DD-Carboxypeptidase activity of membrane fragments of Mycobacterium smegmatis. Enzymatic properties and sensitivity to beta-lactam antibiotics.

A DD-carboxypeptidase activity is present in membrane fragments of Mycobacterium smegmatis. Kinetic parameters of the enzymatic activity have been studied using UDP-N-glycolylmuramyl-L-alanyl-gamma-D-glutamyl-meso-2,2'-diaminopimelyl-D-[14C]alanyl-D-[14C]alanine as substrate. The DD-carboxypeptidase can be solubilized by Triton X-100 and Genapol X-100. It is inhibited by beta-lactam antibiotics although intact cells of M. smegmatis are insensitive to that kind of antibiotics. Inhibition by penicillin G is slowly reversible. By storage, at -20degrees C, kinetic parameters and sensitivity to penicillin G vary non-concomittantly, suggesting a penicillin binding site different from the substrate binding site.