title: [Noncompetitive activation of peroxidase oxidation of o-phenylenediamine by melamine].
abstract: Peroxidase-catalyzed oxidation of o-phenylenediamine (PDA) is greatly activated with melamine (MA) in 15 mM phosphate-citrate buffer at pH 6.0-7.4 in a noncompetitive manner: kcat and Km increase in direct proportion to the MA concentration. An extent of the activation is quantitatively characterized with a coefficient alpha (in M-1), which essentially increases along with the rise in pH from 6.0 to 7.4. MA acts as a nucleophilic catalyst in the oxidation process: it most likely affects the peroxidase active site from the distal position of heme. MA non-competitively inhibits the peroxidase oxidation of PDA at pH 4.3, since it completely loses its nucleophilic properties in acidic medium. A rapid, highly accurate, and simple analytical test system based on the kinetics of melamine-activated oxidation of PDA is proposed for the quantitative determination of melamine within the concentration range of 10(-4)-10(-3) M. This test system uses the spectrophotometric determination of the PDA oxidation product at 455 nm.
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, ul. Kuprevicha 5/2, Minsk, 220141 Belarus.
authors.forename: E I
authors.initials: EI
authors.lastname: Karaseva
authors.forename: I V
authors.initials: IV
authors.lastname: Naumchik
authors.forename: D I
authors.initials: DI
authors.lastname: Metelitsa
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D010655:Phenylenediamines / Q000378:metabolism*; D014227:Triazines / Q000378:metabolism*
chemical_list: D010655:Phenylenediamines; D014227:Triazines; C034193:1,2-diaminobenzene; D010544:Peroxidases; C011907:melamine