11-c/s retinol

Q s-retinol has 75% of the biological activity of aU-trans-retinol, and reti-naldehyde has 90%. Food composition tables give total preformed vitamin A as the sum of aU-trans-retinol -i- 0.75 x 13-c/s-retinol - - 0.9 x retinaldehyde (Holland et al., 1991). 

RBP is relatively rich in aromatic amino acids, which create a deep hydrophobic pocket that is specific for the 8-ionone ring, polyene side chain, and polar end group. In addition to all- trans-retinol, RBP binds retinaldehyde, retinoic acid, and 13-c/s-retinol, but not retinyl esters or carotene. RBP shows considerable structural homology with 8-lactoglobulin from milk and other... 

The two cellular retinol binding proteins bind aH-trans- emd 13-c/s-retinol, but not 9-cis- or 11-ds-retinol, or retinoic acid. They also bind retineddehyde, although there is a distinct retinaldehyde binding protein in the eye ... 

Retinol, the parent molecule of the vitamin A family, is a fat-soluble lipid alcohol (C20H30O, molecular mass 286.4) composed of a methyl substituted cyclohexenyl (yS-ionone) ring, an 11-carbon conjugated tetraene side chain, and a terminal hydroxyl group (Figure lA, Ri). Most of the double bonds can exist in either trans or cis conformation. All-traws-retinol is the most stable and most prevalent form in foods and tissues, but small amounts of other geometric isomers such as 9-cis- and 13-c/s-retinol are found in some cells. The terminal hydroxyl group of retinol can be free or esterified with a... 

Fig. 13.7 Isomerization of 11-trans-retinol ester to the 11-c/s-retinol catalyzed by the isomero-hydrolase.

Besler et al. [671] studied retinal and retinol isomer retention on a silica column (A = 325nm or 371 nm) with hexane/MlBE (97/3 and 93/7), hexane/dioxane (93/7 and 94/6), and heptane/MrBE (94/6 and 93/7) mobile phases. The purpose of this work was to find an accq)table replacement for dioxane, namely, MrBE. The best overall chromatography resulted when 94/6 hexane/dioxane resolved 11,13-di-cis-, 13-CIS-, 9,11-13-tri-cis-, 9,13-di-cis-, 11-cis-, 7,1 l-di-c , 9-cis-, 7,9-di-cis, and all-tra s retinol in 15 min. Broader peaks but better resolution were obtained for the same solute set when 93/7 hexane/MtBE was used (elution was complete in 21 min), MlBE in hexane also gave excellent resolution of 13-c/s-retinoic acid and z -trans retinoic acid methyl esters on a silica column (A = 340 nm) in <5 min, whereas dichloromethane/hexane (35/65) required 17 min and toluene/hexane (45/55) required 10 min. It was found that for the toluene/hexane mobile phase, very small changes in the water content of the system dramatically and adversely affected the chromatography. The MrBE/hexane mobile phase provided more overall stability with respect to these changes. 

In three separation schemes, retinyl, retinal, and retinol palmitate isomos were analyzed [665]. A silica colunm was used for all separations. Seven retinal isomers (7-, 9-, 11-, n-cis, 7,9-, ll,13-di-c/s, and all-rnms) were eluted and baseline resolved in 18 min with a 97/3 -heptane/methyl /-butyl ether (A = 371nm) mobile phase. The seven retinol isomers (9-, 11-, 13-cis, 7,9-, 7,13-, 9,13-, 11,13-di-cis, 9,11,13-tri-cij, and all-/ru s) were incompletely resolved and eluted in 22 min using a 94/6 n-heptane/methyl /-butyl ether (2 = 325 nm) mobile phase. Finally, retinyl isomers (9-, 11-, 13-c , 7,9-9,13-di-c/y) were incompletely resolved in 5 min using a 99/1 n-heptane/methyl /-butyl ether (A = 325 nm) mobile phase. For this study 0.1 ng injections were made. 

Physical Methods.—Separation and Assay. A range of isomers of astaxanthin (8) diacetate (9-cis, 13-cis, 15-cis, 9,9 -di-cis, 9,13-di-cw, 9,13 -di-cw, 13,13 -di-cw, 13,15-di-cw), prepared by thermal and iodine-catalysed isomerization of irans-(S) have been separated by h.p.l.c.126 A procedure has been developed for separation of bean leaf etioplast pigments, including carotenoids,127 by h.p.l.c. H.p.l.c. separations of esters of all-trans-, 9-cis-, 11-cw-, and 13-cw-retinol,128-130 and determinations of retinol in serum,131 retinol and 13-cw-retinoic acid,132 and the aromatic retinoid (195)133 in plasma have been described. A reversed-phase ion-pair... 

Amhold T, Tzimas G, Wittfoht W, Plonait S, Nau H (1996) Identification of 9-d5-retinoic acid and 9,13-di-c/5-retinoic acid, and 14-hydroxy-4,14-retro-retinol in human plasma after liver consumption. Life Sci 59 PL169-PL177... 

---