Factor I:MCP, CR1:C4b, C3b complexes Complement factor I MCP, CR1 Factor I inactivates MCP/CR1-bound C4b/C3b Authored: Jupe, S, 2010-10-26 EC Number: 3.4.21 Edited: Jupe, S, 2010-11-01 Factor I cleaves the truncated alpha (a') chain of C4b between Arg-1336 and Asn-1337 and then again between Arg-956 and Thr-957, producing a 16 kDa fragment known as alpha4, derived from the C terminus of the a' chain, followed by a 27 kDa alpha3 fragment. The remaining alpha 2 (C4d) fragment stays covalently bound to the cell membrane while the complex of disulfide-linked alpha3, alpha4, beta chain and gamma chain are released (C4c) into the fluid phase (Fujita et al. 1978). Pubmed1386357 Pubmed3295051 Pubmed6214588 Pubmed702059 Pubmed7391570 Reactome Database ID Release 43977615 Reactome, http://www.reactome.org ReactomeREACT_118673 Reviewed: Bradley, DT, 2012-02-13 Reviewed: Fraczek, LA, 2012-02-13 has a Stoichiometric coefficient of 2 C4c, C3f C4d, iC3b