The co-purification and common identity of cholyl CoA:glycine- and cholyl CoA:taurine-N-acyltransferase activities from bovine liver.

A procedure for the purification of cholyl CoA:glycine and taurine N-acyltransferase activities from the soluble cell fraction of bovine liver is described. The procedure results is an 900-fold enrichment relative to the soluble cell fraction. The final preparation gives a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Mr = 50,900, and runs as a single peak, Mr = 47,000, on gel filtration. The preparation is approximately 80% pure as judged by isoelectric focusing and focuses at a pH of 6.6. The glycine and taurine conjugating activities co-purified and did not separate to any extent in any of the chromatographic steps employed, including a gradient elution from an affinity column and an isoelectric focusing column. Also, kinetic analysis revealed that glycine and taurine appear to compete for a common active site. The two activities had identical temperature-denaturation curves and were equivalently stabilized against temperature denaturation by taurocholate. This data provides strong evidence for a common enzyme for both glycine and taurine conjugation in bovine liver. A preliminary kinetic characterization of the enzyme revealed non-Michaelis-Menten kinetics.