Pii: 0014-5793(75)80810-6

North-Holland Publishing Company Amsterdam of glycine of another hexapeptide, so that dimers or trimers (or rarely higher polymers) are built up [ 1 ] . The location of the physiological transpeptidase appears to be the plasma membrane [4]. An exocellular enzyme has been isolated from Streptomyces R6 1 and shown to have DD-carboxypeptidase and transpeptidase activities [ S-81. The enzyme was shown to catalyse the formation of a D-Ala-Gly peptide bond, such as is found in the native, completed wall peptidoglycan. An example of such a reaction is the transformation of Aca-LLys-D-Ala-D-Ala and Gly-LAla into Aca-LLys-D-Ala-Gly-L-Ala and D-alanine. In this report, it is shown that the tetrapeptide, p-[ l4 C] Ac-NE-(Gly)LLys-D-Ala-D-Ala, can serve as both donor and acceptor substrate of this enzyme, yielding several products, including one containing more than one D-Ala-Gly interpeptide linkage.