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, cysteine dioxygenase, and sulfinoalanine decarboxylase to produce hypotaurine and then taurine.
Alternately, the cysteine from the cystathionine gamma-lyase can be used by the enzymes glutamate–cysteine ligase and glutathione synthetase to produce glutathione.
An excess of cystathionine in the urine is called cystathioninuria.
Biosynthetically, cystathionine is generated from homocysteine and serine by cystathionine beta synthase. It is then cleaved into cysteine and α-ketobutyrate by cystathionine gamma-lyase.
catalyzes the upper reaction and cystathionine gamma-lyase catalyzes the lower reaction.
