Resonance Energy Transfer

Abstract

One way that an excited molecule can return to the ground state is to transfer the excitation energy to another molecule. This process, resonance energy transfer, plays a particularly important role in photosynthetic organisms. Extended arrays of pigment–protein complexes in the membranes of plants and photosynthetic bacteria absorb sunlight and transfer energy to the reaction centers, where the energy is trapped in electron-transfer reactions (van Amerongen et al. 2000; Green and Parson 2003). In other organisms, photolyases, which use the energy of blue light to repair UV damage in DNA, contain a pterin or a deazaflavin that transfers energy efficiently to a flavin radical in the active site (Sancar 2003). A similar antenna has been found in cryptochromes, which appear to play a role in circadian rhythms (Saxena et al. 2005). Because the rate of resonance energy transfer depends on the distance between the energy donor and acceptor, the process also is used experimentally to probe intermolecular distances in biophysical systems (van der Meer et al. 1994). Typical applications are to measure the distance between two proteins in a multienzyme complex or between ligands bound at two sites on a protein, or to examine the rate at which components from two membrane vesicles mingle in a fused vesicle. An inquiry into the mechanism of resonance energy transfer also provides a springboard for discussing other time-dependent processes such as electron transfer.