FORMATION OF AGE PIGMENT-LIKE FLUORESCENT SUBSTANCES DURING PEROXIDATION OF LIPIDS IN MODEL MEMBRANES

Abstract

Formation of age pigment-like fluorescent substances during the lipid peroxidation of model membranes was studied. Fe2+- and ascorbate-induced lipid peroxidation of liposomal membranes containing phosphatidylethanolamine led to the formation of fluorescent substances which have characteristics similar to those of compounds derived from the reaction of phosphatidylethanolamine with purified fatty acid hydroperoxides. The fluorescent substances were accumulated in liposomal membranes; thiobarbituric acid-reactive substances formed during lipid preoxidation were immediately released from the liposomal membranes. The thiobarbituric acid-reactive substances free from the membranes were not reactive with amino compounds such as phosphatidylethanolamine in liposomes or glycine in aqueous phase. Products reacting with amino compounds are short-lived, and may be rapidly inactivated after released into aqueous phase. The formation of fluorescent products was inefficient when phosphatidylethanolamine incorporated into the liposome insensitive to lipid peroxidation was incubated with Fe2+ and ascorbate in the presence of liposomes sensitive to the peroxidation. Some product generated from peroxidation-sensitive lipids may react with the amino group of phosphatidylethanolamine molecules which are located on the same membranes, forming fluorescent substances. The presence of phosphatidylethanolamine in the membrane suppressed the formation of thiobarbituric acid-reactive substances, suggesting that phosphatidylethanolamine may react with radicals formed and terminate the propagation.