Isolation of a low-molecular-weight serum component antigenically related to an amyloid fibril protein of unknown origin.

An amyloid fibril protein of unknown origin from a patient with systemic amyloidosis has been purified to homogeneous charge and size by gel filtration and two step isoelectric focusing. From crude antisera to the initial heterogeneous fibril protein, monospecific antibodies have been obtained by immunoabsorption with the immobilized purified amyloid protein. These antibodies have been used to identify an antigenically related serum component in whole sera of patients with and without amyloidosis. Chromatography on Sephadex G-200 in phosphate buffered saline of a patient's whole serum yields a component with an apparent molecular weight of approximately 200,000. Guanidine denaturation of this high-molecular-weight serum component followed by Sephadex G-100 column chromatography in 5 M guanidine affords an antigenically reactive protein with an apparent molecular weight of about 12,500. The antigenic similarity and molecular weight of the latter protein indicates that it could act as the smallest serum precursor of the tissue fibril protein in this group of cases of amyloidosis.