Identification and characterization of amyloid protein AA in spontaneous canine amyloidosis

Amyloid fibrils were isolated from kidney tissue of a dog that presented with renal failure due to spontaneous amyloidosis. This fibril material was reduced, alkylated and chromatographed on a column of Sepharose CL6B. A major retarded fraction, when subjected to amino acid sequencing, demonstrated a blocked amino terminus. The isolated protein was then degraded with cyanogen bromide, and the resultant three peptides were isolated by high-pressure liquid chromatography. The amino acid sequence of one peptide corresponded to the sequence of human amyloid protein AA from position 17 to 23. A second peptide gave an amino acid sequence homologous to the published human protein AA sequence starting with position 24. Although a high degree of homology between canine and human AA is seen, the blocked amino terminus is similar to the AA protein of mink. These data show that spontaneous canine amyloid is analogous to human reactive (secondary) amyloid and, therefore, may aid in defining mechanisms of human amyloid pathogenesis.