Myoglobin, a simppe dioxygen-storage protein, is a good laboratory for the investigation of the connection between protein structure, dynamics, and function. Fourier-transform infrared spectroscopy on carbon-monoxymyoglobin (MbCO) shows three major CO bands. These bands are excellent probes for the investigation of the structure-function relationship. They have different CO binding kinetics and their CO dipoles form different angles with respect to the heme normal, implying that MbCO exists in three major conformational substates, A0, A1, and A3. The entropies and enthalpies of these substates depend on temperature above approximately 180 K and are influenced by pH, solvent, and pressure. These results suggest that even a protein as simple as Mb can assume a small number of clearly different structures that perform the same function, but with different rates. Moreover, protein structure and dynamics depend strongly on the interaction of the protein with its environment.
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