Biochemistry Department

Richard Debus

Dr. Richard Debus

Richard J. Debus
Professor of Biochemistry

Department of Biochemistry

Physical Biochemistry

Debus Research Group
PubMed Citations


Dr. Debus received his B.S. degree in chemistry from Caltech in 1977 and his M.S. and Ph.D. degrees in Chemistry from UC San Diego in 1980 and 1985, respectively.  His doctoral studies were conducted in the laboratories of Professors George Feher and Melvin Y. Okamura in the Department of Physics and involved spectroscopic characterizations of biochemically modified photosynthetic bacterial reaction centers.  He was a postdoctoral fellow in the plant molecular biology laboratory of Professor Lee McIntosh at the Department of Energy’s Plant Research Laboratory at Michigan State University from 1985-1988.  While at MSU, Dr. Debus interacted strongly with Professor Gerald T. Babcock, a well-known physical chemist and expert on Photosystem II (PSII).  As a result of his interactions with McIntosh and Babcock, Dr. Debus conducted the site-directed mutagenesis studies that identified the two redox-active tyrosine residues in PSII (now known as YZ and YD) as specific residues in two PSII subunits.  In 1988, he joined the Department of Biochemistry as an Assistant Professor.  At UC Riverside, Professor Debus’s has combined his postdoctoral training in molecular biology with his graduate training in biophysics/biochemistry with the aim of elucidating the mechanism of O2 production by the Mn4CaO5 catalyst in PSII.  He served as Chair of the Department of Biochemistry from 2010-2017. 

Research Interests

Our research program focuses on elucidating the molecular mechanism of photosynthetic O2 production.  This process is catalyzed by the Mn4CaO5 cluster in Photosystem II (PSII) and provides nearly our entire supply of atmospheric oxygen.  The Mn4CaO5 cluster accumulates oxidizing equivalents in response to light-driven photochemical events within PSII and then oxidizes two molecules of water to O2 in the final step of a five-step cycle.  Water oxidation is an extremely difficult chemical reaction, both thermodynamically and kinetically.  The Mn4CaO5 cluster catalyzes this reaction far more efficiently than any synthetic catalyst because its protein environment controls the cluster’s reactivity at each step in the catalytic cycle.  This control is accomplished by precise choreography of the proton and electron transfer reactions associated with water oxidation and by careful management of both substrate (water) access and proton egress.  Our primary goal is to identify the amino acid residues that are responsible for this control and to determine the role of each.  Currently, our specific goals are (1) to further delineate the dominant water access and proton egress pathways that link the Mn4CaO5 cluster with the thylakoid lumen and (2) to characterize the influence of specific residues on the water molecules that serve as substrate or as participants in the networks of hydrogen bonds that make up these pathways.  Proton egress through these pathways provides the thermodynamic driving force for oxidizing the Mn4CaO5 cluster in its higher oxidation states.  Our primary investigative tool is infrared (IR) spectroscopy.  We are employing FTIR difference spectroscopy to characterize mutant PSII core complexes containing single amino acid substitutions of residues identified crystallographically or computationally as potentially participating in these networks or otherwise interacting with the Mn4CaO5 cluster.  Identifying these residues will improve our understanding of the dynamic mechanism of water oxidation by the Mn4CaO5 cluster and will provide insight into the design of new generations of synthetic catalysts that convert sunlight into useful forms of storable energy.  

 Awards and Honors
  • Ph.D., University of California, San Diego, 1985
  • McKnight Foundation Postdoctoral Fellow in Photosynthesis, 1985-1986
  • NSF Postdoctoral Fellow in Plant Biology, 1986-1988
  • Fellow, American Association for the Advancement of Science, 2009

Selected Publications
  • Kim, C. J. and Debus, R. J. (2017) "Evidence from FTIR Difference Spectroscopy That a Substrate H2O Molecule for O2 Formation in Photosystem II Is Provided by the Ca Ion of the Catalytic Mn4CaO5 Cluster." Biochemistry 56, 2558-2570. http://pubs.acs.org/doi/abs/10.1021/acs.biochem.6b01278

  • Debus, R. J. (2016) "Identifying Carboxylate ligand Vibrational Modes in Photosystem II with QM/MM Methods," Proc. Nat'l. Acad. Sci. (USA) 113, 12613–12615 www.pnas.org/cgi/doi/10.1073/pnas.1615794113

  • Vinyard, D. J.. Askerka, M., Debus, R. J., Batista, V. S. and Brudvig, G. W. (2016) “Ammonia Binding in the Second Coordination Sphere of the Oxygen-​Evolving Complex of Photosystem II,” Biochemistry, 55, 4432-4436 (http://pubs.acs.org/doi/abs/10.1021/acs.biochem.6b00543).

