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胆固醇氧化酶的3-氧代甾体δ4-δ5-异构酶组分的底物特异性、立体化学、可逆性及抑制作用

The substrate specificity and stereochemistry, reversibility and inhibition of the 3-oxo steroid delta 4-delta 5-isomerase component of cholesterol oxidase.

作者信息

Smith A G, Brooks C J

出版信息

Biochem J. 1977 Oct 1;167(1):121-9. doi: 10.1042/bj1670121.

Abstract
  1. 5-Cholesten-3-one was shown to be an intermediate in the conversion of cholesterol into 4-cholesten-3-one by Nocardia cholesterol oxidase. 2. The absence of a C-17 side chain from 5-androstene-3,17-dione slightly increased the Vmax. of the isomerase activity relative to 5-cholesten-3-one (1.7-fold), but greatly increased the Km. 3. Incubations of [4alpha-2H]-and [4beta-2H]-cholesterol with cholesterol oxidase showed that the 4beta-hydrogen atom can be transferred to the 6beta-position. However, incubations of cholesterol, 5-cholesten-3-one and 4-cholesten-3-one with the enzyme in 2H2O led to some incorporation of 2H into the 4-cholesten-3-one products, mostly at position 6beta. 4. Both the isomerase and the oxidase activities of cholesterol oxidase were inhibited by 5,10-seco-19-nor-5-cholestyne-3,10-dione.
摘要
  1. 5-胆甾烯-3-酮被证明是诺卡氏菌胆固醇氧化酶将胆固醇转化为4-胆甾烯-3-酮过程中的一个中间体。2. 与5-胆甾烯-3-酮相比,5-雄烯-3,17-二酮缺少C-17侧链,其异构酶活性的Vmax略有增加(1.7倍),但Km大大增加。3. 用胆固醇氧化酶对[4α-2H]-和[4β-2H]-胆固醇进行孵育表明,4β-氢原子可转移至6β-位。然而,在2H2O中用该酶对胆固醇、5-胆甾烯-3-酮和4-胆甾烯-3-酮进行孵育,导致4-胆甾烯-3-酮产物中有一些2H掺入,主要在6β-位。4. 5,10-开环-19-降-5-胆甾炔-3,10-二酮可抑制胆固醇氧化酶的异构酶和氧化酶活性。

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