Bile acid acyl adenylate: a possible intermediate to produce a protein-bound bile acid

The non-enzymatic production of a protein-bound adduct by the action of the acyl adenylate of bile acids is described. On incubation of deoxycholyl ad enylate with substance P in phosphate buffer, peptides covalently bound wit h one or two molecules of the bile acid were detected. The modified peptide s were structurally characterized by time-of-flight mass spectrometry with matrix-assisted laser desorption/ionization (MALDI-TOFMS) in the post-sourc e decay mode, and by liquid chromatography/electrospray ionization MS/MS. T he deoxycholic acid was bound on substance P through the amino group at Arg -1 and/or Lys-3. The adenylate of cholic acid also produced the protein-bou nd bile acid on incubation with lysozyme, and the binding sites of the chol ic acid appeared to be the lysine residues at 1, 33, 97 and 116. The result s clearly suggest that bile acid adenylates in vivo may act as active inter mediates to produce covalently bound bile acid adducts with peptides and pr oteins by nucleophilic displacement of the 5'-adenylic acid through the fre e amino groups. Copyright (C) 2001 John Wiley & Sons, Ltd.