title: Heparin-stimulated modification of C1-inhibitor by subcomponent C1s of human complement.
abstract: C1-inhibitor and C1s form a very stable complex which migrates with an apparent molecular mass of 180 kDa in dodecyl sulfate gel electrophoresis. A small fraction of the inhibitor (100 kDa) was found to be converted to a large (95 kDa) and a small (2 to 5 kDa) fragment during this reaction. It is concluded that C1-inhibitor is modified by C1s in a similar way as are the related plasma inhibitors alpha 1-proteinase inhibitor, antithrombin III and antiplasmin by their specific proteinases. The fraction of modified C1-inhibitor increased when heparin was present during complex formation. This reaction was complete after 15 s and is comparable with the fast heparin induced formation of modified antithrombin III. Treatment with hydroxylamine led to a complete dissociation of the inhibitor-enzyme complex by dodecyl sulfate. The large inhibitor fragment (and not unmodified inhibitor as reported by other authors) was released.
mesh_terms: D003166:Complement Activating Enzymes; D003174:Complement C1 Inactivator Proteins / Q000032:analysis*; D003173:Complement C1s; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D006898:Hydroxylamines
chemical_list: D003174:Complement C1 Inactivator Proteins; D006898:Hydroxylamines; D006493:Heparin; D003166:Complement Activating Enzymes; D003173:Complement C1s