DL-Cystathionine is an intermediate in the synthesis of cysteine that is produced from homocysteine and serine by the action of cystathionine-β-synthase (CBS). CBS can also mediate the condensation of cysteine with homocysteine to produce cystathionine and hydrogen sulfide. An excess of cystathionine in the urine, resulting from a congenital deficiency of cystathionase or an acquired deficiency of vitamin B6, is a hallmark of cystathioninuria.
