Cystathionine

Cystathionine is a non-proteinogenic thioether amino acid that serves as a critical intermediate in the transsulfuration pathway, which converts homocysteine to cysteine (Source: PubChem CID 439156). It is synthesized from homocysteine and serine by the enzyme cystathionine beta-synthase (CBS) and is subsequently hydrolyzed into cysteine and alpha-ketobutyrate by cystathionine gamma-lyase (CTH) (Source: UniProt P35520, P32929). Both enzymes require pyridoxal 5'-phosphate (Vitamin B6) as an essential cofactor for their catalytic activity. In human physiology, cystathionine acts as a metabolic bridge between the methionine cycle and the production of glutathione, the body's primary antioxidant. Abnormal levels of cystathionine are clinically significant; elevated levels in the blood or urine (cystathioninuria) typically indicate a deficiency in cystathionine gamma-lyase or Vitamin B6 (Source: NIH MedlinePlus). Conversely, low levels of cystathionine are a hallmark of classical homocystinuria, a serious metabolic disorder caused by mutations in the CBS gene (Source: StatPearls NBK557508). While cystathionine itself is not a direct therapeutic target for drugs, the enzymes that regulate its concentration are major targets for treating metabolic, cardiovascular, and neurodegenerative diseases. Furthermore, cystathionine serves as a precursor for the production of hydrogen sulfide (H2S), a gaseous signaling molecule involved in vasodilation and cytoprotection. Monitoring cystathionine levels is therefore a vital diagnostic tool for identifying specific inborn errors of sulfur amino acid metabolism.

Other names

L-Cystathionine(2S)-2-amino-4-[[(2S)-2-amino-2-carboxyethyl]sulfanyl]butanoic acidL-allo-Cystathionine

Cystathionine is a metabolic intermediate in the transsulfuration pathway and does not function as a drug target; it serves as the substrate for the enzyme cystathionine gamma-lyase (Source: UniProt P32929).