IUBMB Enzyme Nomenclature


Accepted name: classical-complement-pathway C3/C5 convertase

Reaction: Selective cleavage of ArgSer bond in complement component C3 α-chain to form C3a and C3b, and Arg bond in complement component C5 α-chain to form C5a and C5b

Other names: C3 convertase; C; C4b,2a; C5 convertase; C; C4b,2a,3b; C42; C5 convertase; C423; C4b,2a,3b; complement C.hivin.4.hivin2; complement C3 convertase

Comments: A complex of complement fragments C4b, C2a and C2b. C2a contains the active site, C2b the site for C4b binding. C2a and C2b are formed by cleavage of proenzyme C2 by complement subcomponent C. Cleavage of C5 requires complement fragment C3b which binds C5 and renders it susceptible to cleavage by the C4b,2a complex. Includes former EC Complement component C2a is In peptidase family S1 (trypsin family)

Links to other databases: BRENDA, EXPASY, KEGG, MEROPS, Metacyc, PDB, CAS registry number: 56626-15-4


1. Kerr, M.A. The second component of human complement. Methods Enzymol. 80 (1981) 54-64. [PMID: 7043188]

2. Müller-Eberhard, H.J. Molecular organization and function of the complement system. Annu. Rev. Biochem. 57 (1988) 321-347. [PMID: 3052276]

[EC created 1981 (EC created 1981, incorporated 1984)]

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