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25-Hydroxyvitamin D 1-alpha-hydroxylase (VD 1A hydroxylase) also known as calcidiol 1-monooxygenase [5] or cytochrome p450 27B1 (CYP27B1) or simply 1-alpha-hydroxylase is a cytochrome P450 enzyme that in humans is encoded by the CYP27B1 gene. [6] [7] [8]
In medical practice, a blood test for 25-hydroxy-vitamin D, 25(OH)D, is used to determine an individual's vitamin D status. [11] The name 25(OH)D refers to any combination of calcifediol (25-hydroxy-cholecalciferol), derived from vitamin D 3, and ercalcidiol (25-hydroxy-ergocalciferol), [1] derived from vitamin D 2. The first of these (also ...
A third important effect of PTH on the kidneys is stimulation of the conversion of 25-hydroxy vitamin D into 1,25-dihydroxy vitamin D (calcitriol). [216] This form of vitamin D is the active hormone which promotes calcium uptake from the intestine via the action of calbindin. [218] Calcitriol also reduces calcium loss to urine. [215]
Vitamin D toxicity, or hypervitaminosis D, is the toxic state of an excess of vitamin D.The normal range for blood concentration of 25-hydroxyvitamin D in adults is 20 to 50 nanograms per milliliter (ng/mL).
Vitamin D deficiency is typically diagnosed by measuring the concentration of the 25-hydroxyvitamin D in the blood, which is the most accurate measure of stores of vitamin D in the body. [ 1 ] [ 7 ] [ 2 ] One nanogram per millilitre ( 1 ng/mL ) is equivalent to 2.5 nanomoles per litre ( 2.5 nmol/L ).
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]
Calcitriol is a hormone and the active form of vitamin D, normally made in the kidney. [8] [9] [10] It is also known as 1,25-dihydroxycholecalciferol.It binds to and activates the vitamin D receptor in the nucleus of the cell, which then increases the expression of many genes. [11]
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 ...