Lubet R A, Syi J L, Nelson J O, Nims R W
Laboratory of Comparative Carcinogenesis, National Cancer Institute, Frederick, MD.
Chem Biol Interact. 1990;75(3):325-39. doi: 10.1016/0009-2797(90)90075-x.
The induction of cytochrome P-450-mediated alkoxyresorufin O-dealkylase activities by various xenobiotics was examined in liver from a variety of animal species in order to gain insights into the substrate specificities of the induced P-450s. We found that forms of cytochrome P-450 capable of mediating the O-dealkylation of the short-chain phenoxazone ethers methoxy-, ethoxy- and propoxyresorufin were highly induced by 3-methylcholanthrene-type inducers and by Aroclor-1254 in all species tested, although there were species differences in the relative turnover rates for the various substrates. For example, in hamster liver the turnover rates for the short-chain resorufin ethers decreased in the following order: methoxy greater than ethoxy much greater than propoxy, while in the rat liver almost the exact opposite order was observed: ethoxy = propoxy much greater than methoxy. In contrast, the degree of induction by phenobarbital-type inducers of isozymes catalyzing the O-dealkylation of pentoxy- or benzyloxyresorufin was highly species-dependent. Thus, F344/NCr rats, B6C3F1 mice and NZB rabbits showed the greatest (greater than 20-fold) induction of these activities, either by phenobarbital or Aroclor-1254, while Mongolian gerbils showed intermediate levels of induction and Syrian golden hamsters exhibited very low induction. In the Japanese quail, phenobarbital- or DDT-treatment resulted in minimal induction of pentoxy- or benzyloxyresorufin O-dealkylase activity, although significant induction of the latter activity occurred following treatment with 5,6-benzoflavone or with Aroclor-1254. Since substrate specificities of most enzymes can be rationalized based upon differences in the steric requirements at the enzyme active site, we employed molecular modeling techniques to calculate the molecular dimensions of the alkoxyresorufins. Surprisingly, the minimal energy conformations in vacuo of each of the resorufin ethers examined are essentially planar. However, alternative configurations, especially for the pentoxy- and benxyloxy-ethers, having greater three-dimensional bulk are also energetically possible.
为深入了解诱导型细胞色素P-450的底物特异性，研究了多种外源性物质对不同动物物种肝脏中细胞色素P-450介导的烷氧基试卤灵O-脱烷基酶活性的诱导作用。我们发现，能够介导短链吩恶嗪醚甲氧基、乙氧基和丙氧基试卤灵O-脱烷基作用的细胞色素P-450形式，在所有受试物种中均被3-甲基胆蒽型诱导剂和多氯联苯混合物Aroclor-1254高度诱导，尽管不同底物的相对周转率存在物种差异。例如，在仓鼠肝脏中，短链试卤灵醚的周转率按以下顺序降低：甲氧基＞乙氧基＞＞丙氧基，而在大鼠肝脏中观察到几乎完全相反的顺序：乙氧基 = 丙氧基＞＞甲氧基。相比之下，苯巴比妥型诱导剂对催化戊氧基或苄氧基试卤灵O-脱烷基作用的同工酶的诱导程度高度依赖物种。因此，F344/NCr大鼠、B6C3F1小鼠和NZB兔对这些活性表现出最大程度（＞20倍）的诱导，无论是苯巴比妥还是Aroclor-1254诱导，而蒙古沙鼠表现出中等水平的诱导，叙利亚金黄仓鼠表现出极低的诱导。在日本鹌鹑中，苯巴比妥或滴滴涕处理导致戊氧基或苄氧基试卤灵O-脱烷基酶活性的诱导作用最小，尽管用5,6-苯并黄酮或Aroclor-1254处理后，后者活性有显著诱导。由于大多数酶的底物特异性可根据酶活性位点空间需求的差异进行合理化解释，我们采用分子建模技术计算烷氧基试卤灵的分子尺寸。令人惊讶的是，所研究的每种试卤灵醚在真空中的最低能量构象基本为平面结构。然而，具有更大三维体积的替代构型，特别是对于戊氧基和苄氧基醚，在能量上也是可能的。
