title: Characterization of alkylamine-sensitive site in alpha 2-macroglobulin.
abstract: Methylamine reacts with the plasma protease inhibitor, alpha 2-macroglobulin, to form an irreversible, covalent modification. Quantitation of the reaction indicates 3.9 +/- (SD) 0.4 reactive sites per native tetrameric protein (Mr = 725,000) or one site per subunit. The reaction is selective and specific in that only 1 or 2 labeled peptides are observed on radioautography of peptide maps derived from [14C]methylamine-treated alpha 2-macroglobulin. A single chymotryptic peptide was isolated in 56% overall yield from the labeled protein. The peptide sequence by Edman degradation was found to be Gly-Cys-Gly-Glu-X-Asn-Met-(Val, Leu), in which X was the only radiolabeled phenylthiohydantoin derivative. Amino acid analysis and mass spectral analysis of the derivative suggests that X is gamma-glutamylmethylamide. Because glutamic acid and glutamine residues do not normally react with alkylamines, this work presents presumptive evidence for an alternative activated center in selected proteins.
mesh_terms: D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D005971:Glutamates; D006801:Humans; D008744:Methylamines / Q000494:pharmacology; D010446:Peptide Fragments / Q000032:analysis; D011480:Protease Inhibitors / Q000037:antagonists & inhibitors; D000511:alpha-Macroglobulins / Q000037:antagonists & inhibitors
chemical_list: D005971:Glutamates; D008744:Methylamines; D010446:Peptide Fragments; D011480:Protease Inhibitors; D000511:alpha-Macroglobulins