Complement factor 3 iC3 Spontaneous hydrolysis of C3 thioester Authored: de Bono, B, 2004-08-04 09:17:50 Edited: Jupe, S, 2010-11-17 Pubmed6586103 Pubmed6903192 Pubmed6912277 Pubmed6934510 Reactome Database ID Release 43173739 Reactome, http://www.reactome.org ReactomeREACT_8007 The thioester linkage between cysteine residue 1010 and glutamine residue 1013 in the alpha chain of Complement factor 3 (C3) can spontaneously hydrolyze, yielding so-called C3(H2O) (Tack et al. 1980; Pangburn & Muller-Eberhard 1980; Pangburn et al. 1981). Thioester bond hydrolysis causes conformational rearrangements that give C3(H2O) the ability to bind Factor B. The spontaneous hydrolysis rate of C3 under physiological conditions and temperature is about l% per hour, thus the C3b-like properties of C3(H2O) provide a continuous low level initiation of the alternative pathway of complement activation (Pangburn & Muller-Eberhard 1983). If not bound by Factor B, C3(H2O) binds Factor H and is inactivated by Factor I