Keywords: Cysteine biosynthesis unlabeled.svg Diagram showing the biosynthesis of cysteine Homocysteine top left and serine top right are reacted to form cystathionine middle which is next converted to alpha-ketobutyric acid α-ketobutyrate bottom left and cysteine bottom right Own 12 46 25 March 2016 UTC Ed Edgar181 Cysteine Biosyntheses Homocysteine serine Cystathionine |