title: Pro-C4 of human plasma: isolation and description of chemical and antigenic properties.
abstract: The fourth component of complement (C4) occurs in human plasma as a protein with a three polypeptide chain structure. Lately a single-chain form of C4 has been purified from human plasma by sequential steps of immunoadsorbent chromatography, gel filtration in 6 M guanidine hydrochloride, and gel filtration in 6 M guanidine hydrochloride and 0.015 M dithiothreitol. Single-chain C4, referred to as pro-C4, behaved as a protein of approximately 200,000 daltons upon gel filtration, and was separated from the three chains of C4 on the basis of molecular size. Pro-C4 could be isolated from each of five human plasmas examined and was found to constitute approximately 2% of total, immunoreactive C4. Replicate amino acid analyses of pro-C4 and C4 agreed within 0.5 mol % for all residues except glycine and threonine, which agreed within 0.7 mol percent. Polyacrylamide gel electrophoresis of pro-C4 in the presence of sodium dodecyl sufate in 5% gels under reducing conditions indicated an approximate molecular weight of 202,000. The sum of the molecular weights of the alpha-, beta-, and gamma-chain of C4 is 205,000. After gel electrophoresis, pro-C4 stained positively with periodic acid-Schiff reagent, suggesting the presence of covalently-bound carbohydrate. Competitive inhibition radioimmune assays with pro-C4, purified alpha-, beta-, or gamma-chain, and chain-specific antisera demonstrated the existence of antigenic sites on pro-C4 that are assignable to common determinants on each of the alpha-, beta-, and gamma-chains of C4.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D003181:Complement C4 / Q000276:immunology / Q000302:isolation & purification; D000939:Epitopes; D006041:Goats / Q000276:immunology; D006801:Humans; D007106:Immune Sera; D046911:Macromolecular Substances; D008970:Molecular Weight; D011498:Protein Precursors / Q000276:immunology / Q000302:isolation & purification; D011863:Radioimmunoassay
chemical_list: D000596:Amino Acids; D003181:Complement C4; D000939:Epitopes; D007106:Immune Sera; D046911:Macromolecular Substances; D011498:Protein Precursors