PathwayStep2586 PathwayStep2587 Cysteine formation from homocysteine Authored: Stephan, R, 2010-10-24 Edited: Jassal, B, 2011-09-29 GENE ONTOLOGYGO:0019346 Pubmed15497768 Pubmed20817827 Reactome Database ID Release 431614603 Reactome, http://www.reactome.org ReactomeREACT_115589 Reviewed: D'Eustachio, P, 2011-10-13 Transsulfuration is the interconversion of homocysteine and cysteine, and it fully takes place in bacteria and some plants and fungi. Animals however have only one direction of this bidirectional path, the synthesis of cysteine from homocysteine via cystathionine. Because excess cysteine is degraded to hydrogen sulfide, which is now known as a neuromodulator and smooth muscle relaxant, this pathway is also the main source of its production, which takes place in the cytosol, as well as in extracellular space (Dominy & Stipanuk 2004, Bearden et al. 2010). Cystathionine is formed from homocysteine and serine Cleavage of cystathionine into cysteine