Modified microperoxidases exhibit different reactivity towards phenolic substrates.
The reactivity of several microperoxidase derivatives with different distal-site environments has been studied. The distal-site environments of these heme peptides include a positively charged one, an uncharged environment, two bulky and doubly or triply positively charged ones, and one containing aromatic apolar residues. The reactivity in the catalytic oxidation of two representative phenols, carrying opposite charges, by hydrogen peroxide has been investigated. This allows the determination of the binding constants and of the electron-transfer rate from the phenol to the catalyst in the substrate/microperoxidase complex. The electron-transfer rates scarcely depend on the redox and charge properties of the phenol, but depend strongly on the microperoxidase. Information on the disposition of the substrate in the adducts with the microperoxidases has been obtained through determination of the paramagnetic contribution to the 1H NMR relaxation rates of the protons of the bound substrates. The data show that the electron-transfer rate drops when the substrate binds too far away from the iron and that the phenols bind to microperoxidases at similar distances to those observed with peroxidases. While the reaction rate of microperoxidases with peroxide is significantly smaller than that of the enzymes, the efficiency in the one-electron oxidation of phenolic substrates is almost comparable. Interestingly, the oxyferryl form of the triply positively charged microperoxidases shows a reactivity larger than that exhibited by horseradish peroxidase.
Dallacosta
Corrado
C
Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy.
Casella
Luigi
L
Monzani
Enrico
E
D000818:Animals; D002384:Catalysis; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D004579:Electron Transport; D006321:Heart / Q000502:physiology; D006418:Heme / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism; D006736:Horses; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010544:Peroxidases / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000737:chemistry; D013379:Substrate Specificity
D003574:Cytochrome c Group; D010446:Peptide Fragments; D010636:Phenols; D006418:Heme; D006861:Hydrogen Peroxide; D007501:Iron; D006735:Horseradish Peroxidase; D010544:Peroxidases; C021799:microperoxidase