title: Activation of human C1r: Western blot analysis reveals slow and dose-dependent activation.
abstract: Spontaneous activation of C1r in the presence of EDTA was examined by a Western blot. Partially purified native C1r was prepared by ultracentrifugation of fresh serum in 10 to 30% sucrose gradient; final concentration of C1r was one-sixth of the original serum. C1(-)-INH was not detectable by a single radial immunodiffusion (less than 0.5% of serum). The results demonstrated that 1) the rate of spontaneous activation of C1r was slow (less than 10% in 30 min); 2) it was concentration-dependent; 3) it was enhanced by activated C1r; and 4) it was almost completely suppressed by serine protease inhibitors up to 1 h. These results were inconsistent with an intramolecular autoactivation model of C1r in the fluid phase and suggested intermolecular activation by contaminating protease or activated C1r.
authors.affiliation: Laboratory of Immunobiology, National Cancer Institute, Frederick, MD 21701.
authors.forename: S
authors.initials: S
authors.lastname: Hosoi
authors.forename: T
authors.initials: T
authors.lastname: Borsos
mesh_terms: D000328:Adult; D002384:Catalysis; D002499:Centrifugation, Density Gradient; D003166:Complement Activating Enzymes / Q000302:isolation & purification / Q000378:metabolism*; D003167:Complement Activation; D003172:Complement C1 / Q000302:isolation & purification / Q000378:metabolism*; D015923:Complement C1r; D003171:Complement Pathway, Classical; D004306:Dose-Response Relationship, Immunologic; D004492:Edetic Acid; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007700:Kinetics; D015842:Serine Proteinase Inhibitors
chemical_list: D003172:Complement C1; D015842:Serine Proteinase Inhibitors; D004492:Edetic Acid; D003166:Complement Activating Enzymes; D015923:Complement C1r