title: Effects of cadmium on manganese peroxidase competitive inhibition of MnII oxidation and thermal stabilization of the enzyme.
abstract: Inhibition of manganese peroxidase by cadmium was studied under steady-state and transient-state kinetic conditions. CdII is a reversible competitive inhibitor of MnII in the steady state with Ki approximately 10 microM. CdII also inhibits enzyme-generated MnIII-chelate-mediated oxidation of 2,6-dimethoxyphenol with Ki approximately 4 microM. CdII does not inhibit direct oxidation of phenols such as 2,6-dimethoxyphenol or guaiacol (2-methoxyphenol) in the absence of MnII. CdII alters the heme Soret on binding manganese peroxidase and exhibits a Kd approximately 8 microM, similar to Mn (Kd approximately 10 microM). Under transient-state conditions, CdII inhibits reduction of compound I and compound II by MnII at pH 4.5. However, CdII does not inhibit formation of compound I nor does it inhibit reduction of the enzyme intermediates by phenols in the absence of MnII. Kinetic analysis suggests that CdII binds at the MnII-binding site, preventing oxidation of MnII, but does not impair oxidation of substrates, such as phenols, which do not bind at the MnII-binding site. Finally, at pH 4.5 and 55 degrees C, MnII and CdII both protect manganese peroxidase from thermal denaturation more efficiently than CaII, extending the half-life of the enzyme by more than twofold. Furthermore, the combination of half MnII and half CdII nearly quadruples the enzyme half-life over either metal alone or either metal in combination with CaII.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Beaverton, Oregon 97006-8921, USA.
authors.forename: H L
authors.initials: HL
authors.lastname: Youngs
authors.forename: M
authors.initials: M
authors.lastname: Sundaramoorthy
authors.forename: M H
authors.initials: MH
authors.lastname: Gold
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002104:Cadmium / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D005656:Fungal Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D006207:Half-Life; D006358:Hot Temperature; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D020075:Phanerochaete / Q000201:enzymology; D011485:Protein Binding; D011489:Protein Denaturation / Q000187:drug effects; D011748:Pyrogallol / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D007527:Isoenzymes; D002104:Cadmium; D011748:Pyrogallol; D008345:Manganese; C010120:pyrogallol 1,3-dimethyl ether; D010544:Peroxidases; C051129:manganese peroxidase; D002118:Calcium