Primary structure of amyloid fibril protein AA in azocasein-induced amyloidosis of CBA/J mice.

Secondary amyloidosis was induced in CBA/J mice by subcutaneous injections of azocasein after priming with amyloid-enhancing factor. Amyloid fibrils were isolated from spleens and the subunit amyloid A (AA) protein purified by gel filtration on a column of Sepharose CL6B. The AA protein was fragmented with trypsin, cyanogen bromide, and Staphylococcus protease, and the peptides were purified by reverse-phase high-performance liquid chromatography. This protein is composed of 73 amino acid residues arranged in a single polypeptide chain with homogeneous amino and carboxyl terminals. Sequence homology with protein AA from other species is quite high with near identity for residues 31 through 54. This sequence is identical to the partial structures for CBA/J mouse AA and serum amyloid A (SAA) previously reported. It is also an exact match to a predicted 73-residue segment from one form of mouse SAA complementary DNA.