Magnetic Spin Effects in Enzymatic Reactions:  Radical Oxidation of NADH by Horseradish Peroxidase

• Published in: Journal of the American Chemical Society Vol. 128; no. 26; pp. 8651 - 8658
• Main Authors: Afanasyeva, Maria S, Taraban, Marc B, Purtov, Peter A, Leshina, Tatyana V, Grissom, Charles B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 05.07.2006
• Subjects: Catalysis; Enzyme Activation; Free Radicals - chemical synthesis; Free Radicals - chemistry; Horseradish Peroxidase - chemistry; Kinetics; Magnetics; Models, Chemical; NAD - chemistry; Oxidation-Reduction; Time Factors
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0585735

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 H2O2, the catalytic cycle begins with single-electron transfer from NADH to native HRP to form the NADH•+ radical cation and the ferroperoxidase intermediate (Per2+). 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 Per2+ 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.