FIGURE 2.
Reversibility of NaCl-dependent protease resistance of PrPSc. A, PrPSc purified in the presence of 150 mm NaCl was extensively dialyzed (two times) against 20 mm Tris-HCl, pH 7.4, and then submitted to protease digestion with the indicated concentrations of PK for 4 h at 37 °C with 600 rpm agitation. Protease-treated samples were immunoblotted using 3F4 antibody. B, densitometry analysis of the percentage of PrPres (% of PrPres) upon protease digestion. The density of the band intensity was measured and normalized to percentages. Densitometry as a function of PK concentration is shown for PrPSc purified in the presence (triangles) or absence (circles) of 150 mm NaCl (values calculated from Fig. 1B) as well as for the sample in 150 mm NaCl after dialysis (squares). C, PrPSc purified in the absence of salts was supplemented with different concentrations of NaCl (0, 1, 10, 30, 75, 150, 500, and 1000 mm), and samples were submitted to protease digestion at 1000 μg/ml for 4 h at 37 °C with 600 rpm agitation.