Comparative specificity of microbial acid proteinases for synthetic peptides. 3. Relationship with their trypsinogen activating ability

The specificities of acid proteinases from Aspergillus niger, Aspergillus saitoi, Rhizopus chinensis, Mucor miehei, Rhodotorula glutinis, and Cladosporium sp., and that of swine pepsin, were determined and compared with ability of the enzymes to activate trypsinogen. Various oligopeptides containing l-lysine, Z-Lys-X-Ala, Z-Lys-(Ala)_m, Z-Lys-Leu-(Ala)₂, and Z-(Ala)_n-Lys-(Ala)₃ (X = various amino acid residues, m = 1–4, n = 1–2) were used as substrates. Of the enzymes which are able to activate trypsinogen, most split these peptides at the peptide bond formed by the carbonyl group of l-lysine. For the peptides to be susceptible to the enzymes it was essential that the chain extended for two or three amino acid residues on the C-terminal side of the catalytic point, and that a bulky or hydrophobic amino acid residue formed the imino-side of the splitting point. The rate of hydrolysis was markedly accelerated by elongation of the peptide chain with l-alanine on the N-terminal side of the catalytic point. Thus, of the substrates used, Z-(Ala)₂-Lys-(Ala)₃ was the most susceptible to the microbial acid proteinases possessing trypsinogen activating ability. On the other hand, M. miehei enzyme and pepsin, which do not activate trypsinogen, showed very little peptidase activity on the peptides.