title: The exocellular DD-carboxypeptidase-endopeptidase of Streptomyces albus G. Interaction with beta-lactam antibiotics.
abstract: Kinetically, the three-step model proposed for the interaction between beta-lactam antibiotics and the exocellular DD-carboxypeptidases-transpeptidases of Streptomyces R61 and Actinomadura R39 [Frère, Ghuysen & Iwatsubo (1975) Eur. J. Biochem. 57, 343--357; Fuad, Frère, Ghuysen, Duez & Iwatsubo (1976) Biochem. J. 155, 623--629] applies to the interaction between the much less penicillin-sensitive exocellular DD-carboxypeptidase-endopeptidase of Streptomyces albus G and at least phenoxymethylpenicillin, cephalothin and cephalosporin C. The penicillin resistance of the albus G enzyme is mainly due to the low efficiency with which the first reversible complex formed with the antibiotic (complex EI) undergoes transformation into a second more stable complex EI*. Analysis of the ternary interaction between enzyme, NalphaNepsilon-diacetyl-L-lysyl-D-alanyl-D-alanine (Ac2-L-Lys-D-Ala-D-Ala) and cephalosporin C indicates a non-competitive mechanism.
mesh_terms: D000409:Alanine; D002511:Cephalosporins / Q000494:pharmacology*; D002512:Cephalothin / Q000494:pharmacology; D004150:Dipeptidases; D004151:Dipeptides; D010450:Endopeptidases / Q000378:metabolism; D005110:Extracellular Space / Q000201:enzymology; D007700:Kinetics; D008956:Models, Chemical; D010403:Penicillin Resistance; D010404:Penicillin V / Q000494:pharmacology*; D013302:Streptomyces / Q000187:drug effects / Q000201:enzymology*
chemical_list: D002511:Cephalosporins; D004151:Dipeptides; D010450:Endopeptidases; D004150:Dipeptidases; C019989:DD-carboxypeptidase-endopeptidase; D000409:Alanine; D002512:Cephalothin; D010404:Penicillin V