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The conversion of vitamin D, especially cholecalciferol, to 25(OH)D (calcifediol) is one of the key steps in the vitamin D hormonal system. The CYP2R1 enzymatic activity achieving this process was previously thought to be constitutively expressed and stable, so that serum 25(OH)D was a measure of the supply of vitamin D. [9]
The conversion from ergosterol to vitamin D 2 follows a similar procedure, forming previtamin D 2 by photolysis, which isomerizes to vitamin D 2 (ergocalciferol). [165] The transformation of previtamin D 2 to vitamin D 2 in methanol has a rate comparable to that of previtamin D 3 .
7-Dehydrocholesterol (7-DHC) is a zoosterol that functions in the serum as a cholesterol precursor, and is photochemically converted to vitamin D 3 in the skin, therefore functioning as provitamin-D 3. The presence of this compound in human skin enables humans to manufacture vitamin D 3 (cholecalciferol).
CYP24A1 also is able to catalyze another pathway which starts with 23-hydroxylation of 1,25-(OH) 2 D 3 and culminates in 1,25-(OH) 2 D 3-26,23-lactone. [ 6 ] The side chains of the ergocalciferol (vitamin D 2 ) derivatives, 25-OH-D 2 and 1,25-(OH) 2 D 2 , are also hydroxylated by CYP24A1.
Previtamin D 3 is an intermediate in the production of cholecalciferol (vitamin D 3). It is formed by the action of UV light, most specifically UVB light of wavelengths between 295 and 300 nm, acting on 7-dehydrocholesterol in the epidermal layers of the skin. [1] [2] [3] The B ring of the steroid nucleus structure is broken open, making a ...
24,25-Dihydroxycholecalciferol, also known as 24,25-dihydroxyvitamin D 3 and (24R)-hydroxycalcidiol (abbreviated as 24(R),25-(OH) 2 D 3), [1] is a compound which is closely related to 1,25-dihydroxyvitamin D 3, the active form of vitamin D 3. Like vitamin D 3 itself and calcifediol (25-hydroxyvitamin D 3), it is inactive as a hormone both in ...
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The KEGG PATHWAY database is a collection of manually drawn pathway maps for metabolism, genetic information processing, environmental information processing such as signal transduction, ligand–receptor interaction and cell communication, various other cellular processes and human diseases, all based on extensive survey of published literature.