All-frans-retinol

Retinol and its esters exhibit similar UV absorption spectra within a broad wavelength range and have practically equal molar absorptivities when dissolved in a given solvent. The e value of crystalline all-frans-retinol in 2-propanol at the Amax of 325 nm is 52,300 (120), which corresponds to an A m of approximately 1830. The on-column minimum detectable quantity of vitamin A using UV absorption is approximately 2 ng (121). 

Cheese Saponify (ambient), extract unsaponifiables with hexane. LiChrosorb Si-60 5 pm 250 X 4 mm Hexane /methyl ethyl ketone, 90 10 Carotene, all-frans-retinol Vis 450 nm (carotene) UV 340 nm (retinol) 146... 

The lipase-catalysed hydrolysis of methyl 2-fluoro-2-arylpropionates was proposed to proceed via a mechanism whereby, after ester hydrolysis, the enzyme facilitates the elimination of fluoride ion with the formation of a carbocation stabilized by the adjacent C02 group.230 Determination of the crystal structure of human sialidase Neu2, an enzyme that catalyses the hydrolysis of sialic acids, reveals a tyrosine residue that is positioned in the active site to stabilize the carbocation proposed as an intermediate in the hydrolysis.231 ll-Fluoro-all-frans-retinol is found to undergo isomerization to its 11 -cis form in the presence of visual cycle enzymes, in contrast to a previous study where no isomerization was reported.232 The result of the prior study was taken as evidence for a carbonium ion pathway in the isomerization. Although the authors of the present study do not rule out such a mechanism, they suggest that the isomerization mechanism remains unknown. Data obtained in a study of the oxidation of... 

Chen H, Howald WN, and Juchau MR (2000) Biosynthesis of all-frans-retinoic acid from all-OB/ix-retinol catalysis of all-frans-retinol oxidation by human P-450 cytochromes. Drug Metabolism and Disposal 28,315-22. 

Vogel S, Mendelsohn CL, Mertz JR, Piantedosi R, Waldburger C, Gottesman ME, and Blaner WS (2001) Characterization of a newmember of the fatty acid-binding protein family that binds all-frans-retinol. Journal of Biological Chemistry 276,1353-60. 

Cis-trans isomerisation may be a cause of loss of potency of a dmg if the two geometric isomers have different therapeutic activities. Vitamin A (all-frans-retinol) is enzymatically... 

Synonyms Retinol hexadecanoate all-frans-Retinol paimitate Source Catchpole, O. J. Grey, J. B. Noermark, K. A. J. Chem. Eng. Data (1998), 43(6), 1091-1095. 

Chen Y. Saari JC, Noy N. Interactions of all-frans-retinol and long-chain fatty acids with interphotoreceptor retinoid-binding protein. Biochemistry 1993 32 11,311-11,318. 

Figure 1 Chemical structure of (A) vitamin A, all-frans-retinol (B) /i-carotene (C) vitamin D, cholecalciferol (D) vitamin E, a-tocopherol and (E) vitamin Ki(20), phylloquinone.

Wald was also able to explain the sequence of events by which the rhodopsin molecules are regenerated. After dissociation of all-frans-retinal from the protein, the following enzyme-mediated changes occur. All-frans-retinal is reduced to the alcohol all-frans-retinol, also called all-frans-Vitamin A. 

Two methods were developed to stabilize retinol during GLC analysis, namely formation of the trimethylsilyl ethers (Vecchi et al., 1967, 1973) and formation of perhydro derivatives of retinol by catalytic hydrogenation (Fenton et al., 1973). Trimethylsilyl ethers of retinol were separated on columns of Chromosorb W-HP coated with 7% Silicone QF-1 and conditioned by repeated injections of V,0-bis(trimethylsilyl)acetamide. Some separation of isomers of retinol, i.e., all-rran5-retinol from 13-cw-retinol, was also possible. The retention times of various isomers, relative to the trimethylsilyl ether of all-fran -retinol (1.00), were 13-cw (0.64), 11,13-di-cw (0.28), and retro (0.72 and 1.00) (Vecchi etal., 1967). 

