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Morphologic, Chemical, and Immunologic Studies of Amyloid-Like Fibrils Formed from Bence Jones Proteins by Proteolysis¹

From the Department of Medicine, New York University Medical Center, School of Medicine, New York 10016

Abstract

Seventy-five Bence Jones Proteins (BJP) were digested with pepsin. Forty-six of 61 and 9 of 14 k-BJP formed precipitates but only 10 of them (9 and 1 ) showed strong congo red uptake, green polarization birefringence, and dichroism. Electron microscopic studies revealed fibrils in eight of which three resembled isolated human amyloid fibrils and five had fibrils atypical for amyloid. Digestion of one BJP with different enzymes resulted in amyloid-like fibrils having different morphologic appearances.

One VI Oz(-) BJP (CAR) was investigated more intensively. Its peptic digest consisted of 70% of an 8000 dalton fragment and 30% of a 12,000 m.w. fragment which were able to form amyloid-like fibrils even after purification. Both appeared to be derived from the variable region by peptide maps. The amino acid sequence of the first 10 residues of the 8000 m.w. fragment placed it in the V region commencing with residue 5.

Tryptic digestion yielded a 13,000 m.w. preamyloid fragment which remained soluble at neutral pH and thus proved suitable for immunologic studies. Studies with antisera to native BJP CAR, the tryptic preamyloid and oxidized BJP CAR indicated that the preamyloid contained idiotypic variable region antigenic determinants which could be revealed either by oxidation or proteolytic digestion of the native precursor BJP. These findings may help to explain the failure of most antisera to native L-chains to react with naturally occurring amyloid proteins.

Footnotes

¹ This work was supported by United States Public Health Service Grants AM-01431, AM-02594, and AM-012274; United States Public Health Service Career Development Award 2-K3-Al-9572; the Health Research Council of the City of New York; the Michael and Helen Schaffer Fund; and the New York Chapter of the Arthritis Foundation, Inc.

Presented in part at the Third Tagung der Gesellschaft für Immunologie, Marburg, 1971 and at the Fourth Tagung der Gesellschaft für Immunologie, Bern, 1972.

² Scholarship of the Deutscher Akademischer Austauschdienst, Bad Godesberg, Germany.

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