Abstract
Experiments were performed to delineate the biochemical mechanism of hemoglobin (Hb)-catalyzed lipid peroxidation in human red blood cells (RBCs). Using a modified Langmuir trough lipid monolayer technique, we found that oxidized Hb induced an increase in lipid monolayer surface pressure, suggesting that oxidized Hb readily releases its heme moiety into the lipid monolayer. To confirm our interpretation that oxidized Hb readily releases its heme moiety, we monitored the fluorescence of Hb tryptophan upon oxidation of Hb. We found an increase in Hb fluorescence in the aqueous phase of our monolayer system after the addition of H 2O 2. The increase in fluorescence should reflect the departure of heme from globin due to a decrease in fluorescent quenching effect by the heme moiety. The rate of increase in lipid monolayer surface pressure upon Hb oxidation differed from Hb to Hb with an order of Hb E > F > S > A. The ability of various Hbs to affect lipid peroxidation in the RBC membrane, as monitored by the parinaric acid oxidation technique, followed this same order. In addition, hemin was shown to be a more potent catalyst of lipid peroxidation in RBC membrane than nonheme irons.
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