The source of a minor alpha 1-antitrypsin in variant serum.

An antiserum produced against human alpha1-antitrypsin gave 2 precipitin lines by immunodiffusion when tested against sera displaying MZ or MS phenotypes. Only one line (major antigen) was seen with sera displaying M phenotype, but a second line (minor antigen) became evident when the serum was concentrated 5-fold. The minor antigen appeared to be a denatured form of alpha1-antitrypsin, because the major antigen was converted to the minor one when purified alpha1-antitrypsin was incubated between pH 2.95 and 4.0. Such incubation inactivated the protein irreversibly. The purified protein was also inactivated completely within 1 hour at pH 4.95, but the activity was recovered completely by incubation for 2 to 4 hours at pH 8.0. The immunologic properties of the reactivated a1-antitrypsin were the same as those of the original untreated protein.