title: Formation and dissociation of the covalent complexes between trypsin and two homologous inhibitors, alpha 1-antitrypsin and antithrombin III.
abstract: The mechanisms by which alpha 1-antitrypsin and antithrombin III inhibit trypsin were investigated by chemical stability studies and amino acid sequence analyses of the enzyme-inhibitor complexes. One-to-one covalently linked complexes were formed between each of the inhibitors and trypsin. The complexes were stable over the course of the experiments at pH 8 or lower, and benzamidine, hydroxylamine, thiols, guanidine, or dodecyl sulfate had no apparent effect on the stability of the complexes. The complexes dissociated slowly at pH 9 or greater. Neither of the inhibitors was active after dissociation from its complex with trypsin. Sequence analysis indicated that no new amino terminus was generated when alpha 1-antitrypsin formed its complex with trypsin, but that two new amino termini were formed in approximately one-to-one ratio when the complex dissociated. This may indicate that alpha 1-antitrypsin contains two inhibitory sites for trypsin in close spatial proximity on the molecule.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000990:Antithrombin III / Q000378:metabolism*; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006863:Hydrogen-Ion Concentration; D012967:Sodium Dodecyl Sulfate; D013552:Swine / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism*; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
chemical_list: D000515:alpha 1-Antitrypsin; D012967:Sodium Dodecyl Sulfate; D000990:Antithrombin III; D014360:Trypsin Inhibitor, Kunitz Soybean; D014357:Trypsin