JBC, Vol. 254, Issue 11, 4532-4535, Jun, 1979
Subunit inequivalence in superoxide anion formation during photooxidation of human oxyhemoglobin
L. S. Demma and J. M. Salhany
Subunit inequivalence in the photooxidation of human oxyhemoglobin was
investigated by quantitative analysis of the fraction of alpha and beta
chains oxidized after low intensity flash photolysis using white light in
quartz cuvettes. This reaction was previously shown to generate
methemoglobin and superoxide anion as photoproducts (Demma, L.S., and
Salhany, J.M. (1977) J. Biol. Chem. 252, 1226-1230). The present results
indicate that superoxide anion photodissociates from the alpha chain about
3 to 4 times more extensively than from beta. This difference was observed
in the presence of superoxide dismutase and catalase at both pH 7 and 9,
suggesting that photolysis is directly responsible. The reaction of
superoxide anion with oxyhemoglobin was also studied with the same
analytical methods and no chain differences could be observed. If the
electronic structure of the oxyheme complex is viewed as a spin equilibrium
between a singlet ground state and a charge transfer configuration, our
results may indicate that the uv component of white light perturbs this
equilibrium to a greater extent in the oxygenated alpha chain, implying
that the separation of energy levels may be smaller in that chain as
compared with beta.
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