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      https://www.ias.ac.in/article/fulltext/jbsc/016/01-02/0055-0070

    • Keywords

       

      Oxyhaemoglobin; methaemoglobin; autoxidation; superoxide; superoxide dismutase; catalase; erythrocytes; animals; phyla

    • Abstract

       

      Oxyhaemoglobins from erythrocytes of different animals including fish, amphibians, reptiles, birds, mammals and human beings have been isolated by ion-exchange chromatography over phosphocellulose and the comparative rates of autoxidation of oxyhaemoglobin studied. The mechanism of autoxidationin vitro has been elucidated using toad as well as human oxyhaemoglobin. Autoxidation is markedly inhibited by carbon monoxide as well as by anion ligands, namely, potassium cyanide, sodium azide and potassium thiocyanate. The inhibition by anions is in the same order as their strength as nucleophiles, indicating that it is the oxyhaemoglobin and not the ligand-bound deoxy species which undergoes autoxidation. The structure of oxyhaemoglobin is considered to be mainly $$Hb^{3 + } O_2^{ - \cdot } $$ and determination of the rate of autoxidation with or without using superoxide dismutase and catalase indicates that the initial process of autoxidation takes place by dissociation of $$Hb^{3 + } O_2^{ - \cdot } $$ to methaemoglobin and superoxide to the extent of 24%. The superoxide thus produced reattacks oxyhaemoglobin to produce further methaemoglobin and hydrogen peroxide. H2O2 is a major oxidant of oxyhaemoglobin producing methaemoglobin to the extent of 53%. A tentative mechanism of autoxidation showing the sequence of reactions involving superoxide, H2O2 and OH has been presented.

    • Author Affiliations

       

      Asoke Mal1 I B Chatterjee1

      1. Department of Biochemistry, University College of Science, 35, Ballygunge Circular Road, Calcutta - 700 019, India
    • Dates

       
  • Journal of Biosciences | News

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