title: Characteristics of complement subcomponents C1r and C1s synthesized by Hep G2 cells.
abstract: The association and activation states of complement subcomponents C1r and C1s biosynthesized by Hep G2 cells were studied. C1r and C1s are secreted in stoichiometric amounts; in the presence of Ca2+ they are associated in a complex that sediments similarly to plasma C1r2-C1s2. Both compounds are synthesized as monomer proteins of apparent Mr 86 000. C1r is secreted as a dimer. Secreted C1r is not autoactivatable but undergoes proteolysis by exogenous C1r; secreted C1s is also proteolysed by exogenous C1r. In the presence of immune-complex-bound C1q, secreted C1r and C1s are able to reconstitute C1, but normal activation requires extrinsic C1r2-C1s2.
mesh_terms: D000818:Animals; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D011232:Chemical Precipitation; D003166:Complement Activating Enzymes / Q000096:biosynthesis* / Q000276:immunology; D015923:Complement C1r; D003173:Complement C1s; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000032:analysis
chemical_list: D046911:Macromolecular Substances; D010446:Peptide Fragments; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003173:Complement C1s