Effects of 8-methoxypsoralen on cytochrome P450 2A13
Effects of 8-methoxypsoralen on cytochrome P450 2A13
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DOI：
10.1093/carcin/bgh348
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发表时间：
2005-03-01
期刊：
影响因子：
4.7
通讯作者：
Hollenberg, PF
中科院分区：
文献类型：
--
作者：
von Weymarn, LB;Zhang, QY;Hollenberg, PF
细胞色素P450 2A 13在体外有效催化几种烟草特有亚硝胺的生物活化。这种有效的生物激活与P450 2A 13在人肺中的选择性表达一起表明，这种P450可能在吸烟者肺癌的发生中起重要作用。因此，鉴定P450 2A 13的有效和选择性抑制剂/灭活剂可能有助于降低吸烟者患肺癌的风险。在这项研究中，我们研究了8-甲氧基补骨脂素（8-MOP），一种已知的P450 2A 6抑制剂，抑制和破坏异源表达的P450 2A 13在重组系统中的活性的能力。我们发现，8-MOP是P450 2A 13介导的几种化合物代谢的有效抑制剂，包括睾酮，这是未知的P450 2A 13底物。8-MOP对P450 2A 13介导的香豆素7-羟基化的非竞争性抑制的K-I为0.11 μ M。P450 2A 13的抑制伴随着酶的失活。因此，观察到的活性降低很可能是由于酶的失活以及8-MOP对P450 2A 13的竞争性或非竞争性抑制。失活没有导致天然血红素的损失，或P450的还原CO谱的显著变化，并且没有产生任何可检测的血红素加合物。相反，8-MOP通过与脱辅基蛋白形成加合物使P450 2A 13失活。加合蛋白的LC/MS分析表明，与未加合蛋白相比，质量增加了232 Da。该质量偏移与向P450脱辅基蛋白添加一个分子的8-MOP加上一个氧原子有关。
Cytochrome P450 2A13 efficiently catalyzes the bioactivation of several tobacco-specific nitrosamines in vitro. This efficient bioactivation together with the selective expression of P450 2A13 in the human lung suggests that this P450 may play an important role in the initiation of lung cancer in smokers. Therefore, the identification of potent and selective inhibitors/inactivators of P450 2A13 could potentially help to lower the risk of lung cancer in smokers. In this study, we investigated the ability of 8-methoxypsoralen (8-MOP), a known inhibitor of P450 2A6, to inhibit and inactivate the activities of heterologously expressed P450 2A13 in reconstituted systems. We found that 8-MOP is a potent inhibitor of P450 2A13-mediated metabolism of several compounds, including testosterone, which had not been known to be a P450 2A13 substrate. The K-I for the non-competitive inhibition of P450 2A13-mediated coumarin 7-hydroxylation by 8-MOP was 0.11 muM. The inhibition of P450 2A13 was accompanied by inactivation of the enzyme. Therefore, the observed decrease in activity is most likely due to the inactivation of the enzyme together with competitive or non-competitive inhibition of P450 2A13 by 8-MOP. The inactivation did not result in a loss of native heme, or a significant change in the reduced-CO spectrum of the P450, and did not generate any detectable heme adducts. Instead, the inactivation of P450 2A13 by8-MOP occurred through the formation of an adduct to the apoprotein. LC/MS analysis of the adducted protein indicated an increase in the mass of 232 Da compared with the unadducted protein. This mass shift correlates with the addition of one molecule of 8-MOP plus one atom of oxygen atom to the P450 apoprotein.