Cysteine is degraded to serine and H2S Authored: Stephan, R, 2010-10-24 EC Number: 4.4.1.1 Edited: Jassal, B, 2011-09-29 Pubmed10212249 Pubmed19261609 Reactome Database ID Release 431614614 Reactome, http://www.reactome.org ReactomeREACT_115816 Reviewed: D'Eustachio, P, 2011-10-13 alpha,beta-elimination activity of cystathionine-gamma-lyase (CTH) replaces the sulfur in cysteine with oxygen from water, resulting in serine and toxic hydrogen sulfide, which is further oxidized in mitochondria (Chiku et al. 2009, Steegborn et al. 1999).