Reactivity of photochemically-generated lipid hydroperoxides in cell membranes with glutathione peroxidase.
The ability of glutathione peroxidase (Gpx) to catalyze the reductive inactivation of photochemically-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 phospholipase 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.
Thomas
J P
JP
Girotti
A W
AW
D004910:Erythrocyte Membrane / Q000378:metabolism*; D005979:Glutathione Peroxidase / Q000378:metabolism*; D017324:Hematoporphyrin Derivative; D006415:Hematoporphyrins / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008054:Lipid Peroxides / Q000097:blood*; D008081:Liposomes; D008563:Membrane Lipids / Q000097:blood*; D010713:Phosphatidylcholines; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D006415:Hematoporphyrins; D008054:Lipid Peroxides; D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D011838:Radiation-Sensitizing Agents; D017324:Hematoporphyrin Derivative; D005979:Glutathione Peroxidase