tocopherol biosynthesis UPa:UPA00160 vitamin E biosynthesis pathway Biosynthesis of tocopherol, or vitamin E, a fat-soluble vitamin that is an important antioxidant. Natural vitamin E exists in eight different forms or isomers, four tocopherols and four tocotrienols. All isomers have a chromanol ring, with a hydroxyl group which can donate a hydrogen atom to reduce free radicals and a hydrophobic side chain which allows for penetration into biological membranes. There is an alpha, beta, gamma and delta form of both the tocopherols and tocotrienols, determined by the number of methyl groups on the chromanol ring. Each form has its own biological activity. Alpha-tocopherol is the most active form of vitamin E (tocopherol) in humans and is a powerful biological antioxidant. GO:0010189 cofactor biosynthesis