PURIFICATION AND CHARACTERIZATION OF BILE ACID-COA - AMINO-ACID N-ACYLTRANSFERASE FROM RAT-LIVER

  • 1 January 1978
    • journal article
    • research article
    • Vol. 253  (4) , 1005-1010
Abstract
An in vitro study of bile acid-CoA:amino acid N-acyltransferase activity of rat liver was undertaken in order to determine whether separate amino acid-specific enzymes catalyzed the formation of glycine and taurine conjugates of bile acids as postulated by others.Polyacrylamide gel electrophoresis of 200-fold purified enzyme localized the glycine- and taurine-dependent activities to a single band. Both activities were optimal at pH 7.8 and showed similar loss of activity at pH 6.0, pH 9.0, in the presence of 5,5''-dithiobis(2-nitrobenzoic acid), and at temperatures exceeding 50.degree. C. With the purified fraction, Km for glycine was 31 mM and Km for taurine was 0.8 mM. Km for several bile acid-CoA substrates was .apprx. 20 .mu.M and independent of the amino acid acceptor. Only amino acids with terminal .alpha.- or .beta.-amino groups were active as acyl acceptors. Acyl donors were limited to bile acid-CoA derivatives. The rat may have a single bile acid-CoA:amino acid N-acyltransferase. The substrate kinetics are consistent with previous observations that taurine conjugates predominate in rat bile at normal hepatocellular concentrations of glycine and taurine.