Complement C3b: Proteins and Enzymes

C3 is a key component of the complement system since classical and alternative activation pathways merge at the C3 activation step when C3 is split into C3a and C3b. The molecular mass of C3 is 185 kDa and it consists of alpha and beta chains (110 kDa and 75 kDa respectively) held together by disulfide bonds (1,2).