title: Regulation of the activation of C1 in serum.
abstract: C1 has been partially purified from serum and its ability to activate has been studied. The activation status of C1 was measured using a sensitive hemolytic assay which allowed the activation status of C1 in serum to be monitored. C1 did not activate in serum but would spontaneously activate when separated from certain other serum proteins, in particular, the C1-inhibitor protein. The activation of C1 was time and concn dependent, but addition of fully activated C1 did not affect either the rate or extent of activation. The activation of C1 could be inhibited reversibly by C1-inhibitor. This action of the C1-inhibitor was over and above its ability to regulate fully activated C1 by covalent bond formation with either the serine esterase of C1s or C1r. The results presented suggest that the C1-inhibitor plays a dual role in the regulation of C1 activation. The regulatory actions of C1-inhibitor would account for the presence of C1 in a zymogen form and for the episodic nature of complement consumption observed in individuals with genetic deficiencies of the C1-inhibitor protein.
authors: Department of Immunology and Medical Microbiology, College of Medicine, University of Florida, Gainesville 32610.
authors: E L
authors: EL
authors: Faulmann
authors: M D
authors: MD
authors: Boyle
mesh_terms: D002852:Chromatography, Ion Exchange; D003167:Complement Activation; D003172:Complement C1 / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D003174:Complement C1 Inactivator Proteins / Q000494:pharmacology; D004306:Dose-Response Relationship, Immunologic; D006461:Hemolysis; D006801:Humans
chemical_list: D003172:Complement C1; D003174:Complement C1 Inactivator Proteins