D-alanyl-D-alanine carboxypeptidase in the bacterial form and L-form of Proteus mirabilis

Eur J Biochem. 1975 Jul 1;55(2):465-73. doi: 10.1111/j.1432-1033.1975.tb02183.x.


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.

MeSH terms

  • Alanine
  • Carboxypeptidases / metabolism*
  • Cell Membrane / drug effects
  • Cell Membrane / enzymology
  • D-Amino-Acid Oxidase
  • Detergents / pharmacology
  • Hydrogen-Ion Concentration
  • Kinetics
  • L Forms / enzymology*
  • Penicillin G / pharmacology
  • Penicillin V / pharmacology
  • Proteus mirabilis / enzymology*
  • Protoplasts / enzymology
  • Spheroplasts / enzymology


  • Detergents
  • D-Amino-Acid Oxidase
  • Carboxypeptidases
  • Alanine
  • Penicillin G
  • Penicillin V