Terminal components of carp complement constituting a membrane attack complex

The membrane attack complex (MAC) of carp complement was extracted with deoxycholate from rabbit erythrocytes lysed by carp serum and purified by a two-step chromatographic procedure. On two-dimensional SDS-PAGE of carp MAC, eight bands were detected. The band of M(r) 91,000 was identified as carp C9 by western blotting using anti-carp C9, and two bands of M(r) 62,000 and one band of M(r) 22,000 were confirmed as those of carp C8 alpha, C8 beta and C8 gamma, respectively, by their N-terminal amino acid sequences. The bands of M(r) 102,000 and 73,000, which generated from a 180,000 band under reducing conditions, were those corresponding to human C5b alpha and C5b beta, respectively. The remaining bands of M(r) 115,000 and 106,000 were identified as those corresponding to human C6 and C7, as determined by their molecular size, single-chain structures and similarities in N-terminal amino acid sequences to their mammalian counterparts. Densitometric scan of the gels showed the molar ratio of C5b, C6, C7, C8 and C9 in carp MAC to be 1:1:1:1:4. Based on these results, it appears that, as with mammals, the cytolytic pathway of bony fish complement is composed of five terminal components from C5 to C9.