Fig. 1
Long-term proteinase K sensitivity of PrPSc derived from different scrapie and BSE strains (A) or field isolates (B). To investigate the sensitivity of scrapie and BSE strains, isolates to proteinase K prion rods were purified from mouse brain homogenate pools (a minimum of four mice per trial) by differential centrifugation. Fractions containing PrPSc were standardized according to their protein concentrations and signal intensities. Aliquots were subsequently exposed to 50 µg/ml (final concentration) proteinase K for 1, 3, 6, 24, or 48 hr at 37°C. Residual PrPSc was then visualized by immunoblot and total band signals quantified by the photoimager technique. Residual PrPSc antigen signals were calculated as arithmetic means from a minimum of two extraction and digestion experiments per strain. Each sample taken was analyzed on at least four different immunoblots. Combined PrPSc signals (non-, mono- and diglycosylated bands) obtained after 1 hr of proteolysis were set at 100% to minimize artefacts because of the possible initial contamination of fibrils with other proteins. Standard error values are indicated.