Squalene epoxidase | |||||||||
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Identifiers | |||||||||
EC no. | 1.14.13.132 | ||||||||
CAS no. | 9029-62-3 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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SQLE | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Identifiers | |||||||||||||||||||||||||||||||||||||||||||||||||||
Aliases | SQLE , entrez:6713, squalene epoxidase | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 602019 MGI: 109296 HomoloGene: 2355 GeneCards: SQLE | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Wikidata | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Squalene monooxygenase (also called squalene epoxidase) is a eukaryotic enzyme that uses NADPH and diatomic oxygen to oxidize squalene to 2,3-oxidosqualene (squalene epoxide). Squalene epoxidase catalyzes the first oxygenation step in sterol biosynthesis and is thought to be one of the rate-limiting enzymes in this pathway. [5] In humans, squalene epoxidase is encoded by the SQLE gene. [6] Several eukaryote genomes lack a squalene monooxygenase encoding gene, but instead encode an alternative squalene epoxidase that performs the same task. [7]
The canonical squalene monooxygenase is a flavoprotein monooxygenase. Flavoprotein monooxygenase form flavin hydroperoxides at the enzyme active site, which then transfer the terminal oxygen atom of the hydroperoxide to the substrate. Squalene monooxygenase differs from other flavin monooxygenases in that the oxygen is inserted into the substrate as an epoxide rather than as a hydroxyl group. This enzyme contains a loosely bound FAD flavin and obtains electrons from NADPH-cytochrome P450 reductase, rather than binding NADPH directly. The alternative squalene epoxidase belongs to the fatty acid hydroxylase superfamily and obtains electrons from cytochrome b5. [7]
Inhibitors of squalene epoxidase have found application mainly as antifungal drugs: [8]
Since squalene epoxidase is on the biosynthetic pathway leading to cholesterol, inhibitors of this enzyme may also find application in treatment of hypercholesterolemia. [10]
In baker's yeast ( Saccharomyces cerevisiae ), squalene epoxidase is localized to both the endoplasmic reticulum and lipid droplets. Only the ER localized protein is active.
Squalene epoxidase also catalyzes the formation of diepoxysqualene (DOS). DOS is converted to 24(S),25-epoxylanosterol by lanosterol synthase.
Cholesterol side-chain cleavage enzyme is commonly referred to as P450scc, where "scc" is an acronym for side-chain cleavage. P450scc is a mitochondrial enzyme that catalyzes conversion of cholesterol to pregnenolone. This is the first reaction in the process of steroidogenesis in all mammalian tissues that specialize in the production of various steroid hormones.
Steroid 11β-hydroxylase, also known as steroid 11β-monooxygenase, is a steroid hydroxylase found in the zona glomerulosa and zona fasciculata of the adrenal cortex. Named officially the cytochrome P450 11B1, mitochondrial, it is a protein that in humans is encoded by the CYP11B1 gene. The enzyme is involved in the biosynthesis of adrenal corticosteroids by catalyzing the addition of hydroxyl groups during oxidation reactions.
Squalene synthase (SQS) or farnesyl-diphosphate:farnesyl-diphosphate farnesyl transferase is an enzyme localized to the membrane of the endoplasmic reticulum. SQS participates in the isoprenoid biosynthetic pathway, catalyzing a two-step reaction in which two identical molecules of farnesyl pyrophosphate (FPP) are converted into squalene, with the consumption of NADPH. Catalysis by SQS is the first committed step in sterol synthesis, since the squalene produced is converted exclusively into various sterols, such as cholesterol, via a complex, multi-step pathway. SQS belongs to squalene/phytoene synthase family of proteins.
Flavin-containing monooxygenase 3 (FMO3), also known as dimethylaniline monooxygenase [N-oxide-forming] 3 and trimethylamine monooxygenase, is a flavoprotein enzyme (EC 1.14.13.148) that in humans is encoded by the FMO3 gene. This enzyme catalyzes the following chemical reaction, among others:
NAD+ kinase (EC 2.7.1.23, NADK) is an enzyme that converts nicotinamide adenine dinucleotide (NAD+) into NADP+ through phosphorylating the NAD+ coenzyme. NADP+ is an essential coenzyme that is reduced to NADPH primarily by the pentose phosphate pathway to provide reducing power in biosynthetic processes such as fatty acid biosynthesis and nucleotide synthesis. The structure of the NADK from the archaean Archaeoglobus fulgidus has been determined.
In enzymology, a kynurenine 3-monooxygenase (EC 1.14.13.9) is an enzyme that catalyzes the chemical reaction
SEC14L2 is a gene that, in humans, encodes the protein SEC14-like protein 2.
Carbonyl reductase 1, also known as CBR1, is an enzyme which in humans is encoded by the CBR1 gene. The protein encoded by this gene belongs to the short-chain dehydrogenases/reductases (SDR) family, which function as NADPH-dependent oxidoreductases having wide specificity for carbonyl compounds, such as quinones, prostaglandins, and various xenobiotics. Alternatively spliced transcript variants have been found for this gene.
Adrenodoxin reductase, was first isolated from bovine adrenal cortex where it functions as the first enzyme in the mitochondrial P450 systems that catalyze essential steps in steroid hormone biosynthesis. Examination of complete genome sequences revealed that adrenodoxin reductase gene is present in most metazoans and prokaryotes.
Dimethylaniline monooxygenase [N-oxide-forming] 1 is an enzyme that in humans is encoded by the FMO1 gene.
Dimethylaniline monooxygenase [N-oxide-forming] 5 is an enzyme that in humans is encoded by the FMO5 gene.
Dimethylaniline monooxygenase [N-oxide-forming] 2 is an enzyme that in humans is encoded by the FMO2 gene.
Dimethylaniline monooxygenase [N-oxide-forming] 4 is an enzyme that in humans is encoded by the FMO4 gene.
Cytochrome P450 4F12 is a protein that in humans is encoded by the CYP4F12 gene.
L-asparaginase is an enzyme that in humans is encoded by the ASRGL1 gene.
Kynurenine 3-monooxygenase is an enzyme that in humans is encoded by the KMO gene.
CYP4F22 is a protein that in humans is encoded by the CYP4F22 gene.
Acetyl-CoA acetyltransferase, cytosolic, also known as cytosolic acetoacetyl-CoA thiolase, is an enzyme that in humans is encoded by the ACAT2 gene
The flavin-containing monooxygenase (FMO) protein family specializes in the oxidation of xeno-substrates in order to facilitate the excretion of these compounds from living organisms. These enzymes can oxidize a wide array of heteroatoms, particularly soft nucleophiles, such as amines, sulfides, and phosphites. This reaction requires an oxygen, an NADPH cofactor, and an FAD prosthetic group. FMOs share several structural features, such as a NADPH binding domain, FAD binding domain, and a conserved arginine residue present in the active site. Recently, FMO enzymes have received a great deal of attention from the pharmaceutical industry both as a drug target for various diseases and as a means to metabolize pro-drug compounds into active pharmaceuticals. These monooxygenases are often misclassified because they share activity profiles similar to those of cytochrome P450 (CYP450), which is the major contributor to oxidative xenobiotic metabolism. However, a key difference between the two enzymes lies in how they proceed to oxidize their respective substrates; CYP enzymes make use of an oxygenated heme prosthetic group, while the FMO family utilizes FAD to oxidize its substrates.
Biliverdin reductase B is a protein that in humans is encoded by the BLVRB gene.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.