In the vitamin E group, a-tocopherol is generally considered to be the most potent antioxidant with the highest vitamin bioactivity, yet y-tocopherol is produced in greater amounts by many plants and Is the principal tocopherol in the United States diet. This report describes a fundamental difference in the chemical reactivities of a-tocopherol and y-tocopherol with nitrogen dioxide (NO2), which leads to the formation of a nitrosating agent from a-tocopherol, but not from y-tocopherol. Nitric oxide (NO) is a major product of the reaction of --tocopherol with NO2, while a-tocopherol reacts with NO2 to form an intermediate tocopheroxide analogue. The biological sgnificance of y-tocopherol is s d by m epidemiological data as well as the observation that it is a more potent inhibitor than a-tocopherol of neoplastic transformation during the postinitiation phase in 3-methylcholanthrenetreated C3H/10T½ murine fibroblasts. This latter property suggests the superiority of y-tocopherol in a mammalian biologcal assay and a role for endogenous NO production in promotion of neoplasic ransformation.

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