Amino Acid Sequence of an Alkaline Proteinase Inhibitor (Streptomyces Subtilisin Inhibitor) from Streptomyces albogriseolus S-32531

Streptornyces subtilisin inhibitor was reduced and carboxymethylated and then cleaved with cyanogen bromide. As expected, four fragments were isolated and some of them were further degraded with trypsin [EC 3.4.21.4], chymotrypsin [EC 3.4.21.1], thermolysin [EC 3.4.24.4], and collagenase [EC 3.4.24.3]. The sequences of these fragments and the resulting peptides were determined by conventional methods, establishing the complete 113 amino acid sequence of the inhibitor. Fragmentation of the native inhibitor with cyanogen bromide showed that one of the two disulfide bridges was located between Cys (35) and Cys (50), and the other between Cys (71) and Cys (101). Sequence data showed extremely high concentrations of alanine, proline, leucine, and threonine residues in the first half of the protein, indicating some unusual aspects of the structure of the inhibitor molecule. Examination of the results revealed that residues 67 through 85 of Streptomyces inhibitor are clearly homologous with residues 12 through 29 of bovine pancreatic secretory trypsin inhibitor (Kazal's inhibitor) which includes the trypsin-reactive site of Kazal's inhibitor. The possible reactive site of Streptomyces subtilisin inhibitor is discussed.