Kinetics of Interaction between the Exocellular DD-Carboxypeptidase-Transpeptidase from Streptomyces R61 and β-Lactam Antibiotics.

The simplest model for the interaction between the exocellular DD-carboxypeptidase-transpeptidase from Streptomyces R61 and β-lactam antibiotics involves the three following steps: (a) the formation of a reversible equimolar enzyme, antibiotic complex; (b) the irreversible transformation of this complex into a modified enzyme antibiotic complex; and (c) the breakdown of this latter complex and the concomitant release of a regenerated enzyme and a modified antibiotic molecule. The dissociation constant for step 1 and the rate constants for steps 2 and 3 were measured with various β-lactam antibiotics. With an antibiotic such as benzylpenicillin, which behaves as a good 'substrate', steps 1 and 2 occur at enzymic velocities, whereas step 3 occurs at a very low velocity and hence is responsible for the low efficiency of the overall process. [ABSTRACT FROM AUTHOR]