IUBMB Enzyme Nomenclature


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

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

Other names: complement component C3/C5 convertase (alternative); proenzyme factor B; properdin factor B; C3 proactivator; glycine-rich β-glycoprotein; heat-labile factor; C3 convertase; C3b,Bb,CVF,Bb,C5 convertase; (C3b)n,Bb; complement C 3(C 5) convertase (amplification); alternative complement pathway C3(C5) convertase; C5 convertase; CVF,Bb; (CVF)-dependent glycine-rich-beta-glucoprotein; cobra venom factor-dependent C3 convertase

Comments: A bimolecular complex of complement fragment Bb with either C3b or cobra venom factor; Bb contains the active site. Bb is formed by cleavage of proenzyme factor B by factor D. Cleavage of complement component C5 requires additional C3b which binds C5 and renders it susceptible to cleavage by C3b,Bb complex. C3b,Bb is stabilized in plasma by factor P. Complement factor B is In peptidase family S1 (trypsin family)

Links to other databases: BRENDA, EXPASY, KEGG, MEROPS, Metacyc, PDB, CAS registry number: 80295-67-6


1. Kerr, M.A. Human factor B. Methods Enzymol. 80 (1981) 102-112 . [PMID: 7043188]

2. Morley, B.J. and Campbell, R.D. Internal homologies of the Ba fragment from human complement component Factor B, as a class III MHC antigen. EMBO J. 3 (1984) 153-157. [PMID: 6323161]

3. Müller-Eberhard, H.J. The second component of human complement. Annu. Rev. Biochem. 57 (1988) 321-347. [PMID: 3052276]

[EC created 1981]

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