Waters ODS column (1.2 x 10 cm) at 2 mL/mm with a linear gradient of 15% water m methanol to methanol over 20 mm, followed by 30 mm of methanol. This water/methanol-based system resolves 5,6-epoxyretmol, all-fran -retinol, all-tran5-retmal, anhydroretmol, and the esters retmyl docosahexanoate, retinyl palmitoleate, retinyl linoleate, and retinyl stearate, whereas retinyl palmitate and retinyl oleate elute as a single peak (Fig. 2). 

The 9-cis and 13-cis isomers of retinaldehyde are often formed thermally in aqueous detergent solutions or dispersions of all-irons-retinaldehyde (Hubbard, 1956 Groenendijk et al., 1980 Futterman and Rollins, 1973). The presence of nucleophiles (FADH2, FMNH2), bacteria, and reducing conditions seems to be important for obtaining appreciable yields of 9-c/y-retinaldehyde (Futterman and Rollins, 1973 Rotmans et al., 1972). With respect to retinol, which is not acted upon by nucleophiles, our own observations show that in RPE homogenates, all-frans-retinol is partially isomerized to 13-ds-retinol (see Fig. 9). 

A slow appearance of labeled 11-c/s-retinyl palmitate in the RPE is demonstrable after injection of all-fran5-[ll,12- H]retinol directly into the eyes of dark-adapted frogs (Fong et al., 1983a). Initially, the all-frans-retinol is taken up by the RPE and converted to all-trans-retinyl palmitate. After several hours, the all-fra i-retinyl palmitate is found to have a fairly constant specific activity, as shown in Fig. 15. No labeled 1 l-cis isomer is detectable at first, but between 2 and 7 h, radioactivity starts appearing in the 11-cis-retinyl palmitate. After 15 h, however, Fig. 15 shows that its specific activity is still only 20% of that of the... 

In the plasma, vitamin A is transported from its major depots in the liver to tissues in several forms, primarily as a 1 1 molar complex of all-frans-retinol with RBP. Low concentrations of dll-trans- and 13-ds-retinoic acid, probably bound to albumin, and retinyl and retinoyl p-glucuronides, are also present. Holo-RBP also interacts strongly with transthyretin in the plasma. All of these forms of vitamin A can be taken up by various tissue cells. Several tissues besides the parenchymal cells of the liver can also synthesize RBP, as evidenced by the presence of mRNA for RBP within such cells. Thus, the extensive recycling of retinol between the liver and peripheral tissue cells may well occur as complexes with RBP. Another possibility is that retinyl ester, which is synthesized in essentially all cells of the body, might be carried back to the liver in lipoproteins. 

Li H, Tyndale ST, Heath DD, Letcher RJ. Determination of carotenoids and all-frans-retinol in fish eggs by liquid chromatography—electrospray ionization—tandem mass spectrometry. J Chromatogr B 2005 816 49—56. 

Apocarotenoids exhibit different biological functions. The most important apocarotenoid is vitamin Aj (all-frans-retinol). 

Figure 23.16 The Structures of Retinal and Rhodopsin. (a) All-frans-retinol (vitamin A)...

An important observation is that endogenous levels of retinoids in human embryos are quantitatively and qualitatively similar to those in Xenopus embryos, whereby the following retinoids were detected 13-cw-RA, 9-cis-RA, dill-trans-RA, all-fran -retinol, all-fran -dd-retinol and all-trans-retinal [8, 37, 39]. Until this report, dd-retinol had been detected only in chick embryos [33], but not in rodent embryos. These retinoids were detected in Xenopus embryos at levels that can be accurately quantified with a sensitive HPLC detection system. In contrast, levels of the same endogenous retinoids in rodents are low [19, 20, 21], resulting in less reliable quantification. 

Figure 4 Model of atRA biogeneration in mammals. REH, retinyl ester hydrolase (e.g., ES4 and ES10) TTR, transthyretin RAR-RXR, the heterodimer of retinoic acid receptors with retinoid X receptors atRCHO, all-frans-relinal atROH, all-frans-retinol CRBP(I), cellular retinol binding protein, type I LRAT, lecithin retinol acyltransferase SRBP, semm retinol binding protein. CRBP(I), CRABP(I), and CRABP(II) have been placed in the same cell for simplicity. This does not necessarily occur in vivo.

Figure 1 (A) Structure of all-frans-retinol and several related forms. (B) Beta-carotene (all-frans) showing the position of 15,15 double bond that through cleavage yields retinal, which can be reduced to form retinal, giving rise to all of the structures indicated in Figure 1A.

---