title: Plasmic degradation of human fibrinogen. III. Molecular model of the plasmin-resistant disulfide knot in monomeric fragment D.
abstract: A mixture of fragments D, derived from fibrinogen by plasmic degradation, was S-reduced and carboxymethylated. Individual chains were separated by gel filtration on Sephadex G-100 and characterized by peptide mapping, N-terminal amino acid analysis, polyacrylamide electrophoresis in sodium dodecyl sulfate, and amino acid composition. It was demonstrated that all D species contain the same alpha- and beta-chain remnants, having mol. wts of 10 000 and 45 000, respectively. Their heterogeneity was shown to be caused by the gradual degradation of the gamma-chain at its C-terminal end. Denatured fragment D was further degraded with plasmin in the presence of 2 M urea. One beta- (mol. wt 17 000) and two gamma-fragments (mol. wts 5000 and 6000) were split from fragment D, in addition to non-characterized small peptides, leaving behind a plasmin-resistant core, designated as fragment d. Fragment d was in turn reduced and carboxymethylated, and the resulting constituent chains were isolated by chromatography on carboxymethyl-cellulose and Sephadex G-100. The reduced alpha-, beta- and gamma-chain remnants of fragment d were found to have been derived from the N-terminal portion of fragment D and have estimated mol. wts of 9000, 24 000 and 13 000, respectively. A tentative scheme for the conversion of an early fragment D into the core fragment d is proposed. Our results conclusively support the model of asymmetric degradation of fibrinogen, according to which 2 mol of monomeric fragment D are produced from 1 mol of fibrinogen.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001665:Binding Sites; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D004220:Disulfides / Q000032:analysis; D005340:Fibrinogen / Q000378:metabolism; D005341:Fibrinolysin; D006801:Humans; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D014508:Urea
chemical_list: D000596:Amino Acids; D004220:Disulfides; D010446:Peptide Fragments; D014508:Urea; D005340:Fibrinogen; D005341:Fibrinolysin