The LD-Carboxypeptidase Activity in Gaffkya homari. The Target of the Action of d-Amino Acids or Glycine on the Formation of Wall-Bound Peptidoglycan

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Abstract
The effects in vitro of D-amino acids or glycine on the formation of wall-bound peptidoglycan were studied with wall membrane enzyme preparations from G. homari [Aerococcus viridans]. These amino acids inhibited the incorporation of nascent peptidoglycan into the preformed polymer (e.g., ID50 [median inhibition dose] values for D-alanine, D-leucine and glycine = 5.6 mmol/l, 1.3 mmol/l and 11 mmol/l, respectively). The inhibition was accompanied by an incorporation of the inhibitor into position 4 of the peptide subunit Ala1-DGlu2(Lys3-DAla4), where the indices refer to the position of an amino acid residue within the peptide subunit. The reaction may be catalyzed by an LD-carboxypeptidase [EC 3.4.4.12.-]. This enzyme has also D-amino acid exchange activity. At inhibitory concentration fewer tripeptide subunits were formed in the nascent peptidoglycan in favor of the formation of tetrapeptide subunits bearing the inhibitor at the C [carboxyl] termini. The tripeptide subunits are assumed to be necessary in order that nascent peptidoglycan is utilized as substrate in the transpeptidation reaction. Thus an essential role of the LD-carboxypeptidase is indicated.