Evaluation of atypical cytochrome P450 kinetics with two-substrate models: Evidence that multiple substrates can simultaneously bind to cytochrome P450 active sites
Evaluation of atypical cytochrome P450 kinetics with two-substrate models: Evidence that multiple substrates can simultaneously bind to cytochrome P450 active sites
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DOI：
10.1021/bi9715627
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发表时间：
1998-03-24
期刊：
影响因子：
2.9
通讯作者：
Tracy, TS
中科院分区：
文献类型：
--
作者：
Korzekwa, KR;Krishnamachary, N;Tracy, TS
一些细胞色素P450催化的反应表现出非典型的动力学过程，这些动力学过程可分为五类：激活、自激活、部分抑制、底物抑制和两相饱和曲线。提出了一个双位点模型，在该模型中酶可以同时结合两个底物分子，该模型可以用来描述所有这些观察到的动力学性质。细胞色素P450 3A4代谢卡马西平，细胞色素P450 2B6、2C8、2C9和3A5代谢萘，细胞色素P450 2C9代谢氨苯砜，符合S型动力学特征。CYP3A4代谢萘和CYP2C9代谢萘普生符合非双曲线动力学规律，第一底物分子具有低K-m、低V-max组分，第二底物分子具有高K-m、高V-max组分。7，8-苯并黄酮对细胞色素P3A4对菲代谢的激活作用，氨苯砜对氟比洛芬和萘普生代谢的激活作用。此外，还观察到菲对7，8-苯并黄酮代谢的部分抑制作用，这些结果表明，不同的P450亚型可能表现出非典型的酶动力学，这取决于所使用的底物(S)，这些结果可以用一个包括活性部位两个底物分子同时结合的模型来解释。
Some cytochrome P450 catalyzed reactions show atypical kinetics, and these kinetic processes can be grouped into five categories: activation, autoactivation, partial inhibition, substrate inhibition, and biphasic saturation curves. A two-site model in which the enzyme can bind two substrate molecules simultaneously is presented which can be used to describe all of these observed kinetic properties. Sigmoidal kinetic characteristics were observed for carbamazepine metabolism by CYP3A4 and naphthalene metabolism by CYPs 2B6, 2C8, 2C9, and 3A5 as well as dapsone metabolism by CYP2C9. Naphthalene metabolism by CYP3A4 and naproxen metabolism by CYP2C9 demonstrated nonhyperbolic enzyme kinetics suggestive of a low K-m, low V-max component for the first substrate molecule and a high K-m, high V-max component for the second substrate molecule. 7,8-Benzoflavone activation of phenanthrene metabolism by CYP3A4 and dapsone activation of flurbiprofen and naproxen metabolism by CYP2C9 were also observed. Furthermore, partial inhibition of 7,8-benzoflavone metabolism by phenanthrene was observed, These results demonstrate that various P450 isoforms may exhibit atypical enzyme kinetics depending on the substrate(s) employed and that these results may be explained by a model which includes simultaneous binding of two substrate molecules in the active site.