Effects of the Tocopherols and Their Phosphates on Enzyme Systems

Abstract

Vitamin E, or more specifically a-, @-, y-, and &tocopherols, functions in the body in some manner which is still unknown. The current working hypothesis is that vitamin E acts primarily and specifically through some enzyme system and, secondarily, in a non-specific manner as a physiological antioxidant. The general methods for approaching this problem fall logically into three main divisions: first, are the studies of the changes in enzyme systems which result from vitamin E deficiency; second, and very closely allied, are studies of changes in enzyme systems in which the tocopherols

Reactions of Vitamin E with Peroxides. II. Reaction of Benzoyl Peroxide with d-α-Tocopherol in Alcohols*

“…In vivo oxidation of atocopherol in the presence of biochemical nucleophilic groups such as sulfhydryl or hydroxy groups should yield compounds analogous to the alkoxy-a-tocopherones. a-Tocopherone-forming reactions may be involved in the apparent protection by -tocopherol of enzyme sulfhydryl sites (Ames and Risley, 1949;Corwin and Schwarz, 1963). Moreover, the oxidation to an atocopherone followed by reduction to a-tocopherol provides a reasonable cyclic mechanism for inhibition of in vivo accumulation of peroxides whether by decomposition of peroxides or by interference with oxidation by free radical chain processes.…”

Vitamin E: Interactions with Free Radicals and Ascorbate

“…This reaction probably has biological significance since oxidation of tocopherol in systems containing nucleophilic sulfhydryl or hydroxy groups should yield tocopherone derivatives (24). In fact, such reactions have been indicated to be involved in the protection of essential sulfhydryl groups in enzymes by a-tocopherol (2,14).…”

Modulation of Phosphorylation of Tocopherol and Phosphatidylinositol by hTAP1/SEC14L2-Mediated Lipid Exchange

“…However, although regulatory effects of tocopheryl phosphate esters on enzymes have been reported early on [8], the in vivo biological function of αTP is not clear to date. αTP may act as an active cofactor for specific enzymatic reactions (reviewed in [9]), it may be a ligand of a receptor or transcription factor, or act as “second messenger” in the membrane capable of exerting regulatory effects [2].…”

“…The negative charge of αTP renders it more similar to phosphorylated messenger lipids such as phosphatidylinositol phosphates, with possibly increased ability to modulate specific and non-specific protein-membrane interactions (reviewed in [7] ). However, although regulatory effects of tocopheryl phosphate esters on enzymes have been reported early on [8] , the in vivo biological function of αTP is not clear to date. αTP may act as an active cofactor for specific enzymatic reactions (reviewed in [9] ), it may be a ligand of a receptor or transcription factor, or act as “second messenger” in the membrane capable of exerting regulatory effects [2] .…”