Characterization and sequence determination of six aprotinin homologues from bovine lungs.

Six Kunitz inhibitors, which are dissimilar to aprotinin, can be isolated from bovine lungs. These homologues cannot be distinguished from aprotinin, in respect to their inhibitory specificity. They have, however, different amino-acid compositions and a different degree of basicity. The entire primary structures of these inhibitors were elucidated by automated Edman sequencing. Besides the known Glp-1-aprotinin another aprotinin homologue (des-Ala58-aprotinin) was isolated, which could result from a different proteolytic processing of the bovine aprotinin precursor. The other homologues can be denoted as aprotinin isoinhibitors, showing several amino-acid replacements compared to aprotinin and which also appear in the area of the contact region.