D-alanyl-D-alanine carboxypeptidase in the bacterial form and L-form of Proteus mirabilis.
Membranes of the bacterial form and the stable and unstable L-forms of Proteus mirabilis contain LD and DD-carboxypeptidase. The DD-carboxypeptidase is inhibited non-competitively by penicillin G. The enzyme of the bacterial form is highly penicillin-sensitive (Ki - 4 X 10(-9) M penicillin G). Inhibition is only partly reversible by treatment with penicillinase or by dialysis against buffer. In contrast, the DD-carboxypeptidase of the unstable L-form, grown in the presence of penicillin, is 175-fold less penicillin-sensitive (Ki = 7 X 10(7) M penicillin G). Inhibition is completely reversed by penicillinase or dialysis. After inhibition by penicillin and subsequent reactivation the penicillin sensitivity of the bacterial DD-carboxtpeptidase is similar to the sensitivity of the enzyme of the unstable L-form. The hypothesis is proposed that P. mirabilis contains two DD-carboxypeptidases of different penicillin sensitivity and with different mechanisms of penicillin binding. Peptidoglycan synthesis in the cell walls of the unstable L-form is probably carried out with the help of only one DD-carboxypeptidase, viz. the completely reactivatable enzyme with the lower penicillin sensitivity.
D000409:Alanine; D002268:Carboxypeptidases / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D003605:D-Amino-Acid Oxidase; D003902:Detergents / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007740:L Forms / Q000201:enzymology*; D010400:Penicillin G / Q000494:pharmacology; D010404:Penicillin V / Q000494:pharmacology; D011513:Proteus mirabilis / Q000201:enzymology*; D011523:Protoplasts / Q000201:enzymology; D013104:Spheroplasts / Q000201:enzymology
D003902:Detergents; D003605:D-Amino-Acid Oxidase; D002268:Carboxypeptidases; D000409:Alanine; D010400:Penicillin G; D010404:Penicillin V