Abstract
The specificity of the serine carboxypeptidase from Aspergillus saitoi (EC 3.4.16.1) was investigated on carboxyterminal amidated peptides such as benzyloxycarbonyl(Z)-Ala-Phe-NH2, gastrin-related peptide, molluscan cardioexcitatory neuropeptide, eledoisin-related peptide, and (D-Ala2, Met5)-enkephalinamide. The enzyme did not hydrolyze Z-Ala-Phe-NH2. It acted only as a carboxyamidase for the carboxyterminal peptide bond of gastrin-related peptide and as an amidase for enkephalinamide. The enzyme had both carboxyamidase activity and amidase activity for molluscan cardioexcitatory neuropeptide and eledoisin-related peptide.
Whether the enzyme acts as an amidase or carboxyamidase, the hydrophobicity of P3 and P4 positions of the substrate may be important. After removal of the carboxyterminal amino acid amide and/or ammonia, the enzyme catalyzed the sequential liberation of the amino acid from the carboxyterminus of the substrate.
