E1 bound ubiquitin E1 mediated ubiquitin activation Authored: Garapati, P V, 2010-10-29 EC Number: 6.3.2.19 Edited: Garapati, P V, 2010-10-29 Pubmed16595681 Pubmed18662542 Pubmed19352404 Reactome Database ID Release 43983153 Reactome, http://www.reactome.org ReactomeREACT_75782 Reviewed: Elliott, T, 2011-02-10 Ubiquitin is activated in an ATP-dependent manner, catalyzed by E1 ubiquitin-activating enzymes. In the first step of ubiquitin activation, the E1 enzyme binds ATP, Mg+2 and ubiquitin, and catalyses ubiquitin C-terminal acyl-adenylation (Ubiquitin-AMP). In the second step, the catalytic cystine in the E1 attacks the ubiquitin-adenylate (Ub-AMP) to form the activated ubiquitin-E1 thioester-bonded complex and an AMP leaving group. The intermediate reaction involving the formation of the ubiquitin-AMP complex is not represented here. ubiquitin Activating enzymes E1