Low pH stability of alpha-1-antititrypsin.

According to the previous findings of others, the trypsin inhibitory capacity of alpha-1-antitrypsin is irreversibly lost in acidic solutions below pH 5.0. In contrast, experiments reported herein show that considerable inhibitory activity can be regenerated as a time-dependent phenomena following titration to basic media. The rate of recovery of activity is accompanied by a decreasing amplitude in the fluorescent emission spectrum at 335 nm of acidified alpha-1-antitrypsin solutions following adjustment to pH 8.0. Acidic media also results in the slow, progressive formation of protein aggregates as measured using Sephadex gel filtration. This latter process is more prominent at pH 4.0, near the isoelectric point of alpha-1-antitrypsin than at pH 3 or 2. Both monomer and polymeric forms of alpha-1-antititrypsin were isolated before or after adjustment to basic media. Isolated monomeric material shows a high recovery of biological and immunological activity; aggregate forms, however, are immunologically cross-reactive but show little enzyme inhibitory activity.