Campus Directory

Division Physical & Biological Sciences Division

Department/College/Unit Chemistry & Biochemistry Department

Title Professor Emeritus

Affiliation Faculty

Faculty Type Emeriti

Areas of Expertise Biophysics
Chemistry

Primary Office Location Physical Sciences Building
NA

Mail Stop Chemistry

Biography, Education and Training

B.S., University of Iceland, Reykjavík
Ph.D., Colorado State University, Fort Collins

Summary of Expertise

Time-resolved spectroscopy, biophysics and bioenergetics, ligand binding and electron transfer dynamics of redox metalloproteins, heme-copper oxidases, proton translocation

Research Interests

The primary thrust of our research is to understand how protein environments tune ligand pathways and metal-based prosthetic groups in the respiratory heme-copper oxidases (HCOs) and nitric oxide reductases (NORs) to support specific catalytic functions under varying physiological conditions. To accomplish this goal, we have focused on establishing the functional roles of specific residues, constriction points, and docking sites in the various HCOs and, more recently, NORs, using both experimental and theoretical approaches. The HCOs catalyze a key step in energy production by aerobic organisms, which is the reduction of O2 to water that is coupled to proton translocation. The resulting electrochemical proton gradient is the energy source required for chemiosmotic ATP synthesis. The NORs, which are divergent members of the superfamily of the HCOs, catalyze the reduction of nitric oxide (NO) to nitrous oxide (N2O), an intermediate step in the denitrification process. NO is an important signaling molecule in many eukaryotes while N2O is a potent greenhouse gas. We have studied the reaction of O2 with HCOs on nanosecond and longer time scales using time-resolved multi-channel optical absorption spectroscopy. In conjunction with singular value decomposition and global exponential fitting analysis, this has allowed us to deduce the kinetics and the UV-Vis spectra of the transient intermediates generated during O2 reduction. We have also employed alternative strategies and tools to study HCOs and NORs function, including the use of photolabile O2 and NO carriers to investigate the reactions of these enzymes with O2 and NO, respectively. Our approach challenges traditional CO flash-photolysis techniques in which the reaction is initiated by photodissociation of the CO-bound reduced enzymes in the presence of O2 or NO. Instead, we are shifting the focus toward exploring the reactions of O2 and NO with the HCOs and NORs under more physiological conditions, namely, in the absence of CO.

Our combined experimental and theoretical approach has already provided atomic-level detail of the ligand channel in HCOs and the role it may play in tuning the enzymatic function for different physiological environments, such as the thermophilicity of the Thermus thermophilus bacterium. The photolabile carriers, in conjunction with a double-laser technique, also promise to provide a unique insight into the mechanism of NO reduction in the NORs.

Selected Publications

C. Funatogawa, Y, Li, Y. Chen, I. Szundi, W. McDonald, J. A. Fee, C. D. Stout, and Ó. Einarsdóttir, “Role of the Conserved Valine 236 in Access of Ligands to the Active Site of Thermus thermophilus ba3 Cytochrome Oxidase,” Biochemistry, 56, 107-119, 2017.

J, A. Cassano, S, Choi, W, McDonald, I. Szundi, T. R. Villa Gawboy,  R, B. Gennis, and Ó. Einarsdóttir, , “The CO Photodissociation and Recombination Dynamics of the W172Y/F282T Ligand Channel Mutant of Rhodobacter sphaeroides aa3 Cytochrome c Oxidase,” Photochemistry and Photobiology, 92, 410-419, 2016.

Ó. Einarsdóttir, W. McDonald, C. Funatogawa, I. Szundi, W. H. Woodruff and R. B. Dyer, “The pathway of O2 to the Active Site in Heme-Copper Oxidases,” Biochim. Biophys. Acta, 1847, 109-118, 2015.

I. Szundi, C. Kittredge, S. L. Choi, W. McDonald, J. Ray, R. B. Gennis, and Ó. Einarsdóttir, “Kinetics and Intermediates of the Reaction of Fully Reduced Escherichia coli bo3 Ubiquinol Oxidase with O2,” Biochemistry, 53, 5393-5404, 2014.

W. McDonald, C. Funatogawa, Y. Li, Y. Chen, I. Szundi, J.A. Fee, C.D. Stout and Ó. Einarsdóttir, “Conserved Glycine 232 in the Ligand Channel of ba3 Cytochrome Oxidase from Thermus thermophilus,” Biochemistry, 53, 4467-4475, 2014.

W. McDonald, C. Funatogawa, Y. Li, I. Szundi, Y. Chen, J. A. Fee, C. D. Stout, and Ó. Einarsdóttir, “Ligand Access to the Active Site in Thermus thermophilus ba3 and Bovine Heart aa3 Cytochrome Oxidases,” Biochemistry, 52, 640-652, 2012.

I. Szundi, C. Funatogawa, J. Cassano, W. McDonald, J. Ray, C. Hiser, S. Ferguson-Miller, R. B. Gennis, and Ó. Einarsdóttir, “Spectral Identification of Intermediates Generated during the Reaction of Dioxygen with the Wild-type and EQ(I-286) mutant of Rhodobacter sphaeroides Cytochrome c Oxidase,” Biochemistry 51, 9302-9311, 2012.

Ó. Einarsdóttir, C. Funatogawa, T. Soulimane, J. A. Fee, and I. Szundi, “Kinetic Studies of the Reactions of O2 and NO with Reduced Thermus thermophilus ba3 and Bovine aa3 using Photolabile Carriers,” Biochim. Biohys. Acta, 1817, 672-679, 2012.

            I. Szundi, C. Funatogawa, J.A. Fee, T. Soulimane, and Ó. Einarsdóttir, “CO Impedes Superfast O2 Binding in ba3 Cytochrome Oxidase from Thermus thermophilus,” Proc. Natl. Acad. Sci. USA 107, 21010-21015, 2010.