Retinol biosynthesis

Biotin metabolism Folate biosynthesis One carbon pool by folate Retinol metabolism Porphyrin and chlorophyll metabolism Terpenoid biosynthesis Xenobiotics metabolism Ubiquinone biosynthesis Flavonoids, stilbene, and lignin biosynthesis... 

D2. De Luca, L., Rosso, G., and Wolf, G., The biosynthesis of a mannolipid that contains a polar metabolite of 15- C-retinol. Biochem. Biophys. Res. Commun. 41, 615-620 (1970). 

ChenH, Howald WN, and Juchau MR (2000) Biosynthesis of all-fraws-retinoic acid from all-fraws-retinol catalysis ofall-trfl s-retinol oxidation by human P-450 cytochromes. Drug Metabolism and Disposal 28, 315-22. 

Kurlandsky SB, Duell EA, Kang S, Voorhees JJ, and Fisher GJ (1996) Auto-regulation of retinoic acid biosynthesis through regulation of retinol esterification in human keratinocytes./owrna/ of Biological Chemistry 271,15346-52. 

Napoli J and Race K (1987) The biosynthesis of retinoic acid from retinol by rat tissues. Archives of Biochemistry and Biophysics 255, 95-101. 

Soprano DR, Smith JF, and Goodman DS (1982) Effect of retinol status on retinol-binding protein biosynthesis rate and translatable messenger RNA level in rat liver. Journal of... 

Figure 11 Biosynthesis of isoprenoid type cofactors. 18, Heme a 39, pyridoxal 5 -phosphate 43, 1-deoxy-D-xylulose 5-phosphate 46, thiamine pyrophosphate 83, acetyl-CoA 84, (S)-3-hydroxy-3-methylglutaryl-CoA 85, mevalonate 86, isopentenyl diphosphate (IPP) 87, dimethylallyl diphosphate (DMAPP) 88, pyruvate 89, D-glyceraldehyde 3-phosphate 90, 2C-methyl-D-erythritol 4-phosphate 91, 2C-methyl-erythritol 2,4-cyclodiphosphate 92, 1-hydroxy-2-methyl-2-( )-butenyl 4-diphosphate 93, polyprenyl diphosphate 94, cholecalciferol 95, fS-carotene 96, retinol 97, ubiquinone 98, menaquinone 99, a-tocopherol.

The effect of inhibitors on the biosynthesis of rubixanthin (114) and other hydroxylated carotenoids was studiedin Staphylococcus aureus. Retinol was metabolized in rat livers to give an acidic product which was allegedly different from retinoic acid. 

Biochemical research has shown the importance of zinc metabolism in the retina (9). Zinc is found in high concentrations in the choroid, the retina, and especially the ganglion cells. Retinol dehydrogenase, a zinc-containing enzyme, interferes with the transformation of retinol (vitamin Ai), which is essential for color sensation and conal vision. Furthermore, zinc is involved in the biosynthesis of the specific transport of retinol from the liver to the effector cells. Ethambutol is a chelating... 

Unlike many retinol dehydrogenases, the enzyme that catalyzes the conversion of retinol to anhydroretinol, retinol dehydratase, does not use CRBP-retinol as a substrate rather, it uses free retinol (49-51). However, the enzyme responsible for biosynthesis of 14-hydroxy-4,14-retro-retinol has not yet been isolated. 

Vitamin A - also called all-tra/75 -retinol, is an isoprenoid alcohol that plays a key role in vision and a role in controlling animal growth. Vitamin A must either be present in the diet, or derived from / -carotene, an isoprenoid compound prominent in carrots. See Figure 19.25 for the biosynthesis of dX -trans-xQtmo. Dehydrogenation of retinol yields the aldehyde, retinal, which has a role in vision. Another derivative of retinol is retinoic acid, which can be made by the oxidation of retinal. 

Terpenes contain multiples of five carbons since they are synthesized by linking together isoprene units. The isoprene unit is a branched C, unit. Vitamins A (trans -retinol), D, and E are terpenes. Other terpenes are intermediates in the biosynthesis of cholesterol. 

Fig. 102.2 Biosynthesis of retinol by the break of the central double bond of P-carotene...

Bhat, P. V. 2005. Role of retinol dehydrogenase type 1 (RALDHl) in retinoic acid biosynthesis. Enzymol Mol Biol 12 66-72. 

Biosynthesis, Absorption, and Hepatic Metabolism of Retinol DeWitt S. Goodman and William S. Blaner... 

Another important question is whether deposited carotenoids are utilizable for biosynthesis of retinol by extramucosal tissue. Dioxygenase has been demonstrated in vivo from liver homogenates and, therefore, extramucosal conversion is possible. Alternatively, although unlikely, biosynthesis of retinol from absorbed carotenoids could occur by way of an enterohepatic circulatory route as speculated by Patwardhan (1969). When a chronic dietary lack of vitamin A occurs, carotenoid deposits could serve to delay the onset of deficiency and could account in part for the wide variance in the appearance of deficiency signs noted among individuals consuming inadequate diets. However, although carotenoids are found deposited in the liver, they are not reported to be constituents of bile (Gal etaL, 1972). 

Posch, K. C, Burns, R B, and Napoli, J L. (1992) Biosynthesis of d -trans-retinoic acid from retinal recognition of retinal bound to cellular retinol binding protein (type I) as substrate by a purified cytosolic dehydrogenase J Biol Chem. 267, 19,676-19,682... 

The aim of this chapter is to summarize our current knowledge of the biosynthesis, the intestinal absorption, and the hepatic metabolism of retinol. 

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