title: Purification and characterization of a carboxypeptidase-transpeptidase of Bacillus megaterium acting on the tetrapeptide moiety of the peptidoglycan.
abstract: The enzyme carboxypeptidase-IIW of Bacillus megaterium incorporates free diaminopimelate into purified bacterial walls. This enzyme can be solubilized from toluene-treated cells by LiCl extraction and has now been purified 106-fold to one major band on polyacrylamide gel electrophoresis. The enzyme has an apparent molecular weight of approximately 60,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Sephadex G-100 gel filtration. Carboxypeptidase-IIW requires divalent cations and thiol group(s) for optimal activity. Product analysis indicates that the enzyme can hydrolyze the terminal D-alanine from the tetrapeptide of the peptidoglycan or replace it with a variety of amino acids with D-asymmetric centers for transpeptidation. Substrate specificity studies reveal that the enzymatic activity depends on the presence of N-acetyl-D-glucosamine of the GlcNAc-MurNAc-tetrapeptide. This specificity of carboxypeptidase-IIW for the N-acetyl-D-glucosamine explains in part the affinity of the enzyme for the cell wall of B. megaterium. The enzyme is compared to the carboxypeptidases-transpeptidases of other organisms with the similarities and differences discussed.
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D000409:Alanine; D001410:Bacillus megaterium / Q000201:enzymology*; D002268:Carboxypeptidases / Q000302:isolation & purification / Q000378:metabolism*; D002413:Cations, Divalent; D007700:Kinetics; D010457:Peptidoglycan / Q000378:metabolism*; D010458:Peptidyl Transferases / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity; D013379:Substrate Specificity; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D010457:Peptidoglycan; D013439:Sulfhydryl Reagents; D000217:Acyltransferases; D010458:Peptidyl Transferases; D002268:Carboxypeptidases; D000409:Alanine