Autoxidation as a cause of altered lipid distribution in extracts from human red cells.

A characteristic alteration in the distribution of human red cell phospholipids represents an artifact due to autoxidation of the lipid extract. This alteration is manifested on silicic acid chromatography by a decrease mainly in the phosphatidyl ethanolamine and phosphatidyl serine fractions (probably because of their abundance of highly unsaturated fatty acids) and an increase in the phospholipid recovered with the more polar fractions, sphingomyelin and lysolecithin. No evidence was found for "lysocephalin" formation or plasmalogen breakdown in dry lipid extracts after autoxidation by exposure to air at room temperature for 24-35 hr. On thin-layer chromatography, however, the ninhydrin-positive streaking in the autoxidized samples may be erroneously attributed to the presence of "lyso" derivatives. When the alterations in lipid distribution described above are found, the possibility of this artifact should be considered.