Catalytic activity:Cleavage of Arg-|-Ser bond in complement component C3 alpha-chain to yield C3a and C3b, and Arg-|-Xaa bond in complement component C5 alpha-chain to yield C5a and C5b.,Function:Factor B which is part of the alternate pathway of the complement system is cleaved by factor D into 2 fragments: Ba and Bb. Bb, a serine protease, then combines with complement factor 3b to generate the C3 or C5 convertase. It has also been implicated in proliferation and differentiation of preactivated B-lymphocytes, rapid spreading of peripheral blood monocytes, stimulation of lymphocyte blastogenesis and lysis of erythrocytes. Ba inhibits the proliferation of preactivated B-lymphocytes.,polymorphism:Two major variants, F and S, and 2 minor variants, as well as at least 14 very rare variants, have been identified. The variants His-9 and Gln-32 are associated with a reduced risk of age-related macular degeneration (ARMD) [MIM:603075]. ARMD is a multifactorial eye disease and the most common cause of irreversible vision loss in the developed world.,similarity:Belongs to the peptidase S1 family.,similarity:Contains 1 peptidase S1 domain.,similarity:Contains 1 VWFA domain.,similarity:Contains 3 Sushi (CCP/SCR) domains.,subunit:Monomer.,
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