Factor I Protein

Purified human complement component Factor I. Factor I is a fluid phase complement regulatory enzyme. It consists of two peptide chains with molecular weights of 50 kD and 38 kD, respectively. Factor I is present in plasma at 35 mg/L. With Factor H, CR1 or C4 Binding Protein acting as a cofactor, Factor I cleaves the C3b subunit of the alternative and classical pathway convertases, thereby inactivating them.