Photosynthesis

Professor Ralph A. Wheeler
Computational Chemistry Research Group
The University of Oklahoma

Electron Transfer/Photosynthesis Research:

The oxidation/reduction of quinones plays a prominent role in photosynthesis (and respiration). A number of synthetic energy storage systems are designed to model biological electron transfer (ET) by incorporating components of the photosynthetic reaction center, but lack the exquisite control of ET exhibited by the reaction center protein. In preliminary work, we provided the first computational characterization of structures, vibrations, and spin properties of the three quinones most important in biochemistry--ubiquinones, plastoquinones, and menaquinones. We also predicted electron affinities and one-electron reduction potentials for these molecules.

Our computations to unravel the mechanism of photosynthetic ET have

confirmed that ubiquinone and its semiquinone anion can bind at different sites in the reaction center and attribute this difference to different protonation states of the key amino acids GluL212 and AspL213.
proposed a protein conformational gate controlling ubiquinone-B binding and migration, and possibly controlling electron transfer as well.
shown that activation energies for direct or gated ubiquinone migration from an electron transfer-inactive site distal to HisL190 to a putative ET-active site proximal to the His are within experimental error of a measured "electron transfer" activation energy.

Long-range goals include determining (1) how proteins modulate binding and electrochemistry of quinone electron acceptors; (2) how to tune ET thermodynamics and kinetics by varying quinone substituents or amino acid side chains; and (3) how to design more efficient energy storage devices modeled after the photosynthetic reaction center.

Selected publications:

Electron Transfer-Related Simulations:

Rahaman, Asif; Wheeler, R.A.; “Potential Energy Landscape for Conformationally Gated, Secondary Ubiquinone Binding in the Photosynthetic Reaction Center of Rhodobacter sphaeroides”; ChemPhysChem 2004, 5, 249-252.

Walden, Susan E.; Wheeler, R.A.; "A Protein Conformational Gate Controlling Binding Site Preference and Migration of Ubiquinone-B in the Photosynthetic Reaction Center of Rhodobacter sphaeroides"; J. Phys. Chem. B 2002, 106, 3001-3006.

Grafton, Anthony Kurt; Wheeler, R.A.; "Amino Acid Protonation States Determine Binding Sites of the Secondary Ubiquinone and its Anion in the Rhodobacter sphaeroides Photosynthetic Reaction Center; J. Phys. Chem. B 1999, 103, 5380-5387.

Quinone Thermochemistry:

Wise, Kristopher E.; Grafton, Anthony Kurt; Wheeler, R.A.; "Trimethyl-p-Benzoquinone Provides Excellent Structural, Spectroscopic, and Thermochemical Models for Plastoquinone-1 and its Radical Anion"; J. Phys. Chem. A 1997, 101, 1160-1165.

Raymond, Kevin S.; Grafton, Anthony Kurt; Wheeler, R.A.; "Calculated One-Electron Reduction Potentials and Solvation Structures for Selected p-Benzoquinones in Water"; J. Phys. Chem. B 1997, 101, 623-631.

Boesch, Scott E.; Grafton, Anthony Kurt; Wheeler, R.A.; "Electron Affinities for Substituted p-Benzoquinones From Hybrid Hartree-Fock/Density-Functional Calculations"; J. Phys. Chem. 1996, 100, 10083-10087.

Wheeler, R.A.; "A Method for Computing One-Electron Reduction Potentials and its Application to p-Benzoquinone in Water at 300 K"; J. Am. Chem. Soc. 1994, 116, 11048-11051.

Quinone Structures/Vibrations:

Wheeler, R.A.; "Quinones and Quinoidal Radicals in Photosynthesis" in Theoretical Biochemistry--Processes and Properties; L.A. Eriksson, ed.; Elsevier: Amsterdam, 2001; pp. 655-690.

Boesch, Scott E.; Wheeler, R.A.; "Structures and Properties of Ubiquinone-1 and its Radical Anion Predicted from a Hybrid Hartree-Fock/Density Functional Method"; J. Phys. Chem. A 1997, 101, 5799-5804.

Razeghifard, M. Reza; Kim, Sunyoung; Patzlaff, Jason; Hutchison, Ronald, S.; Krick, Thomas; Ayala, Idelisa; Steenhuis, Jacqueline J.; Boesch, Scott E.; Wheeler, R. A.; Barry, Bridgette, A.; "In vivo, In vitro, and Calculated Vibrational Spectra of Plastoquinone and Plastoquinone Anion Radical"; J. Phys. Chem. B 1999, 103, 9790-9800.

Grafton, Anthony Kurt; Wheeler, R.A.; "Comparison of the Properties of Various Fused-Ring Quinones and Their Radical Anions Using Hartree-Fock and Hybrid Hartree-Fock/Density Functional Methods"; J. Phys. Chem. A 1997, 101, 7154-7166.

Grafton, Anthony Kurt; Boesch, Scott E.; Wheeler, R.A.; "Structures and Properties of Vitamin K and its Radical Anion Predicted by Hybrid Hartree-Fock/Density Functional Theory"; J. Mol. Struc. (Theochem) 1997, 392, 1-11.