Automated assay for α₁-antitrypsin with N-α-benzoyl-DL-arginine-p-nitroanilide as trypsin substrate and standardized with p-nitrophenyl-p'-guanidinobenzoate as titrant for trypsin active sites

α₁-Antitrypsin is the most abundant of several serum protease inhibitors. Its deficiency is associated with an increased incidence of emphysema in adults, jaundice in newborns, and childhood cirrhosis. The authors describe an automated functional assay for the Instrumentation Laboratory's Multistat III Microcentrifugal Analyzer with N-α-benzoyl-DL-arginine-p-nitroanilide as trypsin substrate. The assay is standardized in terms of moles of trypsin active sites inhibited per liter of serum, by use of a chromogenic titrant for trypsin active sites, p-nitrophenyl-p'-guanidinobenzoate. The method is rapid, precise, and independent of trypsin supplier, and results correlate well with those by a manual chromogenic and a nephelometric assay.