REACTIVITY OF PHOTOCHEMICALLY‐GENERATED LIPID HYDROPEROXIDES IN CELL MEMBRANES WITH GLUTATHIONE PEROXIDASE

Abstract

The ability of glutathione peroxidase (Gpx) to catalyze the reductive inactivation of phot‐ochemically‐generated lipid hydroperoxides (LOOHs) was investigated, using hematoporphyrin derivative (HPD) as a photosensitizing agent and erythrocyte ghosts as membrane targets. Glutathione peroxidase was reactive toward photoperoxidized membranes only after their exposure to phospholi‐pase A₂ (PLA₂)‐ Iodometrically‐determined LOOH values were typically 30–40% greater than values measured by enzymatic assay using Gpx and glutathione reductase. A consistent result was obtained when photooxidized membranes were treated with PLA₂ and GSH/Gpx followed by iodometric assay, viz. persistence of approximately 40% of the starting LOOH. Whereas photooxidized egg phosphatidylcholine liposomes underwent total LOOH loss when incubated with PLA₂ and GSH/Gpx, no net loss was observed with photooxidized cholesterol/dimyristoyl‐phosphatidylcholine liposomes. The results suggest that cholesterol hydroperoxides in ghost membranes account for the Gpx‐resistant fraction of LOOHs.