IUBMB Enzyme Nomenclature


Accepted name: complement factor I

Reaction: Inactivates complement subcomponents C3b, iC3b and C4b by proteolytic cleavage

Other names: complement component C3b inactivator; C3b inactivator; C3b/C4b inactivator; C3bINA; complement C3b/C4b inactivator; complement C4b inactivator; conglutinogen-activating factor C; complement C3b inactivator; factor I; complement C4bi

Comments: Cleavage of complement subcomponent C3b requires its binding to cofactor factor H or complement receptor CR1; cleavage of iC3b requires complement receptor CR1; cleavage of C4b requires C4b-binding protein. In peptidase family S1 (trypsin family)

Links to other databases: BRENDA, EXPASY, KEGG, MEROPS, Metacyc, PDB, CAS registry number: 80295-66-5


1. Nagasawa, S., Ichihara, C. and Stroud, R.M. Cleavage of C4b by C3b inactivator: production of a nicked form from C4b, C4b', as an intermediate cleavage product of C4b by C3b inactivator. J. Immunol. 125 (1980) 578-582. [PMID: 7391570]

2. Crossley, L.G. C3b inactivator and β1H. Methods Enzymol. 80 (1981) 112-124. [PMID: 6210825]

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

[EC created 1981]

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