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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.
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 ...
In enzymology, a phosphopantothenate—cysteine ligase also known as phosphopantothenoylcysteine synthetase (PPCS) is an enzyme (EC 6.3.2.5) that catalyzes the chemical reaction which constitutes the second of five steps involved in the conversion of pantothenate to Coenzyme A. The reaction is:
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 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.
Cystathionine-β-synthase, also known as CBS, is an enzyme (EC 4.2.1.22) that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway , from homocysteine to cystathionine : [ 5 ]
In enzymology, a 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) is an enzyme that catalyzes the chemical reactions of 3-mercaptopyruvate. This enzyme belongs to the family of transferases, specifically the sulfurtransferases. [1] This enzyme participates in cysteine metabolism. It is encoded by the MPST gene. [2]
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 ...