Phosphorescence Probe of Heme Protein Dynamics

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A detailed understanding of the dynamic internal motion of globular proteins is of fundamental importance to a knowledge of the structure/function relationships of proteins. Dr. Schuh has recently discovered that quenching of the phosphorescence of 6-bromo-2-naphthyl sulfate by the heme of heme proteins can be used to assess transient openings in cytochrome c and myoglobin. The rate constant for quenching, kq, is determined from lifetime measurements of laser-induced phosphorescence and is used to estimate the extent to which motion of heme proteins makes the prosthetic heme rings accessible. If 1-bromopyrene, bromoanthracenes, 9-bromophenanthrenes, and eosin, are found to be suitable phosphorescent probes, it is proposed that the correlation of kq with the size of the molecular probe be used to estimate the size of transient openings in the heme proteins myoglobin, hemoglobin, cytochromes c and cytochrome c peroxidase. The ultimate goals are to: 1) estimate the size of transient fluctuations in proteins, 2) determine whether accessibility of the heme ring in redox proteins is important for the flow of electrons in and out of the proteins, and 3) determine the importance of transient changes in tertiary structure of the oligomers of hemoglobin during the binding and release of dioxygen molecules. The achievement of these goals will improve our understanding of structure/function relationships in proteins.