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retinol:see Vitamin A under vitaminvitamin,
group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes.
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(also called axerophthol or vitamin A), an isoprenoid whose chemical formula is C20H30O. Retinol is soluble in nonpolar organic solvents, insoluble in water, and has a melting point of 63°–64°C. In animals and man, it is converted from the carotene in food and stored mainly in the liver; it is particularly abundant in the liver of whales and fish and in fish oil.
The most important biological function of retinol is its participation in the form of retinal in the visual process. A retinol deficiency results in impairment of twilight vision (night blindness, or nyctalopia) and in injury to epithelial tissue, as in xe-rophthalmia. An excess of retinol causes a variety of metabolic disturbances, an accumulation of retinol in the hydrophobic fraction of cell membranes, and destruction of these membranes. Retinol is commercially synthesized from β-ionone. Retinol is sometimes called vitamin A1; its dehydro derivative C20H28O is called vitamin A2. Retinal1 and retinal2 are distinguished accordingly.