Purification and some properties of three serine carboxypeptidases from Aspergillus niger

Three enzymes exhibiting peptidyl-L-amino acid hydrolase and esterase activities have been purified by immobilized metal-ion affinity chromatography and ion-exchange chromatography. The three enzymes were entirely free of the acid protease activity that normally exists along with them in the crude culture filtrates of Aspergillus niger. Although all three exo-peptidases possessed nearly identical molecular weights (ca. 140,000), isoelectric points (ca. 5.0) and other properties, their affinities for the two substrates tested, carbobenzoxy-L-Glu-L-Tyr and benzoyl L-arginine ethyl ester, differed. All three peptidases were inhibited by phenylmethanesulphonyl fluoride, indicating that they are serine carboxypeptidases. They were also inhibited by tosyl phenylalanine chloromethyl ketone, suggesting the presence of a histidyl residue in their active sites. The differences in the number of accessible histidyl residues on the enzyme surfaces could explain the differences in their retentions on Cu2+-iminodiacetate-Sepharose 6B.