Primary structure of duck amyloid protein A. The form deposited in tissues may be identical to its serum precursor

The amino acid sequence has been determined for the major protein that accumulates in amyloid fibrils in tissues of the Pekin duck. With the exception of 16 residues at the amino terminus, this 106-residue protein is homologous with human serum amyloid protein A (104-residue apoSAA), which is the putative precursor of the 76-residue protein that accumulates in human patients with amyloidosis. Duck serum is shown to contain a protein that is immunologically related and approximately equal in size (12 kDa) to the deposited form in ducks. These results indicate that proteolytic processing of the precursor is not a necessary step in the deposition of amyloid fibrils, at least in the duck.