Cholesterol 7 alpha-hydroxylase
Encyclopedia
Cholesterol 7 alpha-hydroxylase also known as cholesterol 7-alpha-monooxygenase or cytochrome P450 7A1 (CYP7A1) is an enzyme
that in humans is encoded by the CYP7A1 gene
.
from cholesterol
via the classic pathway, catalyzing the formation of 7-alpha-hydroxycholesterol
. CYP7A1 is a cytochrome P450 heme
enzyme
that oxidizes cholesterol using molecular oxygen
.
It is downregulated by Sterol regulatory element-binding proteins (SREBP) when plasma cholesterol levels are low. It is upregulated by the nuclear receptor LXR
(liver X receptor) when cholesterol (to be specific, oxysterol) levels are high.
The effect of this upregulation is to increase the production of bile acids and reduce the level of cholesterol in hepatocytes.
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that in humans is encoded by the CYP7A1 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Function
Cholesterol 7 alpha-hydroxylase is the rate-limiting enzyme in the synthesis of bile acidBile acid
Bile acids are steroid acids found predominantly in the bile of mammals. Bile salts are bile acids compounded with a cation, usually sodium. In humans, the salts of taurocholic acid and glycocholic acid represent approximately eighty percent of all bile salts. The two major bile acids are cholic...
from cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
via the classic pathway, catalyzing the formation of 7-alpha-hydroxycholesterol
7-alpha-hydroxycholesterol
7α-Hydroxycholesterol is a precursor of bile acids, created by cholesterol 7 alpha-hydroxylase. It is the rate-determining step....
. CYP7A1 is a cytochrome P450 heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that oxidizes cholesterol using molecular oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
.
It is downregulated by Sterol regulatory element-binding proteins (SREBP) when plasma cholesterol levels are low. It is upregulated by the nuclear receptor LXR
Liver X receptor
The liver X receptor is a member of the nuclear receptor family of transcription factors and is closely related to nuclear receptors such as the PPARs, FXR and RXR. Liver X receptors are important regulators of cholesterol, fatty acid, and glucose homeostasis...
(liver X receptor) when cholesterol (to be specific, oxysterol) levels are high.
The effect of this upregulation is to increase the production of bile acids and reduce the level of cholesterol in hepatocytes.