SPECTRAL HOLE-BURNING AND SELECTION OF CONFORMATIONAL SUBSTATES IN CHROMOPROTEINS

We investigated spectral holes burnt at 1.5 K into the origins of seve ral tautomeric forms of mesoporphyrin IX-substituted horseradish perox idase at pH 8 under pressures up to 2 MPa. From the pressure-induced l ineshift the compressibility of the apoprotein could be determined. We found that the compressibility changed significantly when measured at different tautomer origins. It was concluded that there must be a cor relation between the tautomer configurations of the chromophore and th e actual structures of the apoprotein. As a consequence, specific conf ormational substates of the protein can be selected by optical selecti on of the associated tautomers.