Single molecule enzymology: watching the reaction.

Single molecule optical microscopy can directly monitor substrate turnover by individual enzymes revealing the underlying distribution of reaction rates and enzyme conformations. These techniques are particularly useful for assessing cooperativity in multi-subunit enzymes such as beta-galactosidase, and for directly monitoring how ligand and substrate binding alter dynamic equilibria. Recent investigations of HIV reverse transcriptase have reiterated the importance of single molecule microscopy for determining how proteins move on oligonucleotides and how ligands and inhibitors affect motion. Similar investigations of membrane active enzymes allow direct imaging of protein-membrane interactions. For a large variety of systems, single molecule enzymology provides unprecedented images of how enzymes interact with their substrates and the differences between individual enzymes in a population.