Numazawa M, Mutsumi A, Hoshi K, Kigawa H, Oshibe M
Tohoku College of Pharmacy, Sendai, Japan.
J Steroid Biochem Mol Biol. 1991 Dec;39(6):959-66. doi: 10.1016/0960-0760(91)90356-a.
19-Hydroxyandrost-4-ene-3,6,17-trione (19-OHAT), its 19-oxo derivative (19-oxo AT) and 4 beta, 5 beta-epoxyandrostane-3,6,17-trione (5) were synthesized as possible intermediates involved in a mechanism-based inactivation of aromatase caused by androst-4-ene-3,6,17-trione (AT). These compounds, inhibited the enzyme in a competitive manner with Ki's of 0.61, 7.5 and 5.1 microM for 19-OHAT, 19-oxo AT, and compound 5. The two 19-oxygenated steroids showed a time-dependent, pseudo-first order rate of inactivation of aromatase with kinact's of 0.222 and 0.076 min-1 for 19-OHAT and 19-oxo AT, respectively, while compound 5 did not. NADPH and oxygen were required for the inactivation. Androstenedione blocked the inactivation, while L-cysteine partially prevented that of 19-OHAT and almost completely that of 19-oxo AT. When the 19-oxygenated steroids were separately subjected to reaction with N-acetyl-L-cysteine, these rapidly disappeared from the reaction mixture with t1/2 of 25 min (19-OHAT) and 20 s (19-oxo AT). This finding indicates that L-cysteine prevents inactivation by a chemical dependent elimination of the inhibitors from the incubate. These results suggest that the 19-oxygenation rather than the 4,5-epoxidation may be involved in the time-dependent inactivation by AT.
合成了19-羟基雄甾-4-烯-3,6,17-三酮（19-OHAT）、其19-氧代衍生物（19-氧代AT）和4β,5β-环氧雄甾烷-3,6,17-三酮（5），它们可能是雄甾-4-烯-3,6,17-三酮（AT）引起的基于机制的芳香化酶失活过程中的中间体。这些化合物对该酶具有竞争性抑制作用，19-OHAT、19-氧代AT和化合物5的抑制常数（Ki）分别为0.61、7.5和5.1微摩尔。这两种19-氧化甾体对芳香化酶表现出时间依赖性的假一级失活速率，19-OHAT和19-氧代AT的失活速率常数（kinact）分别为0.222和0.076分钟-1，而化合物5则没有。失活过程需要烟酰胺腺嘌呤二核苷酸磷酸（NADPH）和氧气。雄烯二酮可阻断失活，而L-半胱氨酸可部分阻止19-OHAT的失活，并几乎完全阻止19-氧代AT的失活。当19-氧化甾体分别与N-乙酰-L-半胱氨酸反应时，它们在反应混合物中迅速消失，19-OHAT的半衰期（t1/2）为25分钟，19-氧代AT的t1/2为20秒。这一发现表明，L-半胱氨酸通过化学依赖性地从孵育物中消除抑制剂来阻止失活。这些结果表明，AT引起的时间依赖性失活可能涉及19-氧化而非4,5-环氧化。
