Macdonald I A, Hutchison D M, Forrest T P
J Lipid Res. 1981 Mar;22(3):458-66.
Eight strains of Clostridium absonum were shown to form ursocholic acid (UC) from cholic acid (C) and ursodeoxycholic acid (UDC) from chenodeoxycholic acid (CDC) but did not transform deoxycholic acid (DC) in whole cell cultures. The structures of UC and UDC were verified by mass spectroscopy, and by thin-layer chromatography using Komarowsky's spray reagent. The organism transformed C and CDC at concentrations below 1.5. 10(-3) M and 5.0. 10(-4) M, respectively; higher concentrations were inhibitory. Optimal yields of the final products were realized at about 15-22 hr and 9-15 hr of incubation, respectively, and were in the range of 60-70%. Additionally, the 7 keto-derivatives, 7 keto-deoxycholic acid (7K-DC) or 7 keto-lithocholic acid (7K-LC) were also formed from C and CDC. With longer periods of incubation, increasing yields of 7K-DC and 7K-LC and decreasing yields of UC and UDC were observed. These time course studies suggest that 7K-DC and 7K-LC are intermediates in the formation of UC and UDC from the primary bile acids. We propose the occurrence of C right harpoon over left harpoon 7K-DC right harpoon over left harpoon UC and CDC right harpoon over left harpoon 7K-LC right harpoon over left harpoon UDC with increasing dominance of back reaction of the second step on aging of the culture. When the initial pH value of the medium was manipulated within the range of 5.8-9.0, increasing yields of UDC from CDC were obtained at higher pH values (maximum yield at pH 9.0 was 83%), with total inhibition of growth and transformation at pH 5.8. In contrast, UC was produced from C at all pH values studied, with marginal differences in yields (maximum yield at pH 8.0 was 50%). In all cases, formation of UC from C was much slower than that of UDC from CDC. In contrast, C. paraperfringens transformed none of the above bile acids. We propose that C. absonum, or a biochemically similar species, may be present in the human gut and give rise to UDC (and UC) in vivo.-Macdonald, I. A., D. M. Hutchison, and T. P. Forrest. Formation of urso- and ursodeoxycholic acids from primary acids by Clostridium absonum.
研究表明，八株奇异梭菌可将胆酸（C）转化为熊去氧胆酸（UC），并将鹅去氧胆酸（CDC）转化为熊脱氧胆酸（UDC），但在全细胞培养中不会转化脱氧胆酸（DC）。UC和UDC的结构通过质谱以及使用科马罗夫斯基喷雾试剂的薄层色谱法进行了验证。该微生物分别在浓度低于1.5×10⁻³ M和5.0×10⁻⁴ M时转化C和CDC；较高浓度具有抑制作用。最终产物的最佳产量分别在培养约15 - 22小时和9 - 15小时时实现，产量范围在60% - 70%。此外，还从C和CDC中形成了7 - 酮衍生物，即7 - 酮脱氧胆酸（7K - DC）或7 - 酮石胆酸（7K - LC）。随着培养时间延长，观察到7K - DC和7K - LC产量增加，而UC和UDC产量降低。这些时间进程研究表明，7K - DC和7K - LC是由初级胆汁酸形成UC和UDC的中间体。我们提出随着培养老化第二步逆反应的优势增加，存在C右叉左叉7K - DC右叉左叉UC以及CDC右叉左叉7K - LC右叉左叉UDC的反应过程。当培养基的初始pH值在5.8 - 9.0范围内变化时，在较高pH值下从CDC获得的UDC产量增加（pH 9.0时最大产量为83%），在pH 5.8时生长和转化完全受到抑制。相比之下，在所研究的所有pH值下均由C产生UC，产量差异不大（pH 8.0时最大产量为50%）。在所有情况下，由C形成UC的速度比由CDC形成UDC的速度慢得多。相比之下，产气荚膜梭菌不会转化上述任何一种胆汁酸。我们推测奇异梭菌或生化特性相似的菌种可能存在于人体肠道中，并在体内产生UDC（和UC）。 - 麦克唐纳，I. A.，D. M. 哈钦森，和T. P. 福里斯特。奇异梭菌从初级酸形成熊去氧胆酸和熊脱氧胆酸。
