|Section2= |Section3= }} Cystathionine is an intermediate in the synthesis of cysteine. It is generated from homocysteine and serine by cystathionine beta synthase. It is cleaved into cysteine and α-ketobutyrate by cystathionine gamma-lyase. An excess in the urine is called cystathioninuria.… (More on Cystathionine)