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. This antibody is specific for an allotypic marker on human C3 (Leu instead of Pro in codon 314 of e, Xenopus/Amphibian,on 9), which occurs regularly in the beta-chain of C3F and occasionally in the beta-chain of C3S (F and S meaning fast and slow migration rate, respectively, on agarose gel electrophoresis). The antibody reacts with the 75-kDa beta-chain band of reduced C3 in immunoblotting , and reacts with the 20-kDa and 17-kDa beta-chain fragments produced by cyanogen bromide cleavage.