Cleavage of C3 by C3 convertases Activation of C5 Formation of classic C5 convertase PathwayStep6835 PathwayStep6836 PathwayStep6837 Activation of C3 and C5 Authored: de Bono, B, 2004-08-04 09:17:50 Edited: Jupe, S, 2010-11-17 GENE ONTOLOGYGO:0006956 Pubmed15199963 Pubmed458145 Reactome Database ID Release 43174577 Reactome, http://www.reactome.org ReactomeREACT_7972 Reviewed: D'Eustachio, P, 2006-07-03 21:35:13 The 3 pathways of complement activation converge on the cleavage of C3 by C3 convertases. C3 convertase cleaves C3 into C3a and C3b - a central step of complement activation. C3a remains in the fluid phase and acts as an anaphylatoxin, whereas C3b can bind to C3 convertases to form C5 convertase, can act as an opsonin, or is degraded into fragments which cannot form an active convertase.