Purification and characterization of serine carboxypeptidases from Absidia zychae

Among 29 strains of zygomycetes screened for serine carboxypeptidases, Absidia zychae NRIC 1199 showed the highest enzyme production. Two serine carboxypeptidases, CPZ-1 and CPZ-2, were purified to a homogeneous state from an extract of koji culture of A. zychae NRIC 1199. Purified CPZ-1 and CPZ-2 showed similar properties except the isoelectric point (pI); The pI of CPZ-1 and CPZ-2 were 4.50 and 4.65, respectively. The molecular weights of the CPZ-1 and CPZ-2 were 48,000 by SDS-PAGE and gel filtration. Among the proteinase inhibitors tested, phenylmethylsulfonyl fluoride and monoiodoacetic acid strongly inhibited the enzyme activity. The optimum pHs of CPZ-1 and CPZ-2 were 4.2 towards Z-Glu-Tyr. It is shown that the substrate specificities of CPZ-1 and CPZ-2 were dependent on the presence of bulky amino acid residues in the penultimate position (P1) for the small Z-peptides. However, in spite of the presence of Gly, Asp, Arg, or Pro in the P1 position, oligopeptides were hydrolyzed rapidly. CPZ-1 and CPZ-2 had not only carboxypeptidase but also carboxyamidase and amidase activities, and acted preferentially as a carboxyamidase for C-terminal amidated peptides. The hydrophobicity of P2 and P3 positions and the bulkiness of P1 and P'1 positions of the substrate may be important for carboxyamidase and amidase activities.