Interaction between β-Lactam Antibiotics and Exocellular DD-Carboxypeptidase-Transpeptidase of <em>Streptomyces</em> R61.

On the basis of steady-state kinetics, inhibition of the exocellular DD-carboxypeptidase-transpeptidase 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 8. min at 370C and neutral pH. During breakdown of the complexes the protein underwent reactivation, whereas the released antibiotic molecule was chemically altered. With [14C]benzylpenicillin, the released compound was neither benzylpenicillin nor benzylpenicillin acid. The properties of the Streptomyces R61 enzyme β-lactam antibiotic complexes were compared with those of the complexes formed between the same antibiotic and either the membrane-bound transpeptidase from Streptomyces R61 or the exocellular DD-carboxypeptidase-transpeptidase of Streptomyces R39. [ABSTRACT FROM AUTHOR]