C2 is cleaved into the large C2a and the small C2b fragment. This irreversible, extracellular reaction can be catalyzed by activated MBL, generated through the lectin pathway of complement activation (Vorup-Jensen et al. 2000), and by activated C1, generated through the classical pathway (Nasagawa and Stroud 1977). N.B. Early literature refers to the larger fragment of C2 as C2a. However, complement scientists decided that the smaller of all C fragments should be designated with an 'a', the larger with a 'b', changing the nomenclature for C2. For this reason recent literature may refer to the larger C2 fragment as C2b, and the classical C3 convertase as C4bC2b. Throughout this pathway, Reactome uses the current (Feb 2012) Uniprot names which adhere to the original naming practice.
Petersen, SV, Davis, SJ, Sim, RB, Schwaeble, W, Jensenius, JC, Thiel, S, Poulsen, K, Reid, KB, Hansen, AG, Vorup-Jensen, T
Calcott, MA, Polley, MJ, Muller-Eberhard, HJ
Stroud, RM, Nagasawa, S
Sim, RB, Moffatt, BE, Gal, P, Hajela, S, Hajela, K, Wong, KH, Ferluga, J, Kojima, M, Ambrus, G
serine-type endopeptidase activity of C4 activators [plasma membrane]
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