Activation of the C1 complex is under control of the C1-inhibitor. It forms a proteolytically inactive stoichiometric complex with the C1r or C1s proteases. May play a potentially crucial role in regulating important physiological pathways including complement activation, blood coagulation, fibrinolysis and the generation of kinins. Very efficient inhibitor of FXIIa. Inhibits chymotrypsin and kallikrein. Binds to E.coli stcE which allows localization of SERPING1 to cell membranes thus protecting the bacteria against complement-mediated lysis. Interacts with MASP1. Highly glycosylated (49%) with N- and O-glycosylation. O-glycosylated with core 1 or possibly core 8 glycans. N-glycan heterogeneity at Asn-25: Hex5HexNAc4 (minor), dHex1Hex5HexNAc4 (minor), Hex6HexNAc5 (major) and dHex1Hex6HexNAc5 (minor). Can be proteolytically cleaved by E.coli stcE. Chymotrypsin uses Ala-465 as its reactive site in normal plasma protease C1 inhibitor, and His-466 as its reactive site in the variant His-466. The disease is caused by variants affecting the gene represented in this entry. Belongs to the serpin family. C1-inhibitor entry SERPING1 mutation db