title: Kinetic characterization of the oxidation of carbidopa and benserazide by tyrosinase and peroxidase.
abstract: Carbidopa and benserazide have been described as inhibitors of dopa decarboxylase and both have been used in the treatment of Parkinson's disease. Because of their chemical structure as polyphenols, these compounds can behave as substrates of tyrosinase and peroxidase. We demonstrate that these enzymes oxidize both substrates. Since o-quinones are unstable, a chronometric method for enzymatic initial rate determinations was used based on measurements of the lag period in the presence of micromolar concentrations of ascorbic acid to kinetically characterize these substrates. In the case of tyrosinase, the values of the Michaelis constant for both substrates were greater than those described for dopa, although the catalytic constants were lower, probably due to the greater size of the substitute group in carbon 1. As regards peroxidase, the saturation of the enzyme by both substrates is possible, however this effect does not occur with the isomers of dopa. The distance of the charges from the benzene ring may enable the ring to approach the iron of the active site and, therefore, act.
authors.affiliation: GENZ: Investigation Group of Enzymology, Department of Biochemistry and Molecular Biology A, Faculty of Biology, University of Murcia, Espinardo, Murcia, Spain.
authors.forename: Joseph Louis
authors.initials: JL
authors.lastname: Munoz-Munoz
authors.forename: Francis
authors.initials: F
authors.lastname: Garcia-Molina
authors.forename: Mary
authors.initials: M
authors.lastname: Garcia-Molina
authors.forename: Joseph
authors.initials: J
authors.lastname: Tudela
authors.forename: Francis
authors.initials: F
authors.lastname: García-Cánovas
authors.forename: Joseph Neptune
authors.initials: JN
authors.lastname: Rodriguez-Lopez
mesh_terms: D001545:Benserazide / Q000378:metabolism*; D002230:Carbidopa / Q000378:metabolism*; D007700:Kinetics; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001545:Benserazide; D010544:Peroxidases; D014442:Monophenol Monooxygenase; D002230:Carbidopa