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Reactions reveal enzyme motions Conformational dynamics of biological molecules play a role in their biological function, but such dynamics can be difficult to probe using ensemble-averaged experiments. Harvard chemistry professor X. Sunney Xie and coworkers, including Haw Yang and Guobin Luo, use single-molecule photoinduced electron-transfer reactions to probe the conformational dynamics of the enzyme flavin reductase [Science, 302, 262 (2003)]. A tyrosine residue located less than 5 Å from the substrate quenches the fluorescence of the flavin substrate in a distance-dependent manner. By monitoring the natural fluorescence of the flavin photon by photon, the team can observe angstrom-scale fluctuations in the protein conformation. The electron-transfer method is complementary to fluorescence resonance energy transfer, another technique that is sensitive to nanometer-scale motions and often requires the addition of bulky donor and acceptor dye molecules. The researchers find that conformational changes occur over a wide range of time frames, including the timescale at which catalysis occurs, so conformational fluctuations may help explain fluctuations in the rate of enzyme catalysis. |
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