Biphasic nature in the autoxidation reaction of human oxyhemoglobin |
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| Institution: | 1. Department of Physics and Astronomy, Lehman College, City University of New York, NY 10468, USA;2. Department of Physics, Graduate Center, City University of New York, NY 10016, USA;3. Department of Astrophysics, American Museum of Natural History, NY 10024, USA;4. Laboratoire de Physique Théorique et Hautes Énergies - LPTHE Sorbonne Université, CNRS, 4 Place Jussieu, 75005 Paris, France;5. Institute for Theoretical Physics, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium;6. Institute of Modern Physics, Northwest University, Xi''an 710069, China;7. NSFC-SPTP Peng Huanwu Center for Fundamental Theory, Xi''an 710127, China;8. Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi''an 710069, China;9. Max–Planck–Institut für Physik, Werner–Heisenberg–Institut, 80805 München, Germany;10. Arnold Sommerfeld Center for Theoretical Physics Ludwig-Maximilians-Universität München, 80333 München, Germany;11. Department of Physics, Northeastern University, Boston, MA 02115, USA;3. Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0600;4. Department of Physics, Emory University, Atlanta, Georgia 30322-2430;3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Aoba, Sendai 980-8577, Japan;4. Graduate School of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho, Nagoya 467-8603, Japan;5. Department of Biochemistry, Keio University School of Medicine, Shinano-machi, Shinjyuku, Tokyo 160-8582, Japan |
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| Abstract: | In comparison with myoglobin molecule as a reference, we have studied the autoxidation rate of human oxyhemoglobin (HbO2) as a function of its concentration in 0.1 M buffer at 35°C and in the presence of 1 mM EDTA. At pH 6.5, HbA showed a biphasic autoxidation reaction that can be described completely by a first-order rate equation containing two rate constants — kf, for fast autoxidation of the α-chain, and ks, for slow autoxidation of the β-chain, respectively. When tetrameric HbO2 was dissociated into αβ-dimers by dilution, the value of kf increased markedly to an extent comparable with the autoxidation rate of horse heart oxymyoglobin (MbO2). The rate constant ks, on the other hand, was found to remain at an almost constant value over the whole concentration range from 1.0 × 10?3 M to 3.2 × 10?6 M in heme. At pH 8.5 and pH 10.0, however, the autoxidation of HbO2 was monophasic, and no enhancement in the rate was observed by diluting hemoglobin solutions. Taking into consideration the effects of 2,3-diphosphoglyceric acid and chloride anion on the autoxidation rate of HbO2, we have characterized the differential susceptibility of the α- and β-chains to the autoxidation reaction in aqueous solution. |
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