Search results
Results From The WOW.Com Content Network
Cystathionine is an intermediate in the synthesis of cysteine from homocysteine. It is produced by the transsulfuration pathway and is converted into cysteine by cystathionine gamma-lyase (CTH). Biosynthetically, cystathionine is generated from homocysteine and serine by cystathionine beta synthase (upper reaction in the diagram below).
Reaction 5 is catalyzed by cystathionine beta-synthase while reaction 6 is catalyzed by cystathionine gamma-lyase. The required homocysteine is synthesized from methionine in reactions 1, 2, and 3. The transsulfuration pathway is a metabolic pathway involving the interconversion of cysteine and homocysteine through the intermediate cystathionine.
One of the alternate reactions involving CBS is the condensation of cysteine with homocysteine to form cystathionine and hydrogen sulfide (H 2 S). [13] H 2 S in the brain is produced from L-cysteine by CBS. This alternative metabolic pathway is also dependent on adoMet. [14] CBS enzyme activity is not found in all tissues and cells.
In enzymology, a cystathionine gamma-synthase (EC 2.5.1.48) is an enzyme that catalyzes the formation of cystathionine from cysteine and an activated derivative of homoserine, e.g.: O 4 -succinyl-L-homoserine + L-cysteine {\displaystyle \longrightarrow } L-cystathionine + succinate
Thus, the substrate of this enzyme is L-cystathionine, whereas its 3 products are homocysteine, pyruvate, and ammonia. [2] [3] [4] Found in plants, bacteria, and yeast, cystathionine beta-lyase is an essential part of the methionine biosynthesis pathway as homocysteine can be directly converted into methionine by methionine synthase.
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]
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 ...
Amino acid biosynthesis is the set of biochemical processes (metabolic pathways) by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to synthesize all amino acids. For example, humans can synthesize 11 of the 20 standard amino acids.