FINASTERIDE - A SLOW-BINDING 5-ALPHA-REDUCTASE INHIBITOR
FINASTERIDE - A SLOW-BINDING 5-ALPHA-REDUCTASE INHIBITOR
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DOI：
10.1021/bi00072a028
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发表时间：
1993-06-01
期刊：
影响因子：
2.9
通讯作者：
NICK, H
中科院分区：
文献类型：
--
作者：
FALLER, B;FARLEY, D;NICK, H
用人前列腺组织的微粒体制剂研究了类固醇5α-还原酶与已知的5α-还原酶抑制剂非那雄胺的相互作用动力学。据报道，该分子以竞争性的方式可逆地与睾酮结合，K(I)值在10 NM范围内。本文提出的结果表明，酶-抑制物复合体的形成并不像以前的研究假设的那样是瞬时发生的。在中性pH和37℃条件下，酶与缓蚀剂的结合符合速率常数k(On)=2.7×10~(5)M~(-1)·S~(-1)。较低的k(ON)值与较高的缔合反应活化能(150kJ·mol~(-1))相结合，表明缔合过程不受扩散控制，可能通过中间步骤进行。然而，在所研究的缓蚀剂浓度下，没有动力学地检测到这样的中间体。因此，我们得出结论，酶与抑制剂初始结合的平衡解离常数K(I)*大于1.5×10~(-7)M，即使在低至1 nM的抑制剂浓度下，反应也完全转移到EI络合物中，一旦达到平衡，就没有检测到残留的活性。因此，非那雄胺与5α-还原酶的相互作用也可以用很低的总平衡解离常数(K(I))来表征。
A microsomal preparation of human prostatic tissue was used to study the kinetics of interaction of steroid 5alpha-reductase with finasteride, a known 5alpha-reductase inhibitor. This molecule has been reported to reversibly bind 5alpha-reductase in a competitive manner to testosterone with a K(i) value in the 10 nM range. The results presented in this paper show that enzyme-inhibitor complex formation does not take place instantaneously as assumed in previous studies. At neutral pH and 37-degrees-C, the association of enzyme with inhibitor is governed by a rate constant, k(on), of 2.7 X 10(5) M-1 s-1. This low k(on) value, in combination with the high energy of activation of the association reaction (150 kJ mol-1), indicates that the association process is not diffusion controlled and may proceed through intermediate steps. However, such an intermediate was not detected kinetically under the inhibitor concentrations investigated. We therefore conclude that the equilibrium dissociation constant, K(i)*, for the initial binding of the enzyme to the inhibitor is higher than 1.5 X 10(-7) M. Even at inhibitor concentrations as low as 1 nM, the reaction was completely displaced to the EI complex and no residual activity detected once the equilibrium was reached. Hence, the interaction between finasteride and 5alpha-reductase can also be characterized by a very low overall equilibrium dissociation constant (K(i)