Retinol, All trans

Park, S.-M. 1978. Electrochemical studies of P-carotene, all-trans-retinal and all-trans-retinol in tetrahydro-furan. J. Electrochem. Soc. 125 216-222. 

Moreover, efficient rhodopsin regeneration may precede enzymatic reduction of all-fran.v-retinal to all-trans-retinol in the aged retina (Figure 15.2c) (Schadel et al., 2003). Upon rhodopsin regeneration, all-trans-retinal is released from the exit site of the protein into the lipid membrane (Figure 15.2c) (Schadel et al., 2003). From here the removal of all-tnms-retinal to the outer leaflet of the disc membrane is dependent on activity of ATP-binding cassette trasporter A4 (ABCA4) present in the rim of photoreceptor disc, known also as ABCR protein. 

Rutten, A. A., Wilmer, J. W., and Beems, R. B. (1988a). Effects of all-trans retinol and cigarette smoke condensate on hamster tracheal epithelium in organ culture. I. A cell proliferation study. Virchows Arch. B Cell Pathol. Inch Mol. Pathol. 55,167-175. 

Swatschek, D., Schatton, W., Muller, W. E. G., and Kreuter, J. (2002). Microparticles derived from marine sponge collagen (SCMPs) Preparation, characterization and suitability for dermal delivery of all-trans retinol. Eur. ]. Pharm. Biopharm. 54,125-133. 

Figure 15 Hydrogenation of all-trans-retinal to all-trans-retinol.

Sauer, J.-M. Sipes, I.G. (1995) Modulation of chemical-induced lung and liver toxicity by all-trans-retinol in the male Sprague-Dawley rat. Toxicology, 105, 237-249... 

The parent vitamin A compound, retinol, has the empirical formula C2oH3oO and a molecular weight (MW) of 286.44. The molecule comprises a cyclohexenyl (/3-ionone) ring attached at the carbon-6 (C-6) position to a polyene side chain whose four double bonds give rise to cis-trans (geometric) isomerism. The predominant isomer, all-trans-retinol (Fig. 1), possesses maximal (100%) vitamin A activity and is frequently accompanied in natural foodstuffs by smaller amounts of 13-ds-retinol, which exhibits 75% relative activity in the rat (6). Other cis isomers of retinol also occur in nature, but they are of low potency, and their contribution to the total vita-... 

For many applications, fluorescence detection offers no real advantages over absorbance detection, and the linear response range is more limited. Moreover, the fluorescence response of 13-d.v-retinol is less than that of all-trans-retinol, the relative fluorescence depending upon the solvent (133,134). 

Reversed-phase chromatography using semiaqueous mobile phases can separate all-trans-retinol from 13-cis-retinol, albeit rather poorly. Further separation of the minor cis isomers is not... 

Over the years, the form shown in frame A has been loosely defined as all-trans retinol. 

FIGURE 29.4 Chemical structure of vitamin A (all-trans retinol, (a//- )-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2,4,6,8-nonatetraen-l-ol). 

Vitamin A is a fat-soluble vitamin involved in critical biological functions, such as embryonic development, growth and vision. It has three primary forms retinol, retinal and retinoic acid. In addition, (3-carotene can be converted to some extent in the body into retinol and is therefore called provitamin A. The bioactivity of these vitamin A compounds varies considerably, ranging from 100% for all-trans retinol, 75% for 13-eis retinol and to just 17% for (3-carotene. All-trans retinol is the major form of vitamin A in milk fat, with values ranging from 8.0 to 12.0 pg/g fat in samples of commercial butter. In contrast, 13-cA retinol is present at a very low... 

The vitamin A content of foods is often given in terms of the international unit (IU). One IU of vitamin A is defined as 0.3 tg of all-trans-retinol. The term retinol equivalent (RE) is used to convert all sources of vitamin A and carotenoids in the diet to a single unit. One RE is by definition 1 pg of all-trans retinol, 12 pg of P-carotene, or 24 pg of other (mixed) provitamin A carotenoids. The recommended dietary allowance for vitamin A ranges from 375 pg RE/day for infants to 1,000 RE/day for adults. 

