The amino acid sequence of duck amyloid A (AA) protein

AA protein constitutes 50 to 60% of the amyloid fibrils from livers of ducks developing spontaneous amyloidosis and has a m.w. of about 12,000. The sequence of the first 73 residues was established by automatic Edman degradation of the whole molecule and isolated cyanogen bromide fragments, and corroborated by placement of tryptic peptides. The sequence from position 76-80 was tentatively derived from a peptide that was homologous to that region of human and monkey AA proteins. Carboxypeptidase digestion showed the carboxy terminal sequence to be Ala, Arg, with some heterogeneity (Ser, Arg). Compared to human AA protein, there were five additional residues at the amino terminus. In view of the m.w. and the existence of additional peptides an extension at the C-terminal end seems likely. Sequence homologies to other AA proteins are discussed.