title: Specific lysine labeling by 18OH- during alkaline cleavage of the alpha-1-antitrypsin-trypsin complex.
abstract: alpha-1-Antitrypsin is a serum protein that inhibits many proteolytic enzymes. Recently, it was suggested that the alpha-1-antitrypsin-trypsin complex is an acyl ester analogous to the acyl intermediate that forms between trypsin and its substrates. In previous work we showed that the alpha-1-antitrypsin-trypsin complex can be split at high pH, releasing a component of alpha-1-antitrypsin. This component had a new carboxyl-terminal lysine, and it had lost a peptide of about 4000 daltons. In order to determine whether the alpha-1-antitrypsin is bound to trypsin through the new carboxy-terminal lysine, as would be expected if the above hypothesis is correct, we split the complex in the presence of 18OH-. When the new carboxy-terminal lysine was cleaved with carboxypeptidase B, singly labeled, doubly labeled, and unlabeled lysine were recovered. These data support the hypothesis that the alpha-1-antitrypsin-trypsin complex is an acyl ester or a tetrahedral precursor that is transformed into the acyl ester form at high pH. If other enzymes are bound by a similar mechanism, the methods used may be useful in determining which amino acids on alpha-1-antitrypsin bind covalently to each enzyme.
mesh_terms: D000468:Alkalies; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D006868:Hydrolysis; D008239:Lysine / Q000031:analogs & derivatives / Q000032:analysis*; D010103:Oxygen Isotopes; D011485:Protein Binding; D013552:Swine; D014357:Trypsin / Q000378:metabolism*; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
chemical_list: D000468:Alkalies; D000596:Amino Acids; D010103:Oxygen Isotopes; D000515:alpha 1-Antitrypsin; D014357:Trypsin; D008239:Lysine