Energy Transfer and Fluorescence Quenching in Complexes of Polymethine Dyes with Human Serum Albumin^¶

Abstract

Electronic excitation energy transfer (EET) between molecules of polymethine dyes bound to human serum albumin (HSA) has been established and studied by absorption and fluorescence spectroscopy as well as by fluorescence decay measurements. In this system, excitation of the donor dye molecule leads to fluorescence of the acceptor dye molecule, both bound to HSA, with donor fluorescence quenching by the acceptor. The short distance between the donor and the acceptor (25‐28 Å) revealed from the Förster model of EET as well as some spectroscopic data show that both molecules are probably located in the same binding domain of HSA. The role of HSA is to bring donor and acceptor molecules together to a distance adequate to achieve EET as well as to increase the donor and acceptor fluorescence quantum yields. Efficient quenching of the intrinsic HSA fluorescence by some polymethine dyes (oxonols) is observed. The experimental results fit well a model for the formation of a weakly fluorescent dye‐HSA complex; the quencher in this complex should be located in the immediate vicinity of the HSA fluorophore group (Trp214).

Spectroscopic investigations to reveal the nature of interactions between the haem protein myoglobin and the dye rhodamine 6G

“…Protein residues (such as tryptophan) could be involved in energy transfer reactions with certain dye molecules . Using this property, it may be possible in the near future to develop electronic energy transfer‐based biosensors for the detection of alterations at the conformational states of the biomolecules upon binding to other molecules .…”