Morton D J, Forbes H J
Department of Pharmacy, University of Zimbabwe, Harare.
J Pineal Res. 1989;6(3):259-65. doi: 10.1111/j.1600-079x.1989.tb00422.x.
The effect of pteridines and sex hormones on hydroxyindole-O-methyltransferase (HIOMT) catalysis was examined. Equivalent quantities of partially purified bovine HIOMT was incubated in the presence and absence of the various test substances and the results fitted to the Michaelis-Menten equation. The pteridines (triampterene and xanthopterin) had no noticeable effect on HIOMT catalysis, while all the sex hormones examined were found to be competitive inhibitors of the enzyme with respect to the hydroxy-substrate. Testosterone concentrations causing noticeable inhibition were above physiological while estrone, estradiol, and progesterone all caused inhibition within the physiological range; estrone was the most potent and progesterone the least potent inhibitor. The possible significance of these findings are discussed.
研究了蝶啶和性激素对羟基吲哚 - O - 甲基转移酶（HIOMT）催化作用的影响。将等量的部分纯化牛HIOMT在有和没有各种测试物质的情况下进行孵育，结果符合米氏方程。蝶啶（三氨蝶呤和黄蝶呤）对HIOMT催化作用没有明显影响，而所有检测的性激素被发现是该酶针对羟基底物的竞争性抑制剂。引起明显抑制的睾酮浓度高于生理水平，而雌酮、雌二醇和孕酮在生理范围内均引起抑制作用；雌酮是最有效的抑制剂，孕酮是最无效的抑制剂。讨论了这些发现的可能意义。
