Protein dynamics, tunneling, and all that

We review some physical issues in the theory of reaction rates in proteins, starting with the classic observations of DeVault and Chance on “electron tunneling” in bacterial photosynthesis and their interpretation by Hopfield. These ideas lead to a family of generalized spin-boson models for reaction rates, and these models are used to explore the significance of quantum effects and the possibility of “dynamical specificity” extreme sensitivity of the rate to changes in protein dynamics. We assess the success of these models in rationalizing kinetic and spectroscopic data both on photosynthetic electron transfer and on ligand binding to heme proteins, and conclude with some open questions.