Related Experiment Video
Updated: Jul 17, 2026

Light-driven Enzymatic Decarboxylation
Published on: May 22, 2016
Influence of major structural features of tocopherols and tocotrienols on their omega-oxidation by
Timothy J Sontag1, Robert S Parker
1Division of Nutritional Sciences, Cornell University, Ithaca, NY 14850, USA.
Abstract:
Human cytochrome P450 4F2 (CYP4F2) catalyzes the initial omega-hydroxylation reaction in the metabolism of tocopherols and tocotrienols to carboxychromanols and is, to date, the only enzyme shown to metabolize vitamin E. The objective of this study was to characterize this activity, particularly the influence of key features of tocochromanol substrate structure. The influence of the number and positions of methyl groups on the chromanol ring, and of stereochemistry and saturation of the side chain, were explored using HepG2 cultures and microsomal reaction systems. Human liver microsomes and microsomes selectively expressing recombinant human CYP4F2 exhibited substrate activity patterns similar to those of HepG2 cells. Although activity was strongly associated with substrate accumulation by cells or microsomes, substantial differences in specific activities between substrates remained under conditions of similar microsomal membrane substrate concentration. Methylation at C5 of the chromanol ring was associated with markedly low activity. Tocotrienols exhibited much higher Vmax values than their tocopherol counterparts. Side chain stereochemistry had no effect on omega-hydroxylation of alpha-tocopherol (alpha-TOH) by any system. Kinetic analysis of microsomal CYP4F2 activity revealed Michaelis-Menten kinetics for alpha-TOH but allosteric cooperativity for other vitamers, especially tocotrienols. Additionally, alpha-TOH was a positive effector of omega-hydroxylation of other vitamers. These results indicate that CYP4F2-mediated tocopherol-omega-hydroxylation is a central feature underlying the different biological half-lives, and therefore biopotencies, of the tocopherols and tocotrienols.
Related Concept Videos
Radical Autoxidation
Oxidation of Phenols to Quinones
o-hydroxy phenols are oxidized to o-quinones and p-hydroxy phenols to p-quinones. Such redox reactions involve the transfer of two electrons and two protons. The reversible redox property is crucial in...
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Oxidative Cleavage of Alkenes: Ozonolysis
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Phase I Oxidative Reactions: Overview