  • Oyala, P. H., Stich, T. A., Debus, R. J., and Britt, R. D. (2015) “Ammonia Binds to the Dangler Manganese of the Photosystem II Oxygen-Evolving Complex,” Journal of the American Chemical Society, 137, 8829-8837.

  • Pokhrel, R., Debus, R. J., and Brudvig, G. W. (2015) “Probing the Effect of Mutations of Asparagine 181 in the D1 Subunit of Photosystem II, Biochemistry 54, 1663-1672.

  • Debus, R. J. (2015) “FTIR Studies of Metal Ligands, Networks of Hydrogen Bonds, and Water Molecules Near the Active Site Mn4CaO5 Cluster in Photosystem II,” Biochimica et Biophysica Acta 1847, 19-34.

  • Debus, R. J. (2014) “Evidence from FTIR Difference Spectroscopy That D1-Asp61 Influences the Water Reactions of the Oxygen-Evolving Mn4CaO5 Cluster of Photosystem II,” Biochemistry 53, 2941-2955.

  • Service, R. J., Hiller, W., and Debus, R. J. (2014) “A Network of Hydrogen Bonds near the Oxygen-Evolving Mn4CaO5 Cluster of Photosystem II Probed with FTIR Difference Spectroscopy,” Biochemistry 53, 1001-1017.

  • Service, R. J., Yano, J., Dilbeck, P. L., Burnap, R. L., Hiller, W., and Debus, R. J. (2013) “Participation of Glutamate-333 of the D1 Polypeptide in the Ligation of the Mn4CaO5 Cluster in Photosystem II,” Biochemistry 52, 8452-8464

  • Pokhrel, R., Service, R. J., Debus, R. J., and Brudvig, G. W. (2013) “Mutation of Lysine 317 in the D2 Subunit of Photosystem II Alters Chloride Binding and Proton Transport,” Biochemistry 52, 4758-4773.

  • Stich, T. A., Yeagle, G. J., Service, R. J., Debus, R. J., and Britt. R. D. (2011) “Ligation of D1-His332 and D1-Asp170 to the Manganese Cluster of Photosystem II from Synechocystis Assessed by Multifrequency Pulse EPR Spectroscopy,” Biochemistry 50, 7390-7404.

  • Yano, J., Walker, L. M., Strickler, M. A., Service, R. J., Yachandra, V. K., and Debus, R. J. (2011) “Altered Structure of the Mn4Ca Cluster in the Oxygen-evolving Complex of Photosystem II by a Histidine Ligand Mutant” Journal of Biological Chemistry 286, 9257-9267.

  • Service, R. J., Yano, J., McConnell, I., Hwang, H. J., Niks, D., Hille, R., Wydrzynski, T., Burnap, R. L., Hillier, W., and Debus, R. J. (2011) “Participation of Glutamate-354 of the CP43 Polypeptide in the Ligation of Mn and the Binding of Substrate Water in Photosystem II,” Biochemistry 50, 63-81.

  • Service, R. J., Hillier, W., and Debus, R. J. (2010) “Evidence from FTIR Difference Spectroscopy of an Extensive Network of Hydrogen Bonds near the Oxygen-Evolving Mn4Ca cluster of Photosystem II Involving D1-Glu65, D2-Glu312, and D1-Glu329,” Biochemistry 49, 6566-6669.
  • Stull, J. A., Stich, T. A., Service, R. J., Debus, R. J., Mandal, S. K., Armstrong, W. H., and Britt, R. D. (2010) “13C ENDOR Reveals That the D1 Polypeptide C-Terminus is Directly Bound to Mn in the Photosystem II Oxygen Evolving Complex,” J. Am. Chem. Soc. 132, 446-447.

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