Electronic Absorption Spectroscopy. The absorption spectra of some polyenes in the crystalline state have been studied. On adsorption of certain gases on the crystallite surfaces, a new band appears on the low-energy side of the long-wavelength band in the spectra of these polyenes, e.g. at 536, 537, and 375 nm for all- trans-ft-carotene, 15-cis-/3-carotene, and retinyl compounds, respectively.92 The surface pressure vs. area isotherms and absorption spectra of all-trans-, 9-cis-, and 13-cis-retinal, all-trans-retinol, and all- trans-retinyl acetate have been studied at air-water and air-solid interfaces, respectively. The spectra of monolayers of the isomeric retinals showed a red shift of 15 lnm compared with the solution spectra, whereas... 

Retinol. The extensively investigated retinol molecule offers a relatively simple photophysical system due to the absence of a low-lying (n, tt ) state. Two main patterns characterize the fluorescence of all-trans retinol at 295°K (1) the break-... 

T, y-T, a-T, p-cryptoxanthin, lycopene, a-carotene, p-carotene, all trans retinol, 5-T3, y-T3, a-T3, lutein, zeaxanthin (27 min)... 

A microsomal retinol dehydrogenase catalyzes the oxidation of CRBP-hound all-trans-retinol to retinaldehyde it also acts as a 3a-hydroxysteroid dehydrogenase. A similar enzyme catalyzes the oxidation of 9-cis- and 11-ds-retinol, but not all-trans-retinol again, it has 3a-hydroxysteroid dehydrogenase activity. In the eye, the major product of this enzyme is 11-cts-retinaldehyde, whereas in other tissues it is 9-cts-retinaldehyde, which is then oxidized to 9-cis-retinoic acid (Section 2.3.2.1 Chen et al., 2000 Duester, 2000, 2001 Gamble et al., 2000 NapoU, 2001). Although there is known to be an isomerase in the eye for the formation of 11-cts-retinaldehyde as a... 

Anhydroretinol may arise by nonenzymic isomerization of all-trans-retinol under acidic conditions and can act as a precursor for the synthesis of other biologically active retroretinoids (McBee et al., 2000). 

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... 

Vogel S, Mendelsohn CL, Mertz JR, Piantedosi R, Waldburger C, Gottesman ME, and BlanerWS (2001) Characterization ofa new member of the fatty acid-binding protein family that binds all-trans-retinol. Journal of Biological Chemistry 276, 1353-60. 

Cis-retinol has 75% of the biological activity of all-tra/rs-retinol, and reti-naldehyde has 90%. Food composition tables give total preformed vitamin A as the sum of all-trans-retinol + 0.75 x 13-cis-retinol -I- 0.9 x retinaldehyde (Holland et al., 1991). 

The pigment epithelium of the retina receives all- trans-retinol from plasma RBP. It is then isomerized to 11-c/s-retinol, which may either be stored as... 

Polyenes exhibit two strong Raman bands between 1600 and 1500 cm and between 1200 and 1100 cm , respectively. These are attributed to in-phase vibrations of the C=C and C-C bonds, respectively, throughout the entire chain. Examples include all-trans-retinol (Fig. 4.1-6B), /3-carotene, and carotene-containing proteins, obtained, for instance, from lobster shells (Rimai et al., 1973 Oseroff and Callender, 1974). Polyene sequences with approximately twenty conjugated double bonds, formed by HCl elimination from polyvinyl chloride as a result of aging, also show these Raman bands at 1495 and 1115 cm (Peitscher and Holtrup, 1975). These bands are enhanced as a consequence of the resonance Raman effect, which makes it possible to detect such groups in polymers and natural materials, even at low concentration. 

Most current interest in u.v. spectra is concerned with retinal and its cis-trans isomers. Studies at 77 K include theoretical calculations, fluorescence, and the effect of protonation on the corresponding Schiff base. The singlet-triplet absorption spectrum of all-trans-retinol has been measured. Calculations on the absorption-emission spectra of rhodopsin suggest that there is little dependence on the angular twist in the polyene chain. Pulse radiolysis has made it... 

Tesoriere, L., DArpa, D., Re, R., and Livrea, M. A. (1997) Antioxidant reactions of all-trans retinol in phospholipid bilayers effect of oxygen partial pressure, radical fluxes, and retinol concentration. Arch Biochem Biophys 343, 13-8. 

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