Isolation and characterization of rainbow trout (Oncorhynchus mykiss) serum amyloid P component (SAP)

We purified a Ca(2+)-dependent agarose-binding protein from rainbow trout (Oncorhynchus mykiss) sera. SDS-PAGE analysis showed the possibility that the purified protein was a polymer with a molecular weight of over 100,000 composed of covalently-bounded 32-kDa subunits. N-terminal twenty amino acid sequence of the 32-kDa protein showed partial homology with other known serum amyloid P components (SAPs) including plaice (Pleuronectes platessa) (indicated 40% homology), human (55%), hamster (45%), rat and mouse (40%) SAPs. In electron micrographs the 32-kDa protein was observed as pentameric disc-like structure. On the basis of the results, the 32-kDa agarose-binding protein of rainbow trout was concluded to belong to pentraxin family and to be a SAP homologue.