J. Biol. Chem., Vol. 261, Issue 14, 6260-6263, 05, 1986
Structural characterization of cholylcoenzyme A:glycine-taurine N- acyltransferase and a covalent substrate intermediate
B Czuba and DA Vessey
Bile acid-CoA:glycine-taurine N-acyltransferase was found to catalyze a
reaction in the absence of glycine or taurine in which the substrate
cholyl-CoA is cleaved with the release of CoA and the formation of a
covalently bound enzyme-cholate intermediate. This unstable intermediate
was trapped by a rapid mixing and denaturation procedure. The denatured
protein was digested with trypsin and the cholate-labeled tryptic peptide
was isolated. This cholate-peptide is considered to originate from the
active site region of the enzyme based on the following criteria:
cholyl-CoA does not react with any of the 20 common amino acids, the
hydrolysis of cholyl-CoA is known to occur on the enzyme, the lack of
reaction of the enzyme with just cholate, and the fact that labeling is
extensive even at low (substrate level) concentrations of cholyl-CoA. The
isolated cholate-peptide was submitted to amino acid analysis. It contained
32 amino acid residues and was devoid of cysteine, methionine, and
tyrosine. Amino acid analysis of the N-acyltransferase was conducted. The
enzyme was also shown to possess a blocked N terminus.