Cholic acid conjugating enzyme system

In preliminary experiments he found that neither nuclear nor mitochondrial fractions were necessary for conjugation of cholic acid to taurine. These fractions rather inhibited the conjugation. The recombination of microsomes and soluble fraction (for definition see Section II,C) in the presence of ATP yielded the same conjugation capacity as homogenates. Each of these fractions alone, hoivever, had no conjugation capacity. From those experiments he concluded that the cholic acid conjugating enzyme system must be localized to the microsomes and/or to the soluble fraction and that the same also must be valid for some unknow n cofaetor(s). 

The conjugation of bile acids with added hydroxylamine by rat liver microsomes in the presence of ATP, CoA, and fluoride to yield bile acid hydroxamates has been used to demonstrate the formation of cholyl-CoA as an intermediate in the enzymatic system catalyzing the synthesis of the natural conjugates (12,13). In pig liver, there appear to be two distinctly different enzyme systems capable of the synthesis of cholylhydroxamic acid (15). A partially solubilized preparation from pig liver catalyzed the rapid formation of cholylhydroxamic acid in the presence of cholic acid and hydroxylamine but in the absence of ATP and CoA. This is in contrast to the synthesis of hydroxamates of bile acids by the microsomes, which required both ATP and CoA. Since fluoride inhibits the system that functions in the absence of ATP and CoA, the reaction appears to be similar to that of a lipase (15)... 

In mammalian liver parenchyma cells, the synthesis of the steroid skeleton which was described on p. 236 is extended by acquisition of an enzyme system leading to the production of the substances known as bile acids. In man, this s3mthesis yields cholic acid, desoxycholic acid and chenodesoxycholic acid. The hepatic parenchyma in mammals also conjugates these bile acids with taurine and with glycine. 

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