Jean-Marie Frere

Synthetic peptide inhibitors of transpeptidation by the exocellular DD-carboxypeptidase-transpeptidase from Actinomadura R39

The penicillin-sensitive exocellular carboxypeptidases-transpeptidases of Actinomycetes have been extensively studied as models of peptidoglycan construction and modification in relation to their mode of enzyme action and their mechanism of inhibition by fl-lactam antibiotics [ 1,2]. The enzyme from Actinomadura R39 has been purified to homogeneity [3] and is known to catalyse hydrolysis of the C-terminal D-alanyl-D-alanine peptide bound in natural and synthetic substrates (e.g., Acz-L-Lys-D-AlaD-Ala) or, in the presence of a suitable acceptor, to perform transpeptidation in which an acceptor moiety such as meso-diaminopimelic acid (A, pm) replaces the terminal D-alanine [4]. The amount of transpeptidation relative to carboxypeptidase action in a particular digest was highly sensitive to the concentration of a ‘natural’ acceptor: