What is 25 hydroxylation of vitamin D?
Vitamin D is metabolized first to 25 hydroxyvitamin D (25OHD), then to the hormonal form 1,25-dihydroxyvitamin D (1,25(OH)2D). CYP2R1 is the most important 25-hydroxylase; CYP27B1 is the key 1-hydroxylase. Both 25OHD and 1,25(OH)2D are catabolized by CYP24A1.
What is hydroxylation of Calciferol?
Cholecalciferol (vitamin Da) undergoes an obligatory two- step hydroxylation which is carried out sequentially first in the liver and then in the kidney, where 25-hydroxychole- calciferol-1-hydroxylase catalyzes the production of the biologically active form of vitamin Ds, 1,25-dihydroxychole- calciferol.
Where does vitamin D 25 hydroxylation occur?
the liver
The first step, 25-hydroxylation, takes place primarily in the liver, although other tissues have this enzymatic activity as well. As will be discussed below, there are several 25-hydroxylases. 25OHD is the major circulating form of vitamin D.
What is vitamin D hydroxylation?
Vitamin D from the diet, or from skin synthesis, is biologically inactive. It is activated by two protein enzyme hydroxylation steps, the first in the liver and the second in the kidneys.
How is cholecalciferol synthesized in the body?
While it can also be obtained from dietary sources or supplements, vitamin D3 (cholecalciferol) is synthesized in the human skin from 7-dehydrocholesterol upon exposure to ultraviolet-B (UVB) radiation from sunlight (see the separate article on Vitamin D and Skin Health).
What is the normal range of 25-hydroxyvitamin D?
Normal Results The normal range of vitamin D is measured as nanograms per milliliter (ng/mL). Many experts recommend a level between 20 and 40 ng/mL. Others recommend a level between 30 and 50 ng/mL.
What is another name for the 25 hydroxylated form of cholecalciferol?
There are four different forms of vitamin D: calcifediol, which is 25-hydroxylated form of cholecalciferol; calcitriol, which is 1,25 dihydroxylated form of cholecalciferol; and ergocalciferol, which is vitamin D2—dihydrotachysterol—a vitamin D analog.
Is cholecalciferol active vitamin D?
The preferred vitamin D analog for daily supplementation is cholecalciferol (vitamin D3). The active form of vitamin D3 is 1,25-dihydroxy-vitamin D3. Alfacalcidol, calcitriol and eldecalcitol are used to treat osteoporosis in Japan.
What happens in a hydroxylation reaction?
Summary. Hydroxylation is an oxidation reaction in which carbon–hydrogen (CH) bond oxidizes into carbon–hydroxyl (COH) bond. In organic chemistry, the hydroxylation reaction is mostly mediated by catalysts and heat. Most often the catalysts that mediates the hydroxylation reactions are metal ions.
What is the purpose of hydroxylation?
Hydroxylation is important in detoxification since it converts lipophilic compounds into water-soluble (hydrophilic) products that are more readily removed by the kidneys or liver and excreted. Some drugs (for example, steroids) are activated or deactivated by hydroxylation.
How is vitamin D synthesized in the skin?
The skin is responsible for producing vitamin D. During exposure to sunlight, ultraviolet radiation penetrates into the epidermis and photolyzes provitamin D3 to previtamin D3. Previtamin D3 can either isomerize to vitamin D3 or be photolyzed to lymisterol and tachysterol.
How much Cholecalciferol is in the human body?
These data suggest that, at typical vitamin D 3 inputs and serum concentrations, there is very little native cholecalciferol in the body, and 25 (OH)D constitutes the bulk of vitamin D reserves.
Is there a limit to the first-order 25-hydroxylation of vitamin D 3?
Taken together, these results show that, as is typical for enzyme systems, there is a practical limit to the first-order 25-hydroxylation of vitamin D 3 and that, when vitamin D 3 input exceeds that limit, vitamin D 3 itself accumulates within the body, both in serum and probably in body fat.
How is 25 (OH) D3 partitioned in the human body?
However, the partition in the body between the native compound and its 25-hydroxy derivative [25 (OH)D 3] at various inputs in humans is largely unknown, as are the kinetics of the conversion in vivo.