title: Evolution of alpha 2-macroglobulin. The purification and characterization of a protein homologous with human alpha 2-macroglobulin from plaice (Pleuronectes platessa L.) plasma.
abstract: A papain-binding protein (PB-protein) was purified to homogeneity from the plasma of plaice (Pleuronectes platessa L.). PB-protein inhibited the activity of trypsin and pancreatic elastase (serine proteinases), thermolysin (a metalloproteinase) and papain (a cysteine proteinase). Presaturation of PB-protein with trypsin prevented the subsequent inhibition of thermolysin, and vice versa. Only catalytically active endopeptidases were bound by PB-protein. The catalytic activity of trypsin bound by PB-protein was inhibited by 95% against an insoluble protein substrate, but only by 38% against a low-molecular-weight synthetic substrate. The remaining activity of the bound trypsin was partially protected against further inhibition by soya-bean trypsin inhibitor. Trypsin bound by PB-protein showed a decrease of 67% in its reactivity with antibodies. The inhibitory activity of PB-protein was inactivated at pH 8.0 by methylamine (0.2M) or dithiothreitol (1 mM). The inhibition of proteinases by plaice PB-protein shows the distinctive characteristics of inhibition by human alpha 2-macroglobulin, and it is concluded that the plaice protein is a homologue of the human macroglobulin.
mesh_terms: D000818:Animals; D001665:Binding Sites; D005075:Biological Evolution; D002352:Carrier Proteins / Q000032:analysis; D002850:Chromatography, Gel; D004229:Dithiothreitol / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism; D005399:Fishes / Q000097:blood*; D008744:Methylamines / Q000494:pharmacology; D010206:Papain / Q000378:metabolism; D013820:Thermolysin / Q000378:metabolism; D014357:Trypsin / Q000276:immunology / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000032:analysis*
chemical_list: D002352:Carrier Proteins; D008744:Methylamines; D000511:alpha-Macroglobulins; C027451:methylamine; D010450:Endopeptidases; D014357:Trypsin; D010206:Papain; D013820:Thermolysin; D004229:Dithiothreitol