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601 results on '"Kirk, Martin L."'

1. Spectroscopic Studies of Mononuclear Molybdenum Enzyme Centers

Author

Kirk, Martin L and Hille, Russ

Subjects
Inorganic Chemistry, Chemical Sciences, Electron Spin Resonance Spectroscopy, Molybdenum, xanthine oxidase, sulfite oxidase, DMSO reductase, electronic absorption spectroscopy, EPR spectroscopy, X-ray absorption spectroscopy, resonance Raman spectroscopy, magnetic circular dichroism spectroscopy, Medicinal and Biomolecular Chemistry, Organic Chemistry, Theoretical and Computational Chemistry, Medicinal and biomolecular chemistry, Organic chemistry
Abstract

A concise review is provided of the contributions that various spectroscopic methods have made to our understanding of the physical and electronic structures of mononuclear molybdenum enzymes. Contributions to our understanding of the structure and function of each of the major families of these enzymes is considered, providing a perspective on how spectroscopy has impacted the field.

Published
2022

7. The Role of the Pyranopterin Dithiolene Component of Moco in Molybdoenzyme Catalysis

Author

Nieter Burgmayer, Sharon J., Kirk, Martin L., Mingos, David Michael P., Series Editor, Cardin, Christine, Editorial Board Member, Duan, Xue, Editorial Board Member, Gade, Lutz H., Editorial Board Member, Gómez-Hortigüela Sainz, Luis, Editorial Board Member, Lu, Yi, Editorial Board Member, Macgregor, Stuart A., Editorial Board Member, Neese, Frank, Editorial Board Member, Pariente, Joaquin Perez, Editorial Board Member, Schneider, Sven, Editorial Board Member, Stalke, Dietmar, Editorial Board Member, and Ribbe, Markus W., editor

Published
2019
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10. Active Site Characterization of a Campylobacter jejuniNitrate Reductase Variant Provides Insight into the Enzyme Mechanism

Author

Yang, Jing, Mintmier, Breeanna, KC, Khadanand, Metzger, Mikayla C., Radhakrishnan, Manohar, McGarry, Jennifer, Wilcoxen, Jarett, Basu, Partha, and Kirk, Martin L.

Abstract

Mo K-edge X-ray absorption spectroscopy (XAS) is used to probe the structure of wild-type Campylobacter jejuninitrate reductase NapA and the C176A variant. The results of extended X-ray absorption fine structure (EXAFS) experiments on wtNapA support an oxidized Mo(VI) hexacoordinate active site coordinated by a single terminal oxo donor, four sulfur atoms from two separate pyranopterin dithiolene ligands, and an additional S atom from a conserved cysteine amino acid residue. We found no evidence of a terminal sulfido ligand in wtNapA. EXAFS analysis shows the C176A active site to be a 6-coordinate structure, and this is supported by EPR studies on C176A and small molecule analogs of Mo(V) enzyme forms. The SCysis replaced by a hydroxide or water ligand in C176A, and we find no evidence of a coordinated sulfhydryl (SH) ligand. Kinetic studies show that this variant has completely lost its catalytic activity toward nitrate. Taken together, the results support a critical role for the conserved C176 in catalysis and an oxygen atom transfer mechanism for the catalytic reduction of nitrate to nitrite that does not employ a terminal sulfido ligand in the catalytic cycle.

Published
2024
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15. 13C and 63,65Cu ENDOR studies of CO Dehydrogenase from Oligotropha carboxidovorans. Experimental Evidence in Support of a Copper–Carbonyl Intermediate

Author

Shanmugam, Muralidharan, Wilcoxen, Jarett, Habel-Rodriguez, Diana, Cutsail, George E, Kirk, Martin L, Hoffman, Brian M, and Hille, Russ

Subjects
Inorganic Chemistry, Chemical Sciences, Aldehyde Oxidoreductases, Alphaproteobacteria, Catalytic Domain, Copper, Electron Spin Resonance Spectroscopy, Models, Molecular, Multienzyme Complexes, General Chemistry, Chemical sciences, Engineering
Abstract

