title: A new simple method for determination of C1-esterase inhibitor activity in plasma.
abstract: A convenient method for the determination of C1-esterase inhibitor activity in plasma samples is described. The method is based on addition of purified C1s to plasma and measuring excess C1s with a new chromogenic tripeptide-p-nitroanilide substrate with a recording spectrophotometer. Addition of C1s to C1-esterase inhibitor-depleted plasma did not result in any appreciable inactivation of the enzyme for three hours. The concentration of C1-esterase inhibitor in 19 healthy individuals was estimated as 1.63 +/- 0.27 (SD) mumol/l. The correlation with C1-esterase inhibitor antigen in these individuals and 19 patients with varying concentrations of C1-esterase inhibitor was excellent. The correlation with an antikallikrein assay was found to be poor.
mesh_terms: D003166:Complement Activating Enzymes / Q000378:metabolism; D003174:Complement C1 Inactivator Proteins / Q000097:blood* / Q000276:immunology; D003173:Complement C1s; D006801:Humans; D007610:Kallikreins / Q000037:antagonists & inhibitors; D008722:Methods; D009842:Oligopeptides / Q000378:metabolism; D012016:Reference Values; D013053:Spectrophotometry
chemical_list: D003174:Complement C1 Inactivator Proteins; D009842:Oligopeptides; D003166:Complement Activating Enzymes; D007610:Kallikreins; D003173:Complement C1s