The penicillin-binding site in the exocellular DD-carboxypeptidase-transpeptidase of Actinomadura R39

Heat denaturation and Pronase degradation of the complex previously formed between benzylpenicillin and the exocellular DD-carboxypeptidase-transpeptidase of Actinomadura R39 yields a heptapeptide H-Leu-Pro-Ala-Ser-Asn-Gly-Val-OH, where the benzylpenicilloyl group is ester-linked to the serine residue. This linkage is very labile and its hydrolysis causes the release of benzylpenicilloate. In contrast, the native benzylpenicilloyl-enzyme complex is very stable (half-life 70h at 370C) and its
breakdown proceeds via fragmentation of the bound benzylpenicilloyl group [Fuad, Frere, Ghuysen, Duez & Iwatsubo (1976) Biochem. J. 155, 623-6291.