Understanding the dynamic internal motion of globular proteins is a problem of fundamental importance to biochemistry. However, it is difficult to follow and gauge the extent of such internal motion of proteins in solution. 2-bromo-6-naphthyl sulfate (BNS) has been found to phosphoresce in degassed aqueous solutions, and the phosphorescence is quenched specifically by the heme rings of heme proteins. By measuring the lifetime of BNS phosphorescence as a function of heme concentration, the rate constant for quenching, k/g, can be determined. Since the quenching of phosphorescence by heme proteins is diffusion controlled, the value of k/q can be used to estimate the extent to which dynamic motion of heme proteins makes the prosthetic heme rings accessible during contact with other molecules. BNS will be used to probe the accessibility of heme rings in myoglobin, cytochrome c, hemoglobin, cytochrome c peroxidase and other heme proteins. In addition to helping to better understand protein dynamics, it is anticipated that the proposed research will also give valuable insights into the functional mechanisms of heme proteins. Some of the most important physiological functions of living systems are performed by heme proteins (e.g. transport of electrons in the production of metabolic energy and transport and storage of O/2 for oxidation of foods). A better understanding of the mechanisms of these proteins will eventually allow the development of ways to control for better health the physiological functions determined by heme proteins. An ultimate long-term objective will be to develop and use BNS as a phosphorescent probe of other specific biological polymers in other solvent environments, such as natural or artificial membranes.
