Two peptides released in the complex formation of alpha 1-antitrypsin with beta-trypsin; evidence for two structurally identical, inhibitory sites in alpha 1-antitrypsin.

The exact mechanism of action of alpha 1-antitrypsin, the major protease inhibitor in human serum, is still unknown. Several investigators report the release of a small peptide during complex formation of alpha 1-antitrypsin with various proteases. In this study the release of two peptides each from the NH2- and the COOH-terminal regions of alpha 1-antitrypsin is demonstrated, indicating the presence of two inhibitory sites in alpha 1-antitrypsin. The amino acid sequence near the NH2-terminal inhibitory site is determined to be X-Ser-Ile-Pro-Pro- and near the COOH-terminal inhibitory site Y-Ala-Ile-Pro-Met-Ser-Ile-Pro. The combined results of the present report and several other reports indicate the presence of two structurally identical inhibitory sites in alpha 1-antitrypsin located at both terminal regions in the molecule.