Chemistry. The motions of an enzyme soloist.

Dynamics of proteins are crucial to their function. In his Perspective, Orrit stresses the advantages of studying these dynamics with single-molecule methods--which require no synchronization--rather than with conventional ensemble measurements. He highlights the report by Yang et al., who follow the fluorescence of a single enzyme molecule. Electron transfer from the fluorophore to a quencher induces fluctuations of the fluorescence lifetime along with the fluorophore-quencher distance. The wide range of characteristic times of those fluctuations reveals the complexity of the protein's potential energy landscape. As a new molecular ruler, electron transfer complements other single-molecule methods such as energy transfer (FRET) for distances shorter than a few nanometers.