Comparison of solid and solution state protein structures. Photoacoustic study of solid state bovine methemoglobin...

In an effort to examine the consequences of phase state changes on protein structures, optical absorption spectra of several bovine hemoglobin derivatives in lyophilized, ammonium sulfate-precipitated, and crystalline states were examined. Absorption spectra were used to compare protein conformations. Differences between solution and several solid state spectra were apparent. They were greatest for lyophilized preparations, were inhibited by ligand binding, the tightest binding ligand being the most effective inhibitor, and were substantially or totally reversible upon dissolving the solid state protein. Though the magnitude of spectral changes varied, they all indicated characteristically different proportions of the protein were converted to a reversible hemichrome in each type of solid state preparation. The extent of hemichrome formation was correlated with the degree to which the protein tends to be dehydrated in each solid state preparation. This may reflect the role of water in determining the three-dimensional structure of hemoglobin. Absorption spectra of solid state hemoglobin preparations were obtained from photoacoustic spectra using a novel method for spectral analysis. Results presented here demonstrate the utility of this procedure in probing structures of solid state proteins.