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In enzymology, a cysteine synthase (EC 2.5.1.47) is an enzyme that catalyzes the chemical reaction. O 3-acetyl-L-serine + hydrogen sulfide L-cysteine + acetate. Thus, the two substrates of this enzyme are O 3-acetyl-L-serine and hydrogen sulfide, whereas its two products are L-cysteine and acetate.
A number of pyridoxal-dependent enzymes involved in the metabolism of cysteine, homocysteine and methionine have been shown to be evolutionary related. [1] These enzymes are tetrameric proteins of about 400 amino-acid residues. Each monomer has an active site, which however requires the N-terminal of another monomer to be completed (salt ...
The enzyme cystathionine gamma-lyase converts the cystathionine into cysteine and alpha-ketobutyrate. In plants and bacteria, cysteine biosynthesis also starts from serine, which is converted to O-acetylserine by the enzyme serine transacetylase. The enzyme cysteine synthase, using sulfide sources, converts this ester into cysteine, releasing ...
There are five different structurally related types of PLP enzymes. Members of this family belong to the type I and are: [6] in the transsulfurylation route for methionine biosynthesis: Cystathionine γ-synthase (metB) which joins an activated homoserine ester (acetyl or succinyl) with cysteine to form cystathionine
Other members include cystathionine γ synthase, cystathionine β lyase, and methionine γ lyase. [8] It is also a member of the broader aspartate aminotransferase family. [1] [8] Like many other PLP-dependent enzymes, cystathionine γ-lyase is a tetramer with D2 symmetry. [8] Pyridoxal phosphate is bound in the active site by Lys 212. [2]
The systematic name of this enzyme class is L-cystathionine L-homocysteine-lyase (deaminating; pyruvate-forming). This enzyme participates in 5 metabolic pathways: methionine metabolism, cysteine metabolism, selenoamino acid metabolism, nitrogen metabolism, and sulfur metabolism.
L-cysteine production pathways; Reactants → Enzyme Cofactors Notes O-acetyl-L-serine/hydrogen sulfide → cysteine synthase [9] pyridoxal phosphate not present in humans L-cystine/2 glutathione → glutathione-cystine transhydrogenase [10] cystathionine: → cystathionine γ-lyase [4] pyridoxal phosphate 3-mercapto-pyruvate: → cysteine ...
The plant glutamate cysteine ligase is a redox-sensitive homodimeric enzyme, conserved in the plant kingdom. [26] In an oxidizing environment, intermolecular disulfide bridges are formed and the enzyme switches to the dimeric active state. The midpoint potential of the critical cysteine pair is -318 mV.