Streptomyces R61 dd-carboxypeptidase: Hydrolysis of X-d-alanyl-d-alanine peptides measured by a fluorometric assay

A fluorometric procedure for measuring the activity of dd-carboxypeptidase is described. The method is based on the reaction of one of the products, d-alanine, with o-phthaldialdehyde to form a highly fluorescent adduct. The method has been applied in examining a series of X-d-alanyl-d-alanine peptides as substrates of the penicillin-sensitive dd-carboxypeptidase from Streptomyces R61. The effect of the third residue, X, on kinetic parameters and its implications on the steric analog model for penicillin action are also discussed.