In enzymology, a cystathionine gamma-synthase () is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that catalyzes the formation of

cystathionine Cystathionine is an intermediate in the synthesis of cysteine. Cystathionine is produced by the transsulfuration pathway which converts homocysteine into cystathionine. Cystathionine is then used by the enzymes cystathionine gamma-lyase (CTH), ...

from cysteine and an activated derivative of

homoserine Homoserine (also called isothreonine) is an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2OH. -Homoserine is not one of the common amino acids encoded by DNA. It differs from the proteinogenic amino acid serine by insertion of an additi ...

, e.g.: :''O''⁴-succinyl-L-homoserine + L-cysteine

\longrightarrow

L-cystathionine + succinate : Cystathionine_gamma-synthase

In microorganisms, the activated substrate of this enzyme is O4-succinyl-L-homoserine or O4-acetyl-L-homoserine. Cystathionine gamma-synthase from plants uses L-homoserine phosphate instead. This enzyme belongs to the family of

transferase A transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved in hundreds of ...

s, specifically those transferring aryl or alkyl groups other than methyl groups. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is O4-succinyl-L-homoserine:L-cysteine S-(3-amino-3-carboxypropyl)transferase. Other names in common use include O-succinyl-L-homoserine succinate-lyase (adding cysteine), O-succinylhomoserine (thiol)-lyase, homoserine O-transsuccinylase, O-succinylhomoserine synthase, O-succinylhomoserine synthetase, cystathionine synthase, cystathionine synthetase, homoserine transsuccinylase, 4-O-succinyl-L-homoserine:L-cysteine, and S-(3-amino-3-carboxypropyl)transferase. This enzyme participates in 4

metabolic pathways In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical re ...

methionine metabolism Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical ro ...

cysteine metabolism Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.cysteine is metabolism creating complex systems ...

, selenoamino acid metabolism, and

sulfur metabolism Sulfur is metabolized by all organisms, from bacteria and archaea to plants and animals. Sulfur is reduced or oxidized by organisms in a variety of forms. The element is present in proteins, sulfate esters of polysaccharides, steroids, ph ...

. It employs one cofactor,

pyridoxal phosphate Pyridoxal phosphate (PLP, pyridoxal 5'-phosphate, P5P), the active form of vitamin B6, is a coenzyme in a variety of enzymatic reactions. The International Union of Biochemistry and Molecular Biology has catalogued more than 140 PLP-dependent a ...

References

* * * * * * EC 2.5.1 Pyridoxal phosphate enzymes Enzymes of unknown structure {{2.5-enzyme-stub