The function of SERPING1 (serpin family G member 1, ENSG00000149131) is as follows. Serine protease inhibitor, which acrs as a regulator of the classical complement pathway (PubMed:10946292, PubMed:11527969, PubMed:3458172, PubMed:6416294). Forms a proteolytically inactive stoichiometric complex with the C1r or C1s proteases (PubMed:10946292, PubMed:3458172, PubMed:6416294). May also regulate blood coagulation, fibrinolysis and the generation of kinins (PubMed:8495195). Very efficient inhibitor of FXIIa. Inhibits chymotrypsin and kallikrein (PubMed:8495195). {ECO:0000269|PubMed:10946292, ECO:0000269|PubMed:11527969, ECO:0000269|PubMed:3458172, ECO:0000269|PubMed:6416294, ECO:0000269|PubMed:8495195}.