Peroxidase catalyzed oxidation of capsaicinoids steady state and transient state kinetic studies英文电子书.pdf

ABB Archives of Biochemistry and Biophysics 417 (2003) 18–26 /locate/yabbi Peroxidase-catalyzed oxidation of capsaicinoids: steady-state and transient-state kinetic studies Douglas C. Goodwin* and Kristen M. Hertwig Department of Chemistry and Program in Cell and Molecular Biosciences, Auburn University, Auburn, AL 36849-5312, USA Received 12 May 2003, and in revised form 17 June 2003 Abstract Capsaicinoids are the pungent compounds in Capsicum fruits (i.e., ‘‘hot’’ peppers). Peroxidases catalyze capsaicinoid oxidation and may play a central role in their metabolism. However, key kinetic aspects of peroxidase-catalyzed capsaicinoid oxidation remain unresolved. Using transient-state methods, we evaluated horseradish peroxidase compound I and II reduction by two prominent capsaicinoids (25 C, pH 7.0). We determined rate constants approaching 2 107 5 1 1 and 5 10 M s for compound I and com- pound II reduction, respectively. We also determined kapp values for steady-state capsaicinoid oxidation approaching 8 105 M1 s1 (25 C, pH 7.0). Accounting for stoichiometry, these are in excellent agreement with constants for compound II reduction, suggesting that this reaction governs capsaicinoid-dependent peroxidase turnover. Ascorbate rapidly reduced capsaici- noid radicals, assisting in the determination of the kinetic constants reported. Because ascorbate accumulates in Capsicum fruits, it