FRETting over the Spectroscopic Ruler

Science  29 Mar 2013:
Vol. 339, Issue 6127, pp. 1530-1531
DOI: 10.1126/science.1235761

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An excited fluorescent molecule may not emit light if it can transfer its excitation energy to a nearby molecule. Förster's theory describing electronic excitation energy transfer (EET) (1) is now 65 years old, but it is not ready for retirement. It still enjoys popularity through the FRET (2) method for determining molecular-scale distances. A seminal paper by Stryer and Haugland in 1967 provided experimental support for the predicted inverse sixth power distance dependence of FRET efficiency and coined the term “spectroscopic ruler” (2). Despite the widespread use of fluorescence spectroscopy to determine distances between a “donor” (D) and “acceptor” (A), the method can be tricky, and numerous caveats concerning the FRET model have appeared. On page 1586 of this issue, Consani et al. (3) point out another, based on their use of two-dimensional ultraviolet (UV) transient spectroscopy to disentangle the competing contributions of electron transfer and FRET to the decay of excited tryptophan (Trp) residues in myoglobin (Mb).