An unusually large (83 amino acid residues) amyloid fibril protein AA from a patient with Waldenström's macroglobulinaemia and amyloidosis.

The amino acid sequence studies of a human amyloid fibril protein AA derived from a patient with Waldenström's macroglobulinaemia revealed 83 residues. This protein AA was larger than but otherwise very similar to other human AA proteins studied by complete sequencing. Two amino acids were found both in position 52 (Val/Ala) and in position 53 (Trp/Arg), strongly suggesting a polymorphism of AA proteins. Immunologic studies showed the antigenic determinant(s) reacting with antiprotein AA to be located between positions 25 and 76 of the third cyanogen bromide cleavage fragment of the protein.