Rapid screening for deficiency of α1-proteinase inhibitor

Abstract

This rapid screening procedure for detection of low but functional elastase-inhibitory activity in human plasma is based on the fact that incubation of excess porcine pancreatic elastase (EC 3.4.21.36) with plasma results in formation of a complex with active α1-proteinase inhibitor (α1PI, also called α1-antitrypsin). In normal individuals all of the elastase is complexed, leaving no free enzyme to hydrolyze the elastase substrate, and the reaction mixture remains clear. Because individuals homozygous for the Z allele have relatively low concentrations of α1PI, their plasma cannot complex all of the elastase in the assay. The uncomplexed enzyme hydrolyzes the elastase-specific p-nitroanilide substrate, producing a yellow reaction mixture. Use of this simple assay for early screening of individuals for α1PI deficiency may substantially decrease the number of untreated cases of familial emphysema, a disorder that develops as a result of a genetically derived proteinase-proteinase inhibitor imbalance.