|
|Section2= |Section6= |Section7= }} α-Tocopherol is a type of tocopherol or vitamin E. It has E number "E307". α-Tocopherol is a form of vitamin E that is preferentially absorbed and accumulated in humans. The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of spontaneous abortions in pregnant rats relative to alpha-tocopherol. There are three stereocenters in alpha-tocopherol, so this is a chiral molecule. The eight stereoisomers of alpha-tocopherol differ in the arrangement of groups around these stereocenters. In the image of ''RRR''-alpha-tocopherol, all three stereocenters are in the ''R'' form. However, if the middle of the three stereocenters were changed (so the hydrogen was now pointing down and the methyl group pointing up), this would become the structure of ''RSR''-alpha-tocopherol. ''RSR''-alpha-tocopherol and ''RRR''-alpha-tocopherol are diastereomers of each other. These stereoisomers can also be named in an alternative older nomenclature, where the stereocenters are either in the ''d'' or ''l'' form. 1 IU of tocopherol is defined as ⅔ milligrams of ''RRR''-alpha-tocopherol (formerly named d-alpha-tocopherol or sometimes ddd-alpha-tocopherol). 1 IU is also defined as 1 milligram of an equal mix of the eight stereoisomers, which is a racemic mixture called ''all-rac''-alpha-tocopheryl acetate. This mix of stereoisomers is often called dl-alpha-tocopheryl acetate, even though it is more precisely dl,dl,dl-alpha-tocopheryl acetate). However, 1 IU of this racemic mixture is not now considered equivalent to 1 IU of natural (RRR) α-tocopherol, and the Institute of Medicine and the USDA now convert IU's of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 "milligrams α-tocopherol".〔''(Composition of Foods Raw, Processed, Prepared USDA National Nutrient Database for Standard Reference, Release 20 )'' USDA, February 2008〕 ==References== de:Alpha-Tocopherol 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alpha-Tocopherol」の詳細全文を読む スポンサード リンク
|