rats or rats with pre-neoplastic nodular liver lesions. The levels of activity in unfractionated cytosols have been assayed using the model substrates 1-chloro-2,4-dinitrobenzene (CDNB), 3,4-dichloronitrobenzene (DCNB) and monobromobimane (mBrB) with reduced glutathione (GSH). The order of activities in the various liver fractions using CDNB as substrate were: mouse greater than pre-neoplastic nodular rat greater than guinea pig greater than control rat and paralleled the capacities of the cytosols to catalyse the formation of aflatoxin B1-GSH from microsomally-activated aflatoxin B1 (AFB1) and GSH. Quantitative differences between the activities of the cytosols using the three model substrates were observed. In the mouse fractionation of GST activity by isoelectric focusing (I.E.F.) on preparative granular gels showed that the most basic component (isoelectric point pH 9.4) with the highest conjugating activity with respect to microsomally-activated AFB1 did not correspond with the peak of most activity for conjugating CDNB. In the pre-neoplastic nodular rat liver the CDNB conjugating activities of all fractions separated on granular I.E.F. gels, were higher than the corresponding fractions isolated from control rat liver, with particular enhancement of the peak containing the 3:3 isoenzyme. In contrast to control rat liver the 7:7 isoenzyme was detected in pre-neoplastic nodular liver preparations. These isoenzymes (3:3 and 7:7) did not contribute significantly to the enhanced level of AFB1-GSH formation catalysed by cytosol fractions prepared from pre-neoplastic nodular rat liver. The microsomally-activated AFB1-conjugating activity of unfractionated rat liver cytosols was increased to a relatively greater extent than CDNB conjugating activity during the induction of pre-neoplastic nodular liver lesions, and the elevated level of the activated AFB1-conjugating activity was found to be associated with the most basic fraction (isoelectric point pH 9.0). Analytical isoelectric focusing gels using mBrB as substrate demonstrated the presence of a basic GST isoenzyme in the pre-neoplastic nodular rat liver, not detected in preparations from the livers of control rats. The low level of activated AFB1-conjugating activity present in unfractionated guinea-pig cytosol was found to correspond with the fraction containing the peak of CDNB conjugating activity on preparative isoelectric focusing (isoelectric point pH 7.5). The lack of correlation between the conjugation of model substrates and the conjugation of xenobiotics could be of import
已对豚鼠、小鼠、对照喂养大鼠或患有癌前结节性肝损伤大鼠的肝细胞溶胶部分中的谷胱甘肽 - S - 转移酶（GST）活性进行了检测。使用模型底物1 - 氯 - 2,4 - 二硝基苯（CDNB）、3,4 - 二氯硝基苯（DCNB）和单溴双马来酰胺（mBrB）与还原型谷胱甘肽（GSH）测定了未分级细胞溶胶中的活性水平。以CDNB为底物时，各种肝脏部分的活性顺序为：小鼠＞癌前结节性大鼠＞豚鼠＞对照大鼠，并且与细胞溶胶催化微粒体激活的黄曲霉毒素B1（AFB1）和GSH形成黄曲霉毒素B1 - GSH的能力平行。观察到使用三种模型底物时细胞溶胶活性之间的定量差异。在小鼠中，通过在制备性颗粒凝胶上进行等电聚焦（I.E.F.）对GST活性进行分级分离表明，相对于微粒体激活的AFB1具有最高共轭活性的最碱性组分（等电点pH 9.4）与共轭CDNB的最大活性峰不对应。在癌前结节性大鼠肝脏中，在颗粒I.E.F.凝胶上分离的所有部分的CDNB共轭活性均高于从对照大鼠肝脏分离的相应部分，含有3:3同工酶的峰有特别增强。与对照大鼠肝脏相反，在癌前结节性肝脏制剂中检测到7:7同工酶。这些同工酶（3:3和7:7）对癌前结节性大鼠肝脏制备的细胞溶胶部分催化的AFB1 - GSH形成增强水平没有显著贡献。在癌前结节性肝损伤诱导过程中，未分级大鼠肝脏细胞溶胶的微粒体激活的AFB1共轭活性比CDNB共轭活性增加的程度相对更大，并且发现激活的AFB1共轭活性的升高水平与最碱性部分（等电点pH 9.0）相关。使用mBrB作为底物的分析性等电聚焦凝胶证明在癌前结节性大鼠肝脏中存在一种碱性GST同工酶，而在对照大鼠肝脏的制剂中未检测到。未分级豚鼠细胞溶胶中存在的低水平激活的AFB1共轭活性被发现与制备性等电聚焦（等电点pH 7.5）上含有CDNB共轭活性峰的部分相对应。模型底物的共轭与异源生物的共轭之间缺乏相关性可能具有重要意义
