CYP27A1

(redirected from 25-hydroxylase)

CYP27A1

A gene on chromosome 2q33-qter that encodes a member of the cytochrome P450 superfamily of enzymes, which catalyse reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. CYP27A1 is a mitochondrial protein that oxidises cholesterol intermediates as part of the bile-synthesis pathway. It catalyses the first step in the oxidation of the side chain of sterol intermediates and has a vitamin D3-25-hydroxylase activity. Because the conversion of cholesterol to bile acids is the major route for eliminating cholesterol from the body, CYP27A1 is important for cholesterol homeostasis.

Molecular pathology
CYP27A1 mutations cause cerebrotendinous xanthomatosis.
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The first step occurs in the liver, where vitamin D is hydroxylated to 25-hydroxyvitamin D (25-OHD) by hepatic 25-hydroxylase. The second step occurs mainly in the kidney, where 25-OHD is further hydroxylated by the mitochondrial vitamin D 1[alpha]-hydroxylase to the biologically active hormone 1,25-dihydroxyvitamin D (1,25-[OH.sub.2]D), which binds to its nuclear receptor and exerts its biological activities (1,2,3).
Besides, the enzymes such as 1-hydroxylase and 25-hydroxylase that are involved in formation of an active form of this vitamin are low in persons with high BMI.
1-[alpha]-hydroxylase (CYP27B1) and 25-hydroxylase convert vitamin D to its active form, 1,25 dihydroxy-vitamin [D.sub.3] (1, 25[(OH).sub.2][D.sub.3]), which exerts its effect by combining with the nuclear vitamin [D.sub.3] receptor (VDR).
It is basically a hormone obtained after hydroxylation at carbon number 25 by enzyme 25-hydroxylase in the liver to form 25-hydroxyvitamin D, followed by another hydroxylation at carbon number 1 by the enzyme 1a hydroxylase to form, 1,25-dihydroxyvitamin D, active form vitamin D.
The enzyme vitamin D 25-hydroxylase metabolizes ergocalciferol and cholecalciferol in the liver and converts them to the 25(OH)D forms of 25(OH)D2 and 25(OH)[D.sub.3], respectively.
The formation of 25-OHC is catalyzed by the enzyme cholesterol 25-hydroxylase (Ch25h) [29, 30].
The release of IFN-[gamma], a T helper- (Th-)1 cytokine that is central to regulating the obesity-induced adipose tissue inflammatory response [36, 37], upregulates the production of 25-hydroxycholesterol by increased 25-hydroxylase activity [38].
10 demonstrated the inhibition by PIs of the 25-hydroxylase and the 1a-hydroxylase involved in vitamin D metabolism.
In addition, there is reason to believe that 25(OH)D is a marker both of gonadal function (vitamin D is 25-hydroxylated by gonadal tissues) and of the capacity of the liver to detoxify xenobiotics (hepatic 25-hydroxylase enzymes are also involved in phase 1 detoxification pathways).
From here, vitamin D3 is transported to your liver, where it is combined with the 25-hydroxylase enzyme to form calcidiol (25-hydroxycholecalciferol or 25-hydroxyvitamin D).