Figure. . . Western blot analysis of proteinase K (PK) digested brain stem samples with increasing concentrations of PK (relative to concentration used in the Prionics Check WESTERN (Prionics, Zurich, Switzerland). C, kit control, normal bovine brain homogenate; BSE, bovine spongiform encephalopathy sample from cow from Switzerland; unusual samples 1 and 2 and normal sample are from New Zealand cattle and had been confirmed as negative by several test methods (see text). Unusual samples 1 and 2 show a higher concentration of a truncated fragment of the normal prion protein, which was completely digested at increased PK concentrations. It is typical for this fragment that bands are identical in size to lower bands of the normal prion protein in the undigested samples of normal brain homogenates (black arrowheads). White arrowheads show major bands of PK-digested BSE prion protein.