Chemical and Biological Studies Related to the Metabolic Function of Vitamin E

Abstract

Three dif'ferent phases of current research activities on the metabolic function of vitamin E are included in this report. These are: (1) the isolation and tentative characterization of a reversible oxidation product of tocopherol; (2) the effect of a-tocopheryl phosphate and other compounds of similar properties on the succinoxidase system; and (3) a re-evaluation of the biological activity of compounds related to vitamin E.Evidence for the existence of a reversible oxidation product of tocopherol was first obtained in this laboratory two years ago in spectrophotometric studies of the oxidation of a-tocopherol. In these experiments, tocopherol was oxidized by two equivalents of ferric iron in the presence of excess 2 , 2'bipyridine to react with the ferrous iron produced. When the oxidized tocopherol was reduced by ascorbic acid immediately following the completion of the oxidation, the product showed the same ultraviolet absorption curve as a-tocopherol. If the reduction was carried out a t subsequent intervals up to 20 hours, the presence of increasing amounts of the irreversible oxidation product, tocopheryl quinone, was evident. These observations suggested that the tocopherol was first converted to a primary oxidation product which could be readily reduced to the original tocopherol or converted irreversibly to the tocopheryl quinone. Experiments were then undertaken to find if such a product existed.Further experiments showed that by careful oxidation of the tocopherol a t -5"C., followed by extraction and chromatographic separation on alumina, the primary oxidation product could be obtained as a colorless oil. Elementary analyses of the product indicated that it has the composition CsaHsoOs. Thus it is isomeric with the tocopheryl quinone and differs from tocopherol only in the presence of an additional oxygen atom. The relationships existing between tocopherol and its oxidation products are summarized in FIGURE 1. a-Tocopherol may be converted by a reversible, bivalent oxidation to a primary oxidation product. The semiquinone radical of tocopherol' is probably an intermediate in the formation of the product. Upon exposure to very dilute acids, the primary oxidation product is converted irreversibly to tocopheryl quinone, the first oxidation product of tocopherol previously attainable? The tocopheryl quinone is reduced much less readily than the primary oxidation product, and the reduction gives rise to tocopheryl hydroquinone.2 Interest in the primary oxidation product was heighteneJ by the observation that it was biologically active. When fed orally, the product had 3$ of the activity of d,l-a-tocopherol, as measured by the conventional rat assay, When administered by intrsperitoneal injection as a suspen-A Reversible Oxidation Product of Tocopherol.

Theoretical frameworks of ethnic minority youth achievement.

“…The fifth theme of TDM is that the school should operate as a community. Schools that have a shared goal and communicate that all students are valued and belong in the classroom not only enhance the educational outcomes of its students (Lee & Smith, 1996) but also build the morale of the staff (Boyer, 1995). This collective approach to education makes students feel empowered to learn while simultaneously encouraging teachers and staff to feel vital to the child's learning.…”