A Second Component in Bovine AA Amyloid Fibrils Not Identical with Protein AA Is Essential for AA Amyloid Fibrillogenesis

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Abstract
Amyloid fibrils were isolated from the renal papillae and glomeruli of cows with spontaneous AA amyloidosis. The fibrils were solubilized by treatment with guanidine hydrochloride (Gu HCl) and subjected to gel filtration on Sephacryl S-200. Two other fractions were obtained beside the void volume and the AA fractions. Reaggregation studies were performed by dialyzing the fractions, separately or incombinations, against Gu-HCl-free solutions. Protein AA alone (.apprx. 10 kd [kilodalthon]) appeared not to precipitate. The other fractions alone and the combinations of fractions tested formed precipitates. The precipitates containing all fractions (including protein AA) or protein AA plus a fraction containing a 19- and 23-kd protein revealed congophilic green birefringent fibrillar material. Dialysis against acidic and Ca-containing solutions gave the best results. Amyloid fibril-like material was visible on EM examination. The amino acid composition of the 19 + 23-kd material appeared to be slightly different from protein AA and evidently unlike SAP. On immunofluorescence-absorbance studies the 19 + 23-kd material appeared evidently unlike protein AA and SAP. From the findings it is concluded that for spontaneous formation of AA amyloid fibrils other non-AA proteins are necessary.