Events

Proton-coupled electron transfer (PCET) reactions play a vital role in a wide range of biological processes. This talk will summarize the main concepts from our PCET theory and will present applications to enzymes and photoreceptor proteins. Our general theoretical formulation for PCET includes the quantum mechanical effects of the electrons and transferring protons, as well as the motions of the donor-acceptor modes and solvent or protein environment. This PCET theory enables the calculation of rate constants and kinetic isotope effects for comparison to experiment and the study of nonequilibrium dynamics. Our application of this theory to PCET in soybean lipoxygenase provides an explanation for the unusually large kinetic isotope effects in terms of hydrogen tunnelling in a constrained enzyme environment. A more recent application explores the PCET pathway for the enzyme ribonucleotide reductase (RNR), which is essential for DNA synthesis and entails six PCET reactions spanning more than 32 Angstroms across an aqueous interface. Another application focuses on blue light using flavin (BLUF) photoreceptor proteins, which are critical for the light regulation of many physiologically important processes. In these proteins, photoexcitation to a locally excited state within the flavin instigates electron transfer from a tyrosine to the flavin, followed by proton transfer from this tyrosine to the flavin and then a reverse PCET that produces the light-adapted signaling state. Our theoretical studies highlight the importance of hydrogen tunneling, excited vibronic states, reorganization, electrostatics, and conformational motions in biological processes.

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