Complement Factor I

**Definition:** A plasma serine proteinase that cleaves the alpha-chains of C3b and C4b in the presence of the cofactors COMPLEMENT FACTOR H and C4-binding protein, respectively. It is a 66-kDa glycoprotein that converts C3b to inactivated C3b (iC3b) followed by the release of two fragments, C3c (150-kDa) and C3dg (41-kDa). It was formerly called KAF, C3bINF, or enzyme 3b inactivator.

**Tree numbers:** - D08.811.277.656.300.760.210 - D08.811.277.656.959.350.210 - D12.776.124.486.274.920.325.210

**Synonyms:** - C3b-C4b Inactivator - C4b-C3b-INA - Complement 3b-Complement 4b Inactivator - C4bC3bINA - Complement C4b-C3b Inactivator - C3b Inactivator