How quantum chemistry can solve fundamental problems in bioenergetics

Three different enzymes are discussed, cytochrome c oxidase, involved in aerobic respiration, cytochrome c dependent nitric oxide reductase, involved in denitrification (anaerobic respiration), and photosystem II, involved in photosynthesis. For all three systems, free energy profiles for the entire catalytic cycle are obtained from quantum mechanical calculations on large cluster models of the active sites, using hybrid density functional theory with the B3LYP* functional. The free energy profiles are used to solve different fundamental problems concerning energy conservation, enzymatic reaction mechanisms and structure, and also to explain experimental results that seem to be in conflict with each other. Possible future applications to related problems using similar methodology are suggested. © 2015 Wiley Periodicals, Inc.