Interpretation of thermal perturbation spectra of proteins.

The thermal perturbation difference spectrum of reduced lysozyme has a long wave length extremum at 304 nm at pH 6.15 and a very small extremum at 306 nm at pH 1.5. These results differ from those of Leach & Smith (1972), which showed an extremum at 293 nm, the same as for model tryptophyl compounds. Our result may arise from a conformational difference between the two sample temperatures. The interpretation of thermal perturbation spectra of proteins is discussed. Contributions from thermally induced concentration differences, buried chromophores, and chromophores in crevices are considered in the interpretation of the thermal perturbation spectrum of bovine serum albumin. It is suggested that chromophores in pauci-aqueous crevices may appear buried toward thermal perturbation spectroscopy but accessible toward solvent perturbation and chemical reagents.