title: The identification of a previously unrecognized subcomponent of the first component of complement.
abstract: The use of an affinity chromatography method designed to isolate C1 from serum has led to the discovery of a novel plasma protein, II-P2, associated with C1. The persistent Ca++-dependent association of II-P2 with C1 subcomponents following euglobulin precipitation, affinity chromatography on Sepharose-IgG, and density gradient ultracentrifugation indicates that II-P2 might be a C1 subcomponent. Using purified preparations of II-P2 it was found that a) II-P2 was retained on Sepharose-IgG through a Ca++-dependent link with C1q,b) II-P2 enhanced the C1 activity of mixtures of C1s and C1q in a dose-dependent fashion, c) II-P2 bound firmly to EAC1q4 cells and enhanced their C1s-binding ability. Fractionation of C1 by DEAE-Cellulose chromatography under the conditions that led to the original identification of C1q, C1r, and C1s resulted in recovery of II-P2 in the fractions containing C1r. The evidence presented confirms that II-P2 is a C1 subcomponent (C1t).
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D002499:Centrifugation, Density Gradient; D002846:Chromatography, Affinity; D002848:Chromatography, DEAE-Cellulose; D003172:Complement C1 / Q000032:analysis*; D003165:Complement System Proteins / Q000032:analysis*; D004586:Electrophoresis; D004592:Electrophoresis, Starch Gel; D005362:Ficoll; D007106:Immune Sera; D005779:Immunodiffusion; D011506:Proteins / Q000032:analysis; D011817:Rabbits / Q000276:immunology
chemical_list: D003172:Complement C1; D007106:Immune Sera; D011506:Proteins; D005362:Ficoll; D003165:Complement System Proteins