C. Giulivi et E. Cadenas, THE REACTION OF ASCORBIC-ACID WITH DIFFERENT HEME IRON REDOX STATES OF MYOGLOBIN - ANTIOXIDANT AND PROOXIDANT ASPECTS, FEBS letters, 332(3), 1993, pp. 287-290
The interaction of ascorbate with different heme iron redox states of
myoglobin (ferrylmyoglobin, Fe(IV)=O; metmyoglobin, Fe(III); and oxymy
oglobin, Fe(II)O2) was examined by e.s.r. and absorption spectroscopy.
The reaction of ascorbate with ferryl- or met-myoglobin resulted in a
scorbyl radical production. The interaction of ascorbate with oxymyogl
obin proceeded with formation of ascorbyl radical, hydrogen peroxide,
and an overall oxidation of oxymyoglobin to metmyoglobin. The latter r
eaction proceeded via an oxoferryl complex intermediate - correspondin
g to ferrylmyoglobin and identified by treatment of the reaction mixtu
re with Na2S. These observations are consistent with a concerted elect
ron transfer mechanism, whereby the two electrons required for the red
uction of oxygen to hydrogen peroxide are donated by ascorbic acid and
the heme iron. The antioxidant and prooxidant aspects of these redox
transitions are discussed in terms of their kinetic properties.