In biochemistry, a lyase is an enzyme that catalyzes the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. For example, an enzyme that catalyzed this reaction would be a lyase:

ATP → cAMP + PP_i

Lyases differ from other enzymes in that they require only one substrate for the reaction in one direction, but two substrates for the reverse reaction.

1 Nomenclature
2 Classification
3 See also
4 References

Nomenclature [link]

Systematic names are formed as "substrate group lyase." Common names include decarboxylase, dehydratase, aldolase, etc. When the reverse reaction is more important, synthase may be used in the name.

Classification [link]

Lyases are classified as EC 4 in the EC number classification of enzymes. Lyases can be further classified into seven subclasses:

EC 4.1 includes lyases that cleave carbon-carbon bonds, such as decarboxylases (EC 4.1.1), aldehyde lyases (EC 4.1.2), oxo acid lyases(EC 4.1.3) and others (EC 4.1.99)
EC 4.2 includes lyases that cleave carbon-oxygen bonds, such as dehydratases
EC 4.3 includes lyases that cleave carbon-nitrogen bonds
EC 4.4 includes lyases that cleave carbon-sulfur bonds
EC 4.5 includes lyases that cleave carbon-halide bonds
EC 4.6 includes lyases that cleave phosphorus-oxygen bonds, such as adenylate cyclase and guanylate cyclase
EC 4.99 includes other lyases, such as ferrochelatase

References [link]

EC 4 Introduction from the Department of Chemistry at Queen Mary, University of London

Proteins: enzymes

Topics

Active site · Allosteric regulation · Binding site · Catalytically perfect enzyme · Coenzyme · Cofactor · Cooperativity · EC number · Enzyme catalysis · Enzyme inhibitor · Enzyme kinetics · Lineweaver–Burk plot · Michaelis–Menten kinetics · List of enzymes

Types

EC1 Oxidoreductases/list · EC2 Transferases/list · EC3 Hydrolases/list · EC4 Lyases/list · EC5 Isomerases/list · EC6 Ligases/list

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Carbon-carbon lyases (EC 4.1)

4.1.1: Carboxy-lyases

Pyruvate decarboxylase · Oxaloacetate decarboxylase · Acetoacetate decarboxylase · Malonyl-CoA decarboxylase · Glutamate decarboxylase · Ornithine decarboxylase · Lysine decarboxylase · Phosphoribosylaminoimidazole carboxylase · Histidine decarboxylase · Uridine monophosphate synthetase/Orotidine 5'-phosphate decarboxylase · Aromatic L-amino acid decarboxylase · Phosphoenolpyruvate carboxylase · Pyrophosphomevalonate decarboxylase · Uroporphyrinogen III decarboxylase · RuBisCO · Phosphoenolpyruvate carboxykinase · Adenosylmethionine decarboxylase

4.1.2: Aldehyde-lyases

Aldolase (Aldolase A, Aldolase B, Aldolase C) · 2-hydroxyphytanoyl-CoA lyase · Threonine aldolase

4.1.3: Oxo-acid-lyases

3-hydroxy-3-methylglutaryl-CoA lyase

4.1.99: Other

Tryptophanase

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Carbon-oxygen lyases (EC 4.2) (primarily dehydratases)

4.2.1: Hydro-Lyases

Carbonic anhydrase - Fumarase - Aconitase - Enolase (Alpha, Enolase 2) - Enoyl-CoA hydratase/3-Hydroxyacyl ACP dehydrase - Methylglutaconyl-CoA hydratase - Tryptophan synthase - Cystathionine beta synthase - Porphobilinogen synthase - 3-isopropylmalate dehydratase - Urocanate hydratase - Uroporphyrinogen III synthase - Nitrile hydratase

4.2.2: Acting on polysaccharides

Hyaluronate lyase

4.2.3: Acting on phosphates

Threonine synthase

4.2.99: Other

Carboxymethyloxysuccinate lyase

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Carbon-nitrogen lyases (EC 4.3)

4.3.1: ammonia-lyases

Histidine ammonia-lyase - Formiminotransferase cyclodeaminase - Serine dehydratase

4.3.2: amidine-lyases

Argininosuccinate lyase - Adenylosuccinate lyase

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Carbon-sulfur lyases (EC 4.4)

4.4.1

Cystathionine gamma-lyase - Cystathionine-beta-lyase - Leukotriene C4 synthase

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Carbon-halide lyases (EC 4.5)

4.5.1

Dichloromethane dehalogenase - Halohydrin dehalogenase

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Phosphorus-oxygen lyases (EC 4.6)

4.6.1

Adenylate cyclase (4.6.1.1)	intracellular: ADCY1 · ADCY2 · ADCY3 · ADCY4 · ADCY5 · ADCY6 · ADCY7 · ADCY8 · ADCY9 · ADCY10 Extracellular adenylate cyclase

Guanylate cyclase (4.6.1.2)	soluble guanylyl cyclase: GUCY1A2 · GUCY1A3 · GUCY1B2 · GUCY1B3 guanylate cyclase-coupled receptor: GUCY2C · GUCY2D · ANP (NPR1 · NPR2)

Other	Cytidylate cyclase · 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase · Phosphatidylinositol diacylglycerol-lyase · Glycosylphosphatidylinositol diacylglycerol-lyase · FAD-AMP lyase (cyclizing)

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CYP17A1

Cytochrome P450 17A1, or steroid 17-alpha-monooxygenase, or 17α-hydroxylase/17,20 lyase/17,20 desmolase is an enzyme that in humans is encoded by the CYP17A1 gene. It is found in the zona reticularis of the adrenal cortex and zona fasciculata as well as gonadal tissues. This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are generally regarded as monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids, including the remarkable carbon-carbon bond scission catalyzed by this enzyme. This protein localizes to the endoplasmic reticulum. It has both 17alpha-hydroxylase and 17,20-lyase activities, and is a key enzyme in the steroidogenic pathway that produces progestins, mineralocorticoids, glucocorticoids, androgens, and estrogens.

More specifically, CYP17A1 acts upon pregnenolone and progesterone to add a hydroxyl (-OH) group at carbon 17 of the steroid D ring (the hydroxylase activity), or acts upon 17-hydroxyprogesterone and 17-hydroxypregnenolone to split the side-chain off the steroid nucleus (the lyase activity).

This page contains text from Wikipedia, the Free Encyclopedia - https://wn.com/CYP17A1