title: Purification of the membrane-bound DD-carboxypeptidase of the unstable spheroplast L-form of Proteus mirabilis by affinity chromatography. Non-competitive inhibition of the enzyme by penicillins and low stability of the enzyme-inhibitor complex.
abstract: Membrane-bound DD-carboxypeptidase of the unstable L-form of Proteus mirabilis was solubilized by the non-ionic detergent Genapol X-100 and purified to protein homogeneity by affinity chromatography on ampicillin bound to succinyl-aminododecyl-cellulose. The purified enzyme with a molecular weight of 43000 is inhibited non-competitively by penicillin G and carbenicillin, indicating a function of the penicillins as allosteric inhibitors. Sensitivity of the enzyme to penicillins is only moderate with a Ki of 1 muM for penicillin G. Breakdown of.the enzyme-inhibitor complex EI with different penicillins occurs rapidly with reappearance of active DD-carboxypeptidase. The half-life of EI with penicillin G is 5.5 min at 30 degrees C and 3.5 min at 37 degrees C, 10--1000-fold shorter than EI half-lives of DD-carboxypeptidases in several other bacteria. The low stability of the enzyme-inhibitor complex and the moderate penicillin sensitivity appear to be the basis for the continued activity of DD-carboxypeptidase during growth of the L-form and synthesis of peptidoglycan in the presence of high concentrations of penicillin.
mesh_terms: D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D002846:Chromatography, Affinity / Q000379:methods*; D004591:Electrophoresis, Polyacrylamide Gel; D007740:L Forms / Q000201:enzymology*; D008970:Molecular Weight; D010400:Penicillin G / Q000494:pharmacology; D010403:Penicillin Resistance; D011513:Proteus mirabilis / Q000187:drug effects / Q000201:enzymology*; D013104:Spheroplasts / Q000201:enzymology*
chemical_list: D002268:Carboxypeptidases; D010400:Penicillin G