In Vitro Production of an Amyloid-Like Substance from γ₃Heavy Chain Disease Protein

Zu protein, a γ3-heavy chain disease protein isolated from the urine of a patient with γ-heavy chain disease and amyloidosis, was digested with pepsin in pH 3.5 buffer at 37d`C. The precipitate which formed was Congo red positive and exhibited green birefringence in polarized light. Electron microscopy, by negative staining, revealed fibrils with dimensions 70-80 Å x 850 - 1950 Å. These findings were consistent with those obtained from amyloid fibrils derived from pepsin digestion of certain Bence Jones proteins. The X-ray diffraction pattern of the dried precipitate yielded two rings. The outer ring corresponded to a spacing of approximately 4.7 Å, and the inner ring corresponded to a spacing of approximately 10.6 Å. These dimensions are consistent with β-pleated sheet structure. The mildly reduced and alkylated Zu precipitate demonstrated an approximate molecular weight of 8000 daltons on SDS polyacrylamide gel electrophoresis. Automatic amino-terminal sequence analyses of the mildly reduced and alkylated Zu precipitate suggested that the polypeptide chain was blocked. It seems reasonable to assume that Zu γ3-heavy chain disease protein was related to the widespread amyloidosis found in this patient.