Hylemon P B, Melone P D, Franklund C V, Lund E, Björkhem I
Department of Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
J Lipid Res. 1991 Jan;32(1):89-96.
We previously reported that the 7 alpha-dehydroxylation of cholic acid appears to be carried out by a multi-step pathway in intestinal anaerobic bacteria both in vitro and in vivo. The pathway is hypothesized to involve an initial oxidation of the 3 alpha-hydroxy group and the introduction of a double bond at C4-C5 generating a 3-oxo-4-cholenoic bile acid intermediate. The loss of water generates a 3-oxo-4,6-choldienoic bile acid which is reduced (three steps) yielding deoxycholic acid. We synthesized, in radiolabel, the following putative bile acid intermediates of this pathway 7 alpha,12 alpha-dihydroxy-3-oxo-4-cholenoic acid, 7 alpha,12 alpha-dihydroxy-3-oxo-5 beta-cholanoic acid, 12 alpha-dihydroxy-3-oxo-4,6-choldienoic acid, and 12 alpha-hydroxy-3-oxo-4-cholenoic acid and showed that they could be converted to 3 alpha,12 alpha-dihydroxy-5 beta-cholanoic acid (deoxycholic acid) by whole cells or cell extracts of Eubacterium sp. VPI 12708. During studies of this pathway, we discovered the accumulation of two unidentified bile acid intermediates formed from cholic acid. These bile acids were purified by thin-layer chromatography and identified by gas-liquid chromatography-mass spectrometry as 12 alpha-hydroxy-3-oxo-5 alpha-cholanoic acid and 3 alpha,12 alpha-dihydroxy-5 alpha-cholanoic (allo-deoxycholic acid). Allo-deoxycholic acid was formed only in cell extracts prepared from bacteria induced by cholic acid, suggesting that their formation may be a branch of the cholic acid 7 alpha-dehydroxylation pathway in this bacterium.
我们之前报道过，胆酸的7α-脱羟基作用在体外和体内的肠道厌氧细菌中似乎是通过多步途径进行的。据推测，该途径涉及3α-羟基的初始氧化以及在C4-C5处引入双键，生成3-氧代-4-胆烯酸胆汁酸中间体。水的脱去生成3-氧代-4,6-胆二烯酸，其经过三步还原生成脱氧胆酸。我们用放射性标记合成了该途径的以下假定胆汁酸中间体：7α,12α-二羟基-3-氧代-4-胆烯酸、7α,12α-二羟基-3-氧代-5β-胆烷酸、12α-二羟基-3-氧代-4,6-胆二烯酸和12α-羟基-3-氧代-4-胆烯酸，并表明它们可被真杆菌属VPI 12708的全细胞或细胞提取物转化为3α,12α-二羟基-5β-胆烷酸（脱氧胆酸）。在对该途径的研究过程中，我们发现了由胆酸形成的两种未鉴定的胆汁酸中间体的积累。这些胆汁酸通过薄层色谱法纯化，并通过气-液色谱-质谱法鉴定为12α-羟基-3-氧代-5α-胆烷酸和3α,12α-二羟基-5α-胆烷酸（别-脱氧胆酸）。别-脱氧胆酸仅在由胆酸诱导的细菌制备的细胞提取物中形成，这表明它们的形成可能是该细菌中胆酸7α-脱羟基途径的一个分支。