We report here an ENDOR study of an S = 1/2 intermediate state trapped during reduction of the binuclear Mo/Cu enzyme CO dehydrogenase by CO. ENDOR spectra of this state confirm that the (63,65)Cu nuclei exhibits strong and almost entirely isotropic coupling to the unpaired electron, show that this coupling atypically has a positive sign, aiso = +148 MHz, and indicate an apparently undetectably small quadrupolar coupling. When the intermediate is generated using (13)CO, coupling to the (13)C is observed, with aiso = +17.3 MHz. A comparison with the couplings seen in related, structurally assigned Mo(V) species from xanthine oxidase, in conjunction with complementary computational studies, leads us to conclude that the intermediate contains a partially reduced Mo(V)/Cu(I) center with CO bound at the copper. Our results provide strong experimental support for a reaction mechanism that proceeds from a comparable complex of CO with fully oxidized Mo(VI)/Cu(I) enzyme.

Published
2013

35. Long-range spin dependent delocalization promoted by the pseudo Jahn-Teller effect.

Author

Stein, Benjamin W., Dickie, Diane A., Nedungadi, Sachin, Brook, David J. R., Shultz, David A., and Kirk, Martin L.

Subjects
JAHN-Teller effect, MATHEMATICAL complexes, COBALT
Abstract

Strong spin-dependent delocalization (double exchange) was previously demonstrated for the complexes, NN-Bridge-SQ-Coiii(py)2Cat-Bridge-NN (where NN = S = 1 2 nitronylnitroxide, Bridge = 1,4-phenylene and single bond, SQ = S = 1 2 orthobenzosemiquinone, Coiii = low-spin d6 cobalt 3+, and Cat = diamagnetic catecholate). The mixed-valent S = 1 2 SQ-Coiii-Cat triad results in ferromagnetic alignment of localized (pinned) NN spins which are ∼22 Å apart (Bridge = Ph). Herein, we report similar ferromagnetic coupling of localized verdazyl (Vdz) radical spins. The origin of the magnetic exchange results from a second order vibronic effect (pseudo Jahn-Teller effect) in [Vdz-diox-Ru(py)2-diox-Vdz]0, which possesses a diamagnetic [diox-Ru-diox]0 triad by virtue of strong antiferromagnetic SQ-Ruiii exchange. [ABSTRACT FROM AUTHOR]

Published
2019
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44. Electronic structure description of the cisMoOS unit in models for molybdenum hydroxylases

Author

Doonan, Christian J., Rubie, Nick D., Peariso, Katrina, Harris, Hugh H., Knottenbelt, Sushilla Z., George, Graham N., Young, Charles G., and Kirk, Martin L.

Subjects
Molybdenum compounds -- Research, Molybdenum compounds -- Chemical properties, X-ray spectroscopy -- Usage, Chemistry
Abstract

The electronic structures of the cis-MoOS unit is studied by using S K-edge X-ray absorption spectroscopy (XAS) and vibrational spectroscopies coupled with bonding calculations. The electronic structure of the oxidized enzyme site has played a role in polarizing a substrate carbon center for nucleophilic attack by metal activated water and has acted as an electron sink in the two-electron oxidation of substrates.

Published
2008

45. Identification and characterisation of the Volvox carteri Moco carrier protein

Author

Hercher, Thomas W., Krausze, Joern, Yang, Jing, Kirk, Martin L., and Kruse, Tobias

Subjects
Models, Molecular, Protein Conformation, Coenzymes, Plant Biology, Article, Prosthetic Group Transfer, Structure-Activity Relationship, Molybdenum Cofactor, Chemical Biology, prosthetic group transfer, Metalloproteins, Molybdenum cofactor, Veröffentlichung der TU Braunschweig, Protein Interaction Domains and Motifs, Research Articles, ddc:5, Plant Proteins, prosthetic group insertion, Pteridines, Prosthetic Group Insertion, ddc:57, Volvox, Publikationsfonds der TU Braunschweig, Carrier Proteins, Molybdenum Cofactors, Protein Binding
Abstract

The molybdenum cofactor (Moco) is a redox active prosthetic group found in the active site of Moco-dependent enzymes (Mo-enzymes). As Moco and its intermediates are highly sensitive towards oxidative damage, these are believed to be permanently protein bound during synthesis and upon maturation. As a major component of the plant Moco transfer and storage system, proteins have been identified that are capable of Moco binding and release but do not possess Moco-dependent enzymatic activities. The first protein found to possess these properties was the Moco carrier protein (MCP) from the green alga Chlamydomonas reinhardtii. Here, we describe the identification and biochemical characterisation of the Volvox carteri (V. carteri) MCP and, for the first time, employ a comparative analysis to elucidate the principles behind MCP Moco binding. Doing so identified a sequence region of low homology amongst the existing MCPs, which we showed to be essential for Moco binding to V. carteri MCP.

