Pharmacognosy with the Basics of Plant Biochemistry - Kovalyov V. M. 2004

Special Part
Vitamins
Alicyclic Vitamins

Retinols (vitamin A, antixerophthalmic factor). This group comprises compounds consisting of 20 carbon atoms. Vitamin A is a derivative of a trimethylcyclohexane ring linked to an aliphatic chain terminating in an alcohol group.

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Vitamin A

Fish oil serves as its primary source. Retinol is absent in plants; however, many plant species (such as carrots, parsley, green onions, sorrel, red pepper, black currant, rose hips, gooseberries, tomatoes, and apricots) contain carotenes, which are provitamins of retinol.

Carotenes constitute one of the Major Groups of carotenoids, chemically classified as tetraterpenes (С₄₀Н₆₄). In plants, carotene may occur in three isomeric forms: a-, ß-, and y-carotene. They act as active oxygen carriers, which explains the presence of numerous oxygenated carotene derivatives in plants, including epoxides in the carotene rings that readily release their oxygen.

In plants, carotenes are localized in chromoplasts—Plastids of fruits, flowers, and other plant parts—as well as in METABOLISM/14.html">Chloroplasts alongside chlorophyll in the form of Water-soluble Structure/178.html">Protein Complexes or within fatty oil droplets. The ß-isomer is the most widely distributed carotene. In the living Organism, the ß-carotene molecule undergoes hydrolytic Cleavage into two symmetrical halves, yielding two molecules of vitamin A. This transformation takes place in the intestinal mucosa under the catalytic action of the enzyme carotenase.

ß-Carotene

Both a- and y-carotenes yield only a single molecule of vitamin A upon cleavage, as these isomers possess only one ß-ionone ring each. ß-Carotene is the most valuable, as it generates two molecules of retinol.

The carotene content in plants depends on the vegetation period, environmental conditions, climate, Temperature, and types of fertilizers applied. Highly valuable sources of carotene are those plants in which it accumulates in significant quantities. Some of these (such as carrots and pumpkins) serve as industrial raw Materials for the extraction of pure carotenes, while others are used to produce crude total extracts.

Vitamin A enters The Human Body in its ready-to-use form exclusively through The oxidation of animal fats. A deficiency of vitamin A manifests as dry and pale Skin, brittle Nails and Hair, degenerative changes in mucous membranes, increased fatigue, and visual impairments. The recommended daily allowance is 1-2.7 mg.

Vitamin D (antirachitic factor) is a collective term encompassing several substances (Vitamins D₁, D₂, D₃, D₄) with closely related chemical and biological properties. Phytosterols act as precursors to the Vitamin D Group. Ingested via plant-based foods into animal organisms, they are converted into cholesterols, which subsequently give rise to specific vitamins. For instance, ergosterol found in Yeast is transformed into vitamin D₂ within the animal body.

Other vitamins of the D group are formed in a similar manner. Naturally occurring vitamins D₂ and D₃ accumulate in substantial amounts in The Liver and adipose tissue of cod and marine animals.

The biochemical role of vitamin D is closely linked to The regulation of Calcium and phosphorus metabolism. Its deficiency leads to Rickets in children and Osteomalacia in adults.

The daily requirement is 400 IU (1 International Unit corresponds to 0.025 µg of ergo- or cholecalciferol).