Manganese(II) Catalyzes the Bicarbonate-Dependent Oxidation of Amino Acids by Hydrogen Peroxide and the Amino Acid-Facilitated Dismutation of Hydrogen Peroxide

• Published in: Proceedings of the National Academy of Sciences - PNAS 1990-01, Vol.87 (1), p.389-393
• Main Authors: Berlett, B. S., Chock, P. B., Yim, M. B., Stadtman, E. R.
• Format: Article
• Language: English
• Subjects: Alanine; Aldehydes; Amino Acids; Bicarbonates; Biochemistry; Biological and medical sciences; Carbonyl compounds; Cell metabolism, cell oxidation; Cell physiology; Free Radicals; Fundamental and applied biological sciences. Psychology; Gas mixtures; Hydrogen; Hydrogen Peroxide; Keto Acids; Kinetics; Leucine; Manganese; Models, Biological; Molecular and cellular biology; Oxidation; Oxidation-Reduction; Reagents; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.87.1.389

In bicarbonate/CO2buffer, Mn(II) and Fe(II) catalyze the oxidation of amino acids by H2O2and the dismutation of H2O2. As the Mn(II)/Fe(II) ratio is increased, the yield of carbonyl compounds per mole of leucine oxidized is essentially constant, but the ratio of α-ketoisocaproate to isovaleraldehyde formed increases, and the fraction of H2O2converted to O2increases. In the absence of Fe(II), the rate of Mn(II)-catalyzed leucine oxidation is directly proportional to the H2O2, Mn(II), and amino acid concentrations and is proportional to the square of the {HCO3}-concentration. The rate of Mn(II)-catalyzed O2production in the presence of 50 mM alanine or leucine is about 4-fold the rate observed in the absence of amino acids and accounts for about half of the H2O2consumed; the other half of the H2O2is consumed in the oxidation of the amino acids. In contrast, O2production is increased nearly 18-fold by the presence of α-methylalanine and accounts for about 90% of the H2O2consumed. The data are consistent with the view that H2O2decomposition is an inner sphere (cage-like) process catalyzed by a Mn coordination complex of the composition Mn(II), amino acid, {({HCO3}-)}2. Oxidation of the amino acid in this complex most likely proceeds by a free radical mechanism involving hydrogen abstraction from the α-carbon as a critical step. The results demonstrate that at physiological concentrations of {HCO3}-and CO2, Mn(II) is able to facilitate Fenton-type reactions.