EC - Alternative-complement-pathway C3/C5 convertase

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IntEnz Enzyme Nomenclature


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



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

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , MEROPS , UniPathway
Protein domains and families: PROSITE:PDOC00124
Structural data: CSA , EC2PDB
Gene Ontology: GO:0003812
CAS Registry Number: 80295-67-6


  1. Kerr, M.A.
    Human factor B.
    Methods Enzymol. 80C: 102-112 (1981). [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: 153-157 (1984). [PMID: 6323161]
  3. Müller-Eberhard, H.J.
    The second component of human complement.
    Annu. Rev. Biochem. 57: 321-347 (1988). [PMID: 3052276]

[EC created 1981]