Interaction between β‐Lactam Antibiotics and Exocellular dd‐Carboxypeptidase‐Transpeptidase of Streptomyces R61

On the basis of steady‐state kinetics, inhibition of the exocellular dd ‐carboxypeptidase‐trans‐peptidase of Streptomyces R61 by β‐lactam antibiotics was competitive with regard to the donor substrate. However, the complexes formed between the Streptomyces R61 enzyme and various β‐lactam antibiotics were relatively stable, exhibiting half‐lives of 40 to 80 min at 37°C and neutral pH. During breakdown of the complexes the protein underwent reactivation, whereas the released antibiotic molecule was chemically altered. With [ 14 C]benzylpenicillin, the released compound was neither benzylpenicillin nor benzylpenicilloic acid. The properties of the Streptomyces R61 enzyme β‐lactam antibiotic complexes were compared with those of the complexes formed between the same antibiotics and either the membrane‐bound transpeptidase from Streptomyces R61 or the exocellular dd ‐carboxypeptidase‐transpeptidase of Streptomyces R39.