Hu X, Singh S V
Cancer Research Laboratory, Mercy Cancer Institute, Mercy Hospital of Pittsburgh, Pennsylvania 15219, USA.
Arch Biochem Biophys. 1997 Sep 15;345(2):318-24. doi: 10.1006/abbi.1997.0270.
The kinetics of the conjugation of carcinogenic anti-diol epoxides of chrysene (anti-CDE) and benzo(g)chrysene [anti-B(g)CDE] with glutathione (GSH) catalyzed by GSH S-transferase (GST) isoenzymes mGSTP1-1, mGSTM1-1, mGSTA3-3, mGSTA4-4, and GST 9.5 of female A/J mouse tissues has been investigated. When GST activity was measured as a function of varying anti-CDE or anti-B(g)-CDE concentrations at a fixed concentration of GSH, each isoenzyme obeyed Michaelis-Menten kinetics. The catalytic efficiencies (k(cat)/Km) of murine GSTs in the GSH conjugation of anti-CDE were in the order of GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3 > mGSTA4-4. While each GST isoenzyme examined in the present study exhibited preference for the GSH conjugation of (+)-anti-CDE with the (R,S)-diol (S,R)-epoxide absolute configuration, which is a far more potent carcinogen than the (-)-anti-CDE [(S,R)-diol (R,S)-epoxide absolute configuration], the enantioselectivity was relatively more pronounced for mGSTP1-1 compared with other murine GSTs. Anti-B(g)CDE was a relatively poor substrate for each GST isoenzyme examined compared with anti-CDE. The catalytic efficiencies of murine GSTs in the GSH conjugation of anti-B(g)CDE were in the order of GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3. With the exception of mGSTM1-1, all other murine GSTs exhibited preference for the GSH conjugation of anti-B(g)CDE enantiomer with the (R,S)-diol (S,R)-epoxide absolute configuration. In summary, the results of the present study indicate that the murine GSTs significantly differ in their catalytic efficiency and enantioselectivity in the GSH conjugation of both anti-CDE and anti-B(g)CDE, and that anti-B(g)CDE is a relatively poor substrate for murine GSTs compared with anti-CDE, which may partially account for the observed relatively higher carcinogenic potency of the former compound.
研究了雌性A/J小鼠组织中的谷胱甘肽S-转移酶（GST）同工酶mGSTP1-1、mGSTM1-1、mGSTA3-3、mGSTA4-4和GST 9.5催化的致癌性苯并[a]芘反式二醇环氧化物（反式-CDE）和苯并[g]芘[反式-B(g)CDE]与谷胱甘肽（GSH）的结合动力学。当在固定GSH浓度下测量GST活性作为反式-CDE或反式-B(g)-CDE浓度变化的函数时，每种同工酶均遵循米氏动力学。小鼠GST在反式-CDE的GSH结合中的催化效率（k(cat)/Km）顺序为GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3 > mGSTA4-4。虽然本研究中检测的每种GST同工酶都表现出对具有（R,S）-二醇（S,R）-环氧化物绝对构型的（+）-反式-CDE的GSH结合的偏好，（+）-反式-CDE是比（-）-反式-CDE[（S,R）-二醇（R,S）-环氧化物绝对构型]更强的致癌物，但与其他小鼠GST相比，mGSTP1-1的对映选择性相对更明显。与反式-CDE相比，反式-B(g)CDE是所检测的每种GST同工酶的相对较差的底物。小鼠GST在反式-B(g)CDE的GSH结合中的催化效率顺序为GST 9.5 > mGSTP1-1 > mGSTM1-1 > mGSTA3-3。除mGSTM1-1外，所有其他小鼠GST均表现出对具有（R,S）-二醇（S,R）-环氧化物绝对构型的反式-B(g)CDE对映体的GSH结合的偏好。总之，本研究结果表明，小鼠GST在反式-CDE和反式-B(g)CDE的GSH结合中的催化效率和对映选择性存在显著差异，并且与反式-CDE相比，反式-B(g)CDE是小鼠GST的相对较差的底物，这可能部分解释了观察到的前一种化合物相对较高的致癌潜力。
