Isolation of a carp complement protein homologous to mammalian factor D

Factor D of carp (Cyprinus carpio) complement was purified to apparent homogeneity by a 4-step chromatographic procedure and examined for physicochemical and functional properties. Carp factor D proved to be an alpha-globulin with a molecular mass of 29 kDa and the serum concentration was estimated to be 6 micrograms/ml. The NH2-terminal amino acid sequence (30 residues including five unidentified positions) of carp factor D showed high homologies (57-60%) to those of mammalian factor D. Neither functional compatibility nor common antigenicity was observed between carp and human factor D. This report is apparently the first description on the factor D molecule in a non-mammalian species.