Identification of a unique mammalian species of cholyl-CoA: amino acid N-acyltransferase.

The N-acyltransferase enzyme which catalyzes the conjugation of the CoA adducts of bile acids with amino acid has been partially purified from dog liver. Unlike the N-acyltransferase from five other mammalian species, the enzyme from dog liver was unable to synthesize glycine conjugates from cholyl-CoA in vitro even in the presence of 0.1 M glycine. The enzyme did catalyse the synthesis of taurine conjugates. Thus, the enzyme from dog liver resembles non-mammalian forms of the enzyme which also synthesize only taurine conjugates. However, the molecular weight of the enzyme from dog liver was found to be approximately 45 700, which is similar to values reported for other mammalian forms and considerably smaller than the molecular weight of 65 000 reported previously for a non-mammalian form of the enzyme.