Band 3 of the human erythrocyte membrane is a transmembrane protein for which there is strong evidence of involvement in anion trasport. Little is known of the molecular basis of its structure and function. Moreover, because of its lipophilic associations, there is slight chance that its structure and function can be elucidated with techniques such as x-ray diffraction. We propose here to measure the fluorescent response of lipophilic probes, in erythrocyte lipid vesicles whose protein content is almost entirely band 3, to determine the distributon of the tryptophan residues in the hydrophobic region. We will then use energy transfer and lifetime heperogeneity analysis to detect conformational changes induced by anion transport and its inhibitors. Alterations in the membrane lipid structure due to lipid-band 3 protein interactions will also be studied by these methods. A parallel study to characterize the probes in model membranes will be carried out in order to enhance our ability to interpret the results in biological membranes. Here we will be interested in experimentally and theoretically elucidating the dynamic probe-lipid solvent interactions which we have observed in time and temperature dependent emission spectra.