Phosphorus-31 nuclear magnetic resonance spectroscopy reveals two conformational forms of chloroacetol phosphate-bound triosephosphate isomerase.

Chloroacetol phosphate covalently reacts with Glu-165 in the catalytic center of triosephosphate isomerase. Reaction of the enzyme with the substrate analogue results in two 31P resonances at 6.8 and 5.5 ppm. Dissociation with guanidinium chloride results in a single resonance at 4.5 ppm. Reassociation and redimerization of the triosephosphate isomerase-chloroacetol phosphate complex restores only the resonance at 5.5 ppm. The two 31P resonances appear to represent different conformations of the enzyme which are trapped upon reaction with the affinity label.