a, the purity of PrP was estimated by electrophoresis on precast
12% SDS-PAGE followed by staining with Coomassie Blue. b, CD spectrum
of PrP (0.25 mg/ml) confirmed native α-helical conformation. c,
electrospray ionization mass spectrometry spectrum of PrP collected on a
Waters ZMD single quadrupole mass spectrometer operated in positive ion mode.
The spectrum shows a single series of peaks corresponding to multiply charged
ions confirming high purity of PrP. The labels on the peaks (A21,
A22, etc.) indicate the mass/protonation (charge) ratio of the ion
species. Deconvolution of the electrospray ionization mass spectrometry
spectrum results in a single peak with a maximum of 23102.35 Da
(inset), which is in good agreement with the predicted molecular mass
of 23102.42 Da.