Bauer E, Guo Z, Ueng Y F, Bell L C, Zeldin D, Guengerich F P
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Chem Res Toxicol. 1995 Jan-Feb;8(1):136-42. doi: 10.1021/tx00043a018.
The oxidation of benzo[a]pyrene (B[a]P) was examined using reconstituted systems prepared with recombinant human cytochrome P450 (P450) enzymes 1A1, 1A2, 2C8, 2C10, 2E1, and 3A4 and with microsomes prepared from Saccharomyces cerevisiae expressing recombinant human P450s 2C8, 2C9, and 2C18. Products measured by HPLC included the 3- and 9-phenols, the 4,5-, 7,8-, and 9,10-dihydrodiols (detected in the presence of epoxide hydrolase), and products in the polar fraction eluting immediately after the void volume. The most active enzyme in all reactions was P450 1A1. P450 3A4 and P450 1A2 formed appreciable amounts of several of the products, including the 3-phenol. P450 2C enzymes and P450 2E1 formed relatively low amounts of all B[a]P products. Consideration of these patterns along with knowledge of levels of expression of the P450s in human tissues and previous results with microsomes leads to the conclusion that P450 1A1 should dominate the oxidation of B[a]P in tissues where it is present and inducible. In human liver the level of P450 1A1 is low and P450 3A4, P450 2C subfamily enzymes, and P450 1A2 probably all contribute. Of the human P450s considered here, P450 1A2 was the most active hepatic enzyme forming the 7,8-dihydrodiol. 7,8-Benzoflavone stimulated the oxidation of B[a]P by P450 3A4 and inhibited the oxidations catalyzed by P450 1A2. The extent of inhibition of P450 1A1 was less (than with P450 1A2), probably due to the rapid oxidation of 7,8-benzoflavone by P450 1A1. The major 7,8-benzoflavone product appears to be the 5,6-oxide.
使用由重组人细胞色素P450（P450）酶1A1、1A2、2C8、2C10、2E1和3A4以及由表达重组人P450 2C8、2C9和2C18的酿酒酵母制备的微粒体制备的重组系统，研究了苯并[a]芘（B[a]P）的氧化。通过高效液相色谱法测定的产物包括3-和9-酚、4,5-、7,8-和9,10-二氢二醇（在环氧水解酶存在下检测到）以及在空体积后立即洗脱的极性部分中的产物。所有反应中活性最高的酶是P450 1A1。P450 3A4和P450 1A2形成了相当数量的几种产物，包括3-酚。P450 2C酶和P450 2E1形成的所有B[a]P产物相对较少。结合这些模式以及对人体组织中P450表达水平的了解和先前微粒体实验结果得出结论，在存在且可诱导P450 1A1的组织中，它应主导B[a]P的氧化。在人肝脏中，P450 1A1水平较低，P450 3A4、P450 2C亚家族酶和P450 1A2可能都有贡献。在这里考虑的人P450中，P450 1A2是形成7,8-二氢二醇最活跃的肝脏酶。7,8-苯并黄酮刺激P450 3A4对B[a]P的氧化，并抑制P450 1A2催化的氧化。对P450 1A1的抑制程度较小（比P450 1A2小），可能是由于P450 1A1对7,8-苯并黄酮的快速氧化。7,8-苯并黄酮的主要产物似乎是5,6-氧化物。
