The use of long wavelength fluorescence in the study of ligand-protein interactions
The binding of a drug or other ligand to plasma proteins can effect their absorption, metabolism and excretion which can lead to a change in its toxicity and therapeutic action. Fluorescence is a technique that has been used to study such interactions and has the advantages of extreme sensitivity and specificity. Previously fluorescence has been monitored in the UV /vis range of the spectrum. However, a new development is long wavelength fluorescence (600-1000nm), which has the added benefits of a lower background, decreased scattering, decreased photodecomposition and the availability of inexpensive, solid state, optical components. Certain dyes including polymethines, xanthenes and phenoxazines that fluoresce in the long wavelength region (600-1000nm) of the spectrum were investigated for use as fluorescence probes. Nile Red, a strongly hydrophobic phenoxazine dye, was found to have an emission wavelength and intensity which was strongly dependent on the polarity of its environment. Consequently, it was bound to certain proteins including bovine and human serum albumin, aI-acid glycoprotein and B-lactoglobulin and provided both qualitative and quantitative information on the nature and type of binding site on the protein. It was also used in the study of ligand protein binding interactions in which competition for a binding site on the protein occurs between the probe and other ligands such as drugs or fatty acids. The project also involved a preliminary investigation into a novel double probe technique for the study of drug-protein interactions and the development of a flow injection analysis method involving gradient titration of a drug against a probe:protein system.