title: Mouse alpha-macroglobulin. Structure, function and a molecular model.
abstract: Mouse alpha-macroglobulin (M-AMG) is believed to be a functional homologue of human alpha 2-macroglobulin (h-alpha 2M). The subunit composition, the tryptic cleavage pattern before and after methylamine incorporation and the two-dimensional tryptic-peptide mapping, however, indicate that these two proteins are structurally distinct. M-AMG is composed of two major types of polypeptides (Mr 163,000 and 35,000) together with a minor polypeptide (Mr 185,000), whereas h-alpha 2M has only one type of polypeptide (Mr 185,000). After incorporation of methylamine, there is no change in the normal tryptic-cleavage pattern of M-AMG; however, tryptic cleavage of h-alpha 2M is severely retarded [Hudson & Koo (1982) Biochim. Biophys. Acta 704, 290-303]. The N-terminal sequence of the 163,000-Mr polypeptide of M-AMG shows sequence homology with the N-terminal sequence of h-alpha 2M. The amino acid compositions of M-AMG and its two major polypeptide chains are compared. Thermal fragmentation studies show that the 163,000-Mr polypeptide is broken down into 125,000-Mr and 29,000-Mr fragments. Trypsin-binding studies show that M-AMG can bind two molecules of trypsin/molecule. Inactivations of the trypsin-binding property of M-AMG and h-alpha 2M with methylamine show similar kinetics of inhibition at 4 degrees C. A structural model of M-AMG is proposed, based on accumulated data.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000911:Antibodies, Monoclonal; D001665:Binding Sites; D004591:Electrophoresis, Polyacrylamide Gel; D008744:Methylamines / Q000494:pharmacology; D051379:Mice; D008809:Mice, Inbred C3H; D008954:Models, Biological; D010449:Peptide Mapping; D011487:Protein Conformation; D014357:Trypsin / Q000494:pharmacology; D014361:Trypsin Inhibitors / Q000494:pharmacology; D000511:alpha-Macroglobulins / Q000037:antagonists & inhibitors
chemical_list: D000596:Amino Acids; D000911:Antibodies, Monoclonal; D008744:Methylamines; D014361:Trypsin Inhibitors; D000511:alpha-Macroglobulins; C027451:methylamine; D014357:Trypsin