Goal of the proposal is the detection and characterization of segmental motions, structural domains and solvent effects on the shape, dimensions, polymerization, and biological functions of soluble and membrane-bound proteins. Segmental motions will be monitored using fluorescence depolarization techniques. The shape and dimension of protein molecules will be inferred from their rotational diffusion and from measurements of energy transfer of fluorescence. The presence of structural domains will be investigated using controlled unfolding processes in denaturing agent-like guanidine hydrochloride, pH and temperature. Removal of prosthetic groups, like heme from hemoglobin, also produce partial unfoldings, which may reveal the presence of structural domains. The proteins to be investigated at the start of the project are hemoglobin and its heme-free derivative, band 3 of the erythrocyte ghosts and calcium dependent ATPase of skeletal sarcoplasmic reticulum. The investigation will increase our understanding of the mechanism that requlate biological transport of gases and ions in fluids and across membranes.