title: Active-site-directed inactivators of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase of Streptomyces albus G.
abstract: Several types of active-site-directed inactivators (inhibitors) of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase were tested. (i) Among the heavy-atom-containing compounds examined, K2Pt(C2O4)2 inactivates the enzyme with a second-order rate constant of about 6 X 10(-2)M-1 X S-1 and has only one binding site located close to the Zn2+ cofactor within the enzyme active site. (ii) Several compounds possessing both a C-terminal carboxylate function and, at the other end of the molecule, a thiol, hydroxamate or carboxylate function were also examined. 3-Mercaptopropionate (racemic) and 3-mercaptoisobutyrate (L-isomer) inhibit the enzyme competitively with a Ki value of 5 X 10 X 10(-9)M. (iii) Classical beta-lactam compounds have a very weak inhibitory potency. Depending on the structure of the compounds, enzyme inhibition may be competitive (and binding occurs to the active site) or non-competitive (and binding causes disruption of the protein crystal lattice). (iv) 6-beta-Iodopenicillanate inactivates the enzyme in a complex way. At high beta-lactam concentrations, the pseudo-first-order rate constant of enzyme inactivation has a limit value of 7 X 10(-4)S-1 X 6-beta-Iodopenicillanate binds to the active site just in front of the Zn2+ cofactor and superimposes histidine-190, suggesting that permanent enzyme inactivation is by reaction with this latter residue.
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors*; D006046:Gold / Q000494:pharmacology; D007495:Iridium / Q000494:pharmacology; D008670:Metals / Q000494:pharmacology*; D008958:Models, Molecular; D010984:Platinum / Q000494:pharmacology; D013302:Streptomyces / Q000201:enzymology*; D014501:Uranium / Q000494:pharmacology; D014961:X-Ray Diffraction
chemical_list: D008670:Metals; D007495:Iridium; D010984:Platinum; D014501:Uranium; D006046:Gold; D002268:Carboxypeptidases; C033455:zinc D-Ala-D-Ala carboxypeptidase