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

Eur J Biochem. 1978 Nov 15;91(2):501-7. doi: 10.1111/j.1432-1033.1978.tb12703.x.

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 Gaffkya homari. These amino acids inhibited the incorporation of nascent peptidoglycan into the preformed polymer (e.g. ID50 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. It is suggested that the reaction is catalyzed by an LD-carboxypeptidase. Therefore, this enzyme has also D-amino acid exchange activity. At inhibitory concentration fewer tripeptide subunits were formed in the nascent peptidoglycan in favour of the formation of tetrapeptide subunits bearing the inhibitor at the C 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.

MeSH terms

  • Carboxypeptidases / metabolism*
  • Cell Membrane / enzymology
  • Cell Wall / metabolism
  • Glycine
  • Kinetics
  • Muramic Acids
  • Peptidoglycan / biosynthesis*
  • Stereoisomerism
  • Streptococcaceae / enzymology*
  • Substrate Specificity

Substances

  • Muramic Acids
  • Peptidoglycan
  • Carboxypeptidases
  • Glycine