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Nature uses enzymes containing transition elements to carry out a wide variety of hydrolytic and reduction-oxidation reactions with amazing selectivity. The Emerson laboratory is focused on uncovering the chemistry that is and can be catalyzed by transition metal centers in biology. To do this, we employ a combination of techniques from biochemistry, synthetic chemistry, and spectroscopy. Below are two examples of projects currently under investigation:
Carbonic Anhydrase (CA) is a ubiquitous enzyme that activates a water molecule to hydrolytically convert carbon dioxide (CO2) to the bicarbonate ion (HCO3-). CA utilizes a mononuclear zinc site and an extensive H-bonding network to activate water molecules (as shown above). Our aim is to develop catalysts or biocatalysts that use the hydrolytic chemistry similar to that found in CAs as a means to sequester CO2. Currently we are working in two areas: i) we are building small molecule, coordination complexes that mimic the coordination geometry, the H-bonding network, and the reactivity observed in CAs. ii) we are isolating and characterizing a CA from the endothermic organism Alligator mississippiensis.
N-oxygenases are enzymes that oxidize aromatic amines to nitro substituents. Two putative N-oxygenases have been identified in Streptomyces violaceoruber. These N-oxygenases, namely PrnD and AurF, serve in biosynthetic pathways, which eventually produce the antibiotic molecules pyrrolnitrin and aureothin, respectively. Although these enzymes catalyze similar reactions, they have quite different active site structures.
PrnD has sequence homology with Rieske (di)oxygenases (mononuclear iron active site with an adjacent Fe2S2 cluster), while AurF homologues have been identified as a bimetallic oxygenase. Together these enzymes highlight the diversity of nature's catalysts and provide a unique opportunity to study the parallel catalytic mechanisms of amine oxidation by these two different enzymes.
W. A. Gunderson, A. I. Zatsman, J. P. Emerson, E. R. Farquhar, L. Que Jr., J. D. Lipscomb, M. P. Hendrich, "Detection of Intermediates in the Enzymatic Cycle of an Extradiol Dioxygenase," J. Am. Chem. Soc. 2008 130, 14465-67
L. E. Grove, J. K. Hallman, J. P. Emerson, J. A. Halfen, T. C. Brunold Synthesis, X-Ray Crystallographic Characterization, and Electronic Structure Studies of a Di-Azide Iron(III) Complex: Implications for the Azide Adducts of Iron(III) Superoxide Dismutase," Inorg. Chem. 2008 47, 5762-74
J. P. Emerson, E. G. Kovaleva, E. R. Farquhar, J. D. Lipscomb, and L. Que, Jr., "Swapping Metals in Fe- and Mn-Dependent Dioxygenases. Evidence for Oxygen Activation Without a Change in Metal Redox State," Proc. Nat. Acad. Sci. USA 2008 105, 7347-52
V. W. Huang, J. P. Emerson, D. M. Kurtz, Jr., "The Reaction of Desulfovibrio vulgaris Two-Iron Superoxide Reductase with Superoxide: Insights from Stopped-flow Spectrophotometry," Biochemistry 2007 46, 11342-51
J. P. Emerson, E. R. Farquhar, and L. Que, Jr., "Structural "Snap-Shots" along Reaction Pathway of Non-heme Iron Enzymes," Angew. Chem. Int. Ed. 2007 46, 8553-6