Myoglobin, a paradigm in the study of protein dynamics.

More than 40 years have passed since Kendrew determined the structure of sperm whale myoglobin. It gave us the first insight into the impressive architecture of an alpha helical protein folded via loops into a well ordered, nearly spherical molecule. As time progressed, thousands of new protein structures were published with increasing resolution. The myoglobin structure was also continuously improved and, three years ago, a resolution of 0.9 A was achieved. A wide variety of spectroscopic techniques have been applied to study the dynamics of this molecule and the electronic properties of the heme iron atom. Even nowadays, experiments on myoglobin are still of great interest for a number of reasons: Physical research cannot go into all details in a large number of systems. In semiconductor physics, most concepts were developed by investigating germanium and silicon and were subsequently used to understand more complicated semiconductor systems; myoglobin plays a similar role in molecular biophysics. Concepts like "energy landscape", "conformational substates", "dynamic transition", or "protein-specific motions" should be of general relevance for understanding the physics of biological macromolecules. In biology, functionally important processes often occur at conditions and time scales where physical experiments are extremely difficult and yield ambiguous results. Going to low temperatures often allows one to separate the different dynamic processes. Another helpful tool is molecular engineering. Specific alterations in the sequence of the protein open the possibility to modify reaction rates and to retard the kinetics.