Summary: The Dpcarboxypeptidase of was exclusively associated with the proto-plast membrane. The enzyme had a pH optimum of 4.9 and was sensitive to thiol reagents. The D, D-carboxypeptidase was stimulated by most divalent cations, Pb and Cd providing the greatest degree of activation, but it was inhibited by Hg and Fe. A particulate L, D-carboxypeptidase was demonstrated in membrane preparations which were also able to catalyse a simple transpeptidation reaction employing D-alanine as the carboxyl acceptor. An endopeptidase activity capable of liberating D-alanyl-D-alanine from UDP-N-acetylmuramyl-L-Alanyl-y-γ-D-glutamy--2,6-diaminopimelyl-D-alanyl-D-alanine (UDP-MurNAc-pentapeptide) was present in the cytoplasm. This appeared to be the reverse reaction of the D-alanyl-D-alanine-adding enzyme responsible for the generation of the peptidoglycan precursor UDP-MurNAc-pentapeptide.


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