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CYP2R1 is cytochrome P450 2R1, an enzyme which is the principal vitamin D 25-hydroxylase. [5] [6] In humans it is encoded by the CYP2R1 gene located on chromosome 11p15.2. [7]It is expressed in the endoplasmic reticulum in liver, where it performs the first step in the activation of vitamin D by catalyzing the formation of 25-hydroxyvitamin D. [8]
Vitamin D 3 (cholecalciferol) is produced industrially by exposing 7-dehydrocholesterol to UVB and UVC light, followed by purification. The 7-dehydrocholesterol is sourced as an extraction from lanolin, a waxy skin secretion in sheep's wool. [184] Vitamin D 2 (ergocalciferol) is produced in a similar way using ergosterol from yeast as a ...
Cholecalciferol is a form of vitamin D which is naturally synthesized in skin and functions as a pro-hormone, being converted to calcitriol. This is important for maintaining calcium levels and promoting bone health and development. [4] As a medication, cholecalciferol may be taken as a dietary supplement to prevent or to treat vitamin D ...
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).
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 ...
Calcifediol binds in the blood to vitamin D-binding protein (also known as gc-globulin) and is the main circulating vitamin D metabolite. [4] [5] Calcifediol has an elimination half-life of around 15 to 30 days. [4] [9] Calcifediol is further hydroxylated at the 1-alpha-position in the kidneys to form 1,25-(OH) 2 D 3, calcitriol.
The kidney influences the plasma ionized calcium concentration in yet another manner. It processes vitamin D 3 into calcitriol, the active form that is most effective in promoting the intestinal absorption of calcium. This conversion of vitamin D 3 into calcitriol, is also promoted by high plasma parathyroid hormone levels. [4] [5]
The vitamin D receptor (VDR also known as the calcitriol receptor) is a member of the nuclear receptor family of transcription factors. [5] Calcitriol (the active form of vitamin D , 1,25-(OH) 2 vitamin D 3 ) binds to VDR, which then forms a heterodimer with the retinoid-X receptor .