Duignan D B, Sipes I G, Leonard T B, Halpert J R
Arch Biochem Biophys. 1987 Jun;255(2):290-303. doi: 10.1016/0003-9861(87)90396-1.
The biochemical basis for the marked difference in the rate of the hepatic metabolism of 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB) by Beagle dogs and Sprague-Dawley rats has been investigated. Control dog liver microsomes metabolize this substrate 15 times faster than control rat liver microsomes. Upon treatment with phenobarbital (PB), at least two cytochrome P-450 isozymes are induced in the dog, and the hepatic microsomal metabolism of 245-HCB is increased on both a per nanomole P-450 basis (twofold) and a per milligram protein basis (fivefold). One of the PB-induced isozymes, PBD-2, has been purified to a specific content of 17-19 nmol/mg protein and to less than 95% homogeneity, as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In a reconstituted system containing cytochrome b5, this isozyme shows an activity toward 245-HCB which is greater than threefold that seen in intact liver microsomes from PB-induced dogs. A reconstituted system containing the major isozyme induced by PB in the rat (PB-B) metabolizes 245-HCB at 1/10 the rate observed with purified PBD-2. Antibody inhibition studies have shown that PBD-2 accounts for greater than 90% of the hepatic microsomal metabolism of 245-HCB in control and PB-induced dogs, while PB-B only accounts for about half of the metabolism of this compound by microsomes obtained from PB-treated rats. Immunoblot analysis has revealed that the level of PBD-2 in dog liver microsomes increases nearly sixfold with PB treatment, and this increase correlates well with the fivefold increase in the rate of hepatic microsomal metabolism of 245-HCB by dogs. Together these data support a primary role for isozyme PBD-2 in the hepatic metabolism of 245-HCB in control and PB-induced dogs. In addition, these results suggest that, in contrast to rats, dogs can readily metabolize 245-HCB as a result of the presence of a cytochrome P-450 isozyme with efficient 245-HCB metabolizing activity.
研究了比格犬和斯普拉格-道利大鼠对2,2',4,4',5,5'-六氯联苯（245-HCB）肝脏代谢速率存在显著差异的生化基础。对照犬肝脏微粒体代谢该底物的速度比对照大鼠肝脏微粒体快15倍。用苯巴比妥（PB）处理后，犬体内至少诱导出两种细胞色素P-450同工酶，并且245-HCB的肝脏微粒体代谢在每纳摩尔P-450基础上（增加两倍）和每毫克蛋白质基础上（增加五倍）均有所增加。其中一种PB诱导的同工酶PBD-2已被纯化至蛋白质含量为17 - 19 nmol/mg，且通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳证明其纯度低于95%。在含有细胞色素b5的重组系统中，这种同工酶对245-HCB的活性比对PB诱导犬的完整肝脏微粒体中的活性高3倍以上。含有大鼠中由PB诱导的主要同工酶（PB-B）的重组系统代谢245-HCB的速率是纯化的PBD-2的1/10。抗体抑制研究表明，在对照和PB诱导的犬中，PBD-2占肝脏微粒体245-HCB代谢的90%以上，而PB-B仅占PB处理大鼠微粒体对该化合物代谢的约一半。免疫印迹分析显示，犬肝脏微粒体中PBD-2的水平经PB处理后增加近6倍，且这种增加与犬肝脏微粒体对245-HCB代谢速率增加5倍密切相关。这些数据共同支持同工酶PBD-2在对照和PB诱导的犬肝脏245-HCB代谢中起主要作用。此外，这些结果表明，与大鼠不同，由于存在具有高效245-HCB代谢活性的细胞色素P-450同工酶，犬能够轻易代谢245-HCB。
