Isolation and characterization of amyloid-related serum protein SAA as a low molecular weight protein.

With direct immunoprecipitation or gel filtration under dissociating conditions, amyloid-related serum protein SAA has been isolated as a low molecular weight protein from the serum of two patients with rheumatoid arthritis but without known amyloidosis. The isolated protein SAA showed antigenic identity and an amino acid composition that was similar, but not identical, with isolated fibril protein AA. Molecular weight estimations suggest that protein SAA is approximately 50% larger than protein AA and has a molecular weight of 14,000-15,000 daltons. Preliminary results indicate that protein SAA from a patient with amyloidosis has a similar small molecular weight subunit.