ω‐Hydroxylation of Steroid Side‐Chain in Biosynthesis of Bile Acids
ω‐Hydroxylation of Steroid Side‐Chain in Biosynthesis of Bile Acids
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胆汁酸生物合成中类固醇侧链的 ω-羟基化
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发表时间：
1973
期刊：
影响因子：
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通讯作者：
J. Gustafsson
中科院分区：
文献类型：
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作者：
I. Björkhem;J. Gustafsson
研究了微粒体和线粒体组分对各种C10-甾体的邻羟基化（26-羟基化）。以5-胆甾烷-3a，7a-二醇为底物，确定了微粒体26-羟基化的测定条件。NADPH是所需的辅因子。在次优浓度的NADPH下，NADH刺激羟基化。一氧化碳对羟基化反应有明显的抑制作用。苯巴比妥治疗抑制反应，而饥饿或胆道引流没有显着影响。以nmol/mg蛋白质/20分钟表示的不同C12-甾体的微粒体26-羟基化速率为胆固醇<0.1; 5-异戊烯-3 β，7 α-二醇，<0.1; 7 α-羟基-4-异戊烯-3-酮，0.3; 7 α，12 α-二羟基-4-异戊烯-3-酮，0.9; 5 β-异戊烯胆甾烷-3a，7a-二醇，1.8; 5/？-胆甾烷-3 α，7 α，12 α-三醇，2.7。以胆固醇和5-胆甾烷-3a，7a-二醇为底物，确定了线粒体26-羟基化的测定条件。NADPH生成系统的反应速率比NADPH快。一氧化碳可明显抑制该反应。胆汁引流抑制反应，而饥饿或苯巴比妥治疗没有显着影响。以nmol/mg蛋白每20分钟表达的不同C12-甾体的线粒体26-羟基化速率为：胆固醇，0.3; 5-β-甾烯-3 β，7-二醇，0.9; 7 α-羟基-4-甾烯-3-酮，1.7; 7 α，12 α-二羟基-4-甾烯-3-酮，0.9; 5 β-甾烯-3 β，7 α-二醇，0.9; 5 β-羟基-4-甾烯-3-酮，1.7; 12 α-羟基-4-甾烯-3-酮，1.7; 12 α胆甾烷-3a，7 α-二醇，0.9; 5~-胆甾烷-3a，7 α，12 α-三醇，2.0。结果与先前假设的关于胆酸和鹅去氧胆酸生物合成的途径一致，其中5/？-胆甾烷-3a，7a，12n-trio1和5/？-胆甾烷3 α，7 α-二醇分别是26-羟化酶的主要底物。本文还讨论了胆汁酸生物合成途径中7 α，26-二羟基-4-甾烯-3-酮和7 α，12 α，26-三羟基-4-甾烯-3-酮的中间产物的可能性。
o-Hydroxylation (26-hydroxylation) of various C,,-steroids by the microsomal and mitochondrial fraction was studied. Assay conditions for the microsomal 26-hydroxylation were determined with 5~-cholestane-3a,7a-diol as substrate. NADPH was the required cofactor. NADH stimulated the hydroxylation at suboptimal concentrations of NADPH. The hydroxylation was inhibited markedly by carbon monoxide. Treatment with phenobarbital inhibited the reaction whereas starvation or biliary drainage had no significant effect. The rates of microsomal 26-hydroxylation of different C,,-steroids expressed in nmol/mg protein per 20 min were cholesterol, < 0.1 ; 5-cholestene-3#?,7a-diol, < 0.1 ; 7a-hydroxy-4-cholesten-3-one, 0.3 ; 7a,12a-dihydroxy-4-cholesten-3-one, 0.9 ; 5/?-cholestane-3a,7a-diol, 1.8 ; 5/?-cholestane-3a,7a,i2a-triol, 2.7. Assay conditions for the mitochondrial 26-hydroxylation were determined with cholesterol and 5~-cholestane-3a,7a-diol as substrates. The rate of reaction was faster with an NADPHgenerating system than with NADPH. The reaction was inhibited markedly with carbon monoxide. Biliary drainage inhibited the reaction whereas starvation or treatment with phenobarbital had no significant effect. The rates of mitochondrial 26-hydroxylation of different C,,-steroids expressed in nmol/mg protein per 20 min were : cholesterol, 0.3 ; 5-cholestene-3p,7adiol, 0.9 ; 7a-hydroxy-4-cholesten-3-one, 1.7 ; 7a,12a-dihydroxy-4-cholesten-3-one, 0.9 ; 5/?-cholestane-3a,7aw-diol, 0.9 ; 5~-cholestane-3a,7a,l2a-triol, 2.0. The results are consistent with previously postulated pathways concerning biosynthesis of cholic acid and chenodeoxycholic acid in which 5/?-cholestane-3a,7a, 12n-trio1 and 5/?-cholestane3a,7a-diol, respectively are the main substrates for the 26-hydroxylase. The possibility is discussed that pathways involving intermediary formation of 7a,26-dihydroxy-4-cholesten-3-one and 7a,12a,26-trihydroxy-4-cholesten-3-one also are of importance in the biosynthesis of bile acids.