Bertics P J, Edman C F, Karavolas H J
Endocrinology. 1984 Jan;114(1):63-9. doi: 10.1210/endo-114-1-63.
The capacity of the 5 alpha-dihydroprogesterone analog, 4-aza-4-methyl-5 alpha-pregnane-3,20-dione (AMPD), to inhibit progesterone 5 alpha-reductase and both 5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase activities (NADPH- and NADH-linked) from the female rat anterior pituitary has been investigated. Dose response studies demonstrate that AMPD is a powerful inhibitor of pituitary progesterone 5 alpha-reduction but is ineffective at inhibiting either of the 3 alpha-hydroxysteroid oxidoreductase activities, even at concentrations up to 10 microM. A kinetic analysis of the interaction of AMPD with progesterone 5 alpha-reductase indicates that it is a competitive inhibitor vs. progesterone [Kislope = 7.2 +/- 0.6 nM; apparent Michaelis-Menten constant (Km) (progesterone) = 193 +/- 18 nM] and an uncompetitive inhibitor vs. NADPH (Kiintercept = 17.9 +/- 1.4 nM). These inhibition patterns are consistent with the view that NADPH binding precedes that of either AMPD or progesterone. Furthermore, AMPD does not appear to be an irreversible inhibitor since preincubation of the enzyme (at 37 C) with AMPD and NADPH, for periods of time up to 60 min, does not lead to a time-dependent loss of activity. The inhibition can also be readily removed by dilution, even after a 60-min preincubation with the inhibitor and NADPH. It is postulated that the selective and potent inhibition of the 5 alpha-reduction of progesterone by AMPD may be due to the steroid functioning as a transition state analog. This inhibitor should prove useful in studying the properties of progesterone 5 alpha-reductase and the function of anterior pituitary progestin metabolism.
对5α-二氢孕酮类似物4-氮杂-4-甲基-5α-孕烷-3,20-二酮（AMPD）抑制雌性大鼠垂体前叶孕酮5α-还原酶以及5α-二氢孕酮3α-羟基类固醇氧化还原酶两种活性（与NADPH和NADH相关）的能力进行了研究。剂量反应研究表明，AMPD是垂体孕酮5α-还原的强效抑制剂，但即使在浓度高达10μM时，对3α-羟基类固醇氧化还原酶的任何一种活性都无抑制作用。对AMPD与孕酮5α-还原酶相互作用的动力学分析表明，它对孕酮是竞争性抑制剂[Kislope = 7.2±0.6 nM；表观米氏常数（Km）（孕酮） = 193±18 nM]，对NADPH是非竞争性抑制剂（Kiintercept = 17.9±1.4 nM）。这些抑制模式与NADPH结合先于AMPD或孕酮结合的观点一致。此外，AMPD似乎不是不可逆抑制剂，因为在37℃下将酶与AMPD和NADPH预孵育长达60分钟，不会导致活性随时间丧失。即使在与抑制剂和NADPH预孵育60分钟后，通过稀释也能很容易地消除抑制作用。据推测，AMPD对孕酮5α-还原的选择性和强效抑制可能是由于该类固醇作为过渡态类似物发挥作用。这种抑制剂在研究孕酮5α-还原酶的特性和垂体前叶孕激素代谢的功能方面应会很有用。
