A COMPARATIVE PRESSURE TUNING HOLE-BURNING STUDY OF PROTOPORPHYRIN-IXIN MYOGLOBIN AND IN A GLASSY HOST

We measured the behavior of spectral holes under isotropic pressure ch anges as a function of burn frequency. We compared a protein sample, n amely protoporphyrin IX substituted myoglobin in a glycerol/water glas s with a sample where the protoporphyrin IX was directly dissolved in a host glass. The differences are remarkable-holes in the pure glass b ehave as expected for a homogeneous isotropic material. It is the nonl inear frequency dependence of the pressure shift where the deviation o f the protein sample is most obvious. These observations signal a corr elation between the structures of the dye probe and the structures of the apoprotein. They further show that global parameters of the apopro tein, such as the isothermal compressibility, depend strongly on the a ssociated conformational substates and are subject to unexpected large variations.