Conversion of 19-oxo[2 beta-2H]androgens into oestrogens by human placental aromatase. An unexpected stereochemical outcome.
Conversion of 19-oxo[2 beta-2H]androgens into oestrogens by human placental aromatase. An unexpected stereochemical outcome.
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人胎盘芳香酶将 19-氧代[2β-2H]雄激素转化为雌激素。
DOI：
10.1042/bj2680553
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
Robinson,CH
中科院分区：
文献类型：
--
作者：
Cole,PA;Robinson,CH
芳香酶是一种细胞色素P-450酶，通过19-甲基的连续氧化催化雄激素转化为雌激素。尽管深入研究，第三步的机制，19-醛转化为雌激素，仍然没有解决。我们以前已经发现，一个预烯醇化的19-铝衍生物进行顺利的芳构化在非酶模型研究，但烯醇化的作用，由酶在19-oxoandrogens的转化以前没有被调查。现在已经合成了化合物19-氧代[2 β-2H]睾酮和19-氧代[2 β-2H]雄烯二酮。在不存在NADPH的情况下，将这些化合物暴露于微粒体芳香化酶中，长时间不会导致C-2处的2 H损失或差向异构化，因此活性位点碱基的重要性尚未确定。然而，在NADPH存在下，在19-氧代[2 β-2H]-睾酮与19-氧代[2 β-2H]雄烯二酮的酶诱导芳构化中，C-2处H损失的立体选择性存在意外的底物依赖性差异。17 β-醇衍生物19-氧代[2 β-2H]-睾酮的芳构化结果对应于从未标记的19-氧代睾酮损失约1.2 ∶ 1的2 β-H/2 α-H。相反，19-氧代[2 β-2H]雄烯二酮的芳构化结果对应于未标记的19-氧代雄烯二酮的至少11：1的2 β-H/2 α-H损失。这种底物依赖性的立体选择性意味着在2-H去除酶活性位点的基地的直接作用。此外，这些结果反驳了2 β-羟基化是芳香酶作用中强制性的第三步的提议。
Aromatase is a cytochrome P-450 enzyme that catalyzes the conversion of androgens into oestrogens via sequential oxidations at the 19-methyl group. Despite intensive investigation, the mechanism of the third step, conversion of the 19-aldehydes into oestrogens, has remained unsolved. We have previously found that a pre-enolized 19-al derivative undergoes smooth aromatization in non-enzymic model studies, but the role of enolization by the enzyme in transformations of 19-oxoandrogens has not been previously investigated. The compounds 19-oxo[2 beta-2H]testosterone and 19-oxo[2 beta-2H]androstenedione have now been synthesized. Exposure of either of these compounds to microsomal aromatase, in the absence of NADPH, for an extended period led to no significant 2H loss or epimerization at C-2, leaving open the importance of an active-site base. However, in the presence of NADPH there was an unexpected substrate-dependent difference in the stereoselectivity of H loss at C-2 in the enzyme-induced aromatization of 19-oxo[2 beta-2H]-testosterone versus 19-oxo[2 beta-2H]androstenedione. The aromatization results for 17 beta-ol derivative 19-oxo[2 beta-2H]-testosterone correspond to about 1.2:1 2 beta-H/2 alpha-H loss from unlabelled 19-oxotestosterone. In contrast, aromatization results for 19-oxo[2 beta-2H]androstenedione correspond to at least 11:1 2 beta-H/2 alpha-H loss from unlabelled 19-oxoandrostenedione. This substrate-dependent stereoselectivity implies a direct role for an enzyme active-site base in 2-H removal. Furthermore, these results argue against the proposal that 2 beta-hydroxylation is the obligatory third step in aromatase action.