Reduced bovine pancreatic trypsin inhibitor (BPTI) has been shown to be in a compact state [(1988) Biochemistry 27, 8889–8893]. This leads to the proposal that this compact state may be a compact molten globule folding intermediate. Optical rotatory dispersion in the visible region failed to show the presence of pronounced secondary structures in the reduced UPTI and no binding or 8-anilino-1-naphthalenesulphonic acid to reduced BPTI could be detected. Yet, no Cooperative thermal transition was detected by tyrosine fluorescence. These experiments show that reduced BPTI is not in the compact molten globule state.
