Duignan D B, Sipes I G, Ciaccio P J, Halpert J R
Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721.
Arch Biochem Biophys. 1988 Nov 15;267(1):294-304. doi: 10.1016/0003-9861(88)90035-5.
We have investigated the metabolism of polychlorinated biphenyls and endogenous steroids by the major phenobarbital (PB)-inducible hepatic cytochromes P450 in dogs and rats, PBD-2 and PB-B, respectively. Previous results from our laboratory indicate that dog PBD-2 purified from microsomes of PB-treated animals is similar to rat PB-B with respect to structure and the regioselective metabolism of warfarin and androstenedione. The results also strongly suggest that PBD-2 is the P450 form responsible for metabolizing 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB) in liver microsomes from untreated dogs. In the present study, a cytochrome P450 with similar chromatographic behavior to that of PBD-2 has been purified from liver microsomes of untreated dogs. This protein is identical to PBD-2 based on (i) mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (ii) reactivity with anti-PBD-2 IgG, (iii) amino-terminal sequence, and (iv) 245-HCB metabolite profile. Induction and antibody-inhibition data suggest that PBD-2 is responsible for the metabolism of 2,2',3,3',6,6'-hexachlorobiphenyl (236-HCB) in microsomes obtained from both untreated and PB-treated dogs. In contrast, metabolism of 4,4'-dichlorobiphenyl (4-DCB) by dog microsomes is poor, and does not appear to be catalyzed to a significant extent by PBD-2. Antibody-inhibition studies with intact microsomes corroborate previous results that androstenedione is metabolized by purified PBD-2 to the same major metabolite (16 beta-OH androstenedione) produced by rat PB-B. Dog PBD-2 metabolizes progesterone primarily to the 21-OH metabolite, while metabolism by rat PB-B leads to the formation of the 16 alpha-OH product. On the other hand, upon Ouchterlony double-immunodiffusion analysis, anti-PBD-2 IgG reacts strongly with PB-B but not PB-C, the major rat liver progesterone 21-hydroxylase. The data suggest that dog PBD-2 is a constitutive P450 important in the metabolism of various PCBs and endogenous steroids. Dog PBD-2 and rat PB-B appear to be similar enzymes, yet they differ in their regioselective metabolism of progesterone.
我们分别研究了犬和大鼠体内主要的苯巴比妥（PB）诱导型肝细胞色素P450（分别为PBD - 2和PB - B）对多氯联苯和内源性类固醇的代谢情况。我们实验室之前的结果表明，从PB处理动物的微粒体中纯化得到的犬PBD - 2在结构以及对华法林和雄烯二酮的区域选择性代谢方面与大鼠PB - B相似。结果还强烈表明，PBD - 2是未处理犬肝脏微粒体中负责代谢2,2',4,4',5,5'-六氯联苯（245 - HCB）的P450形式。在本研究中，从未处理犬的肝脏微粒体中纯化出了一种色谱行为与PBD - 2相似的细胞色素P450。基于以下几点，该蛋白质与PBD - 2相同：（i）在十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳上的迁移率；（ii）与抗PBD - 2 IgG的反应性；（iii）氨基末端序列；（iv）245 - HCB代谢产物谱。诱导和抗体抑制数据表明，PBD - 2负责未处理和PB处理犬的微粒体中2,2',3,3',6,6'-六氯联苯（236 - HCB）的代谢。相比之下，犬微粒体对4,4'-二氯联苯（4 - DCB）的代谢较差，且似乎在很大程度上不是由PBD - 2催化的。对完整微粒体的抗体抑制研究证实了之前的结果，即雄烯二酮被纯化的PBD - 2代谢为与大鼠PB - B产生的相同主要代谢产物（16β - 羟基雄烯二酮）。犬PBD - 2主要将孕酮代谢为21 - 羟基代谢产物，而大鼠PB - B的代谢则导致形成16α - 羟基产物。另一方面，在双向免疫扩散分析中，抗PBD - 2 IgG与PB - B强烈反应，但与大鼠肝脏主要的孕酮21 - 羟化酶PB - C不反应。数据表明，犬PBD - 2是一种在各种多氯联苯和内源性类固醇代谢中起重要作用的组成型P450。犬PBD - 2和大鼠PB - B似乎是相似的酶，但它们在孕酮的区域选择性代谢方面存在差异。
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