A new vitamin E constituent having an unusual methylene unsaturation at the isoprenoid-chain terminus of alpha-tocopherol (alpha-Toc) was isolated from chum salmon eggs and was found to have identical antioxidant activity as does alpha-Toc in methanol or liposomal suspension at 37 degrees C. Here we report that this marine-derived tocopherol (MDT) is broadly distributed with alpha-Toc in the tissue of marine fish, and that the MDT composition of total vitamin E is greater in the flesh of cold-water salmon (12-20%) than in that of tropical fish (< or =2.5%). Vitamin E analysis of cultured masu salmon maintained on a MDT-deplete diet showed substantially less MDT content than native masu salmon, suggesting a trophic origin of MDT. This contention is supported by the finding of MDT in marine plankton from the cold waters of Hokkaido. We found that MDT inhibited peroxidation of cholesterol-containing phosphatidylcholine liposomes to a greater extent than did alpha-Toc at 0 degrees C. Furthermore, the ratios of the rate constants for MDT and alpha-Toc to scavenge peroxyl radicals increased with decreasing rates of radical flux in liposomes and fish oil at 0 degrees C, indicating that the enhanced activity of MDT at low temperature is attributed to its greater rate of diffusion in viscous lipids. These results suggest that MDT production, or its trophic accumulation, may reduce lipid peroxidation in marine organisms functionally adapted to cold-water environments.