title: Magnetic spin effects in enzymatic reactions: radical oxidation of NADH by horseradish peroxidase.
abstract: A description of the elementary steps of the horseradish peroxidase (HRP)-catalyzed oxidation of NADH is presented, along with a quantitative analysis of the magnetic-field dependence of the enzymatic reaction. In the absence of H(2)O(2), the catalytic cycle begins with single-electron transfer from NADH to native HRP to form the NADH(.+) radical cation and the ferroperoxidase intermediate (Per(2+)). The theoretical framework for the magnetic-field dependent recombination of radical pairs has been extended to describe the magnetic-field dependence of reaction rate constants for multi-spin paramagnetic pairs, including the NADH(.+) radical cation and Per(2+) that exist in a correlated quartet electronic spin state. Good agreement between the experimentally observed and the theoretically calculated magnetic-field dependences of the effective rate constants underlines the importance of the initial single-electron-transfer step and supports a model in which the catalytic cycle begins with the one-electron reduction of HRP by NADH.
authors.affiliation: Institute of Chemical Kinetics and Combustion, Novosibirsk-90, 630090 Russia.
authors.forename: Maria S
authors.initials: MS
authors.lastname: Afanasyeva
authors.forename: Marc B
authors.initials: MB
authors.lastname: Taraban
authors.forename: Peter A
authors.initials: PA
authors.lastname: Purtov
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Leshina
authors.forename: Charles B
authors.initials: CB
authors.lastname: Grissom
mesh_terms: D002384:Catalysis; D004789:Enzyme Activation; D005609:Free Radicals / Q000138:chemical synthesis / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000737:chemistry*; D007700:Kinetics; D008280:Magnetics; D008956:Models, Chemical; D009243:NAD / Q000737:chemistry*; D010084:Oxidation-Reduction; D013997:Time Factors
chemical_list: D005609:Free Radicals; D009243:NAD; D006735:Horseradish Peroxidase