Polarographic studies on oxygen transport by human hemoglobin in buffer solutions.
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概要
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Oxygen transport by human hemoglobin (Hb) to an electrode surface with hypo-oxygen partial pressure has been studied by the polarographic technique. The oxygen reduction current in Hb solution open to the atmosphere increased linearly with Hb concentration up to <I>ca.</I> 2 mM (1 M=1 mol dm<SUP>−3</SUP>) heme. The current was ascribed to free and Hb bound oxygen. The increase in current with Hb concentration was attributed to the increasing oxygen supply to the electrode from oxygen bound Hb (oxyhemoglobin;oxyHb). Changes in temperature and pH largely affected the current, corresponding to the change in dissociation rate of oxygen from oxyHb. The relation between the current due to oxyHb and the apparent first order rate constant of the dissociation (<I>k</I>) measured by the stopped-flow method implies two different rate-determining steps of oxygen transport by Hb. When <I>k</I> exceeded <I>ca.</I> 60 s<SUP>−1</SUP>, the limiting step altered from the dissociation of oxygen to the diffusion of Hb molecules. It is concluded that the oxygen transport by Hb on physiological conditions is controlled by the diffusion of Hb. The diffusion coefficient of Hb in 20 mM heme as found in erythrocytes was estimated to be 5.8×10<SUP>−8</SUP>cm<SUP>2</SUP> s<SUP>−1</SUP> at 25 °C and pH 7.4.
- 公益社団法人 日本化学会の論文
著者
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Takagi Masanosuke
Department o f Agricultural Chemistry, College o f Agriculture, University
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Hayashi Katsumi
Department of Agricultural Chemistry, College of Agriculture, University of Osaka Prefecture
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