Published
2020

46. Mo and W Cofactors and the Reactions they Catalyze

Author

KC, Khadanand and Kirk, Martin L.

Subjects
Molybdenum, Sulfite Oxidase, Biocatalysis, Article, Tungsten
Abstract

The last 20 years has seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by pyranopterin Mo and W enzymes. These enzyme possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role plays Moco in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess di-oxo active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is a component of an unusual and complex hydroxylation reaction that activates and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The contribution primarily highlights developments in the field that have occured since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical pyranopterin Mo enzymes XO, SO, and DMSO reductase.

Published
2020

47. Metal–Dithiolene Bonding Contributions to Pyranopterin Molybdenum Enzyme Reactivity

Author

Yang, Jing, Enemark, John H., and Kirk, Martin L.

Subjects
pyranopterin molybdenum enzymes, metal-dithiolene, molybdenum cofactor, chemistry.chemical_element, Context (language use), Electronic structure, tungsten enzymes, Tungsten, 010402 general chemistry, 01 natural sciences, Article, Inorganic Chemistry, chemistry.chemical_compound, moco, lcsh:Inorganic chemistry, Reactivity (chemistry), pseudo-jahn–teller effect, 010405 organic chemistry, Ligand, electronic structure, Small molecule, thione, lcsh:QD146-197, 0104 chemical sciences, Crystallography, chemistry, Molybdenum, pseudo-Jahn-Teller effect, Molybdenum cofactor, metal–dithiolene, fold-angle
Abstract

Here we highlight past work on metal−dithiolene interactions and how the unique electronic structure of the metal−dithiolene unit contributes to both the oxidative and reductive half reactions in pyranopterin molybdenum and tungsten enzymes. The metallodithiolene electronic structures detailed here were interrogated using multiple ground and excited state spectroscopic probes on the enzymes and their small molecule analogs. The spectroscopic results have been interpreted in the context of bonding and spectroscopic calculations, and the pseudo-Jahn−Teller effect. The dithiolene is a unique ligand with respect to its redox active nature, electronic synergy with the pyranopterin component of the molybdenum cofactor, and the ability to undergo chelate ring distortions that control covalency, reduction potential, and reactivity in pyranopterin molybdenum and tungsten enzymes.

Published
2020

49. Terminal gold-oxo complexes

Author

Rui Cao, Anderson, Travis M., Piccoli, Paula M.B., Schultz, Arthur J., Koetzle, Thomas F., Geletii, Yurii V., Slonkina, Elena, Hedman, Britt, Hodgson, Keith O., Hardcastle, Kenneth I., Xikui Fang, Kirk, Martin L., Knottenbelt, Sushilla, Kogerler, Paul, Musaev, Djamaladdin G., Morokuma, Keiji, Takahashi, Masashi, and Hill, Craig L.

Subjects
Oxo compounds -- Chemical properties, Oxo compounds -- Magnetic properties, Nuclear magnetic resonance spectroscopy -- Usage, Gold compounds -- Chemical properties, Gold compounds -- Magnetic properties, Chemistry
Abstract

Two terminal Au-oxo compounds are prepared and characterized by many physicochemical methods. These two compounds have established that both solids are diamagnetic and [super 31]P and [super 17]O NMR spectroscopy has confirmed that both have remained diamagnetic in solution.

Published
2007

50. Testing bridge-mediated differences in dinuclear valence tautomeric behavior

Author

Bin-Salamon, Sofi, Brewer, Scott H., Depperman, Ezra C., Franzen, Stefan, Kampf, Jeff W., Kirk, Martin L., Kumar, R. Krishna, Pearlso, Katrina, Preuss, Kathryn E., and Shultz, David A.

Subjects
Tautomers -- Structure, Tautomers -- Chemical properties, Pyridine -- Chemical properties, Chemistry
Abstract

The first two structurally, magnetically, and spectroscopically characterized dinuclear valence tautomerism (VT) complexes wherein the bridging ligand is the ancillary diimine and all three possible valence tautomeric forms and exist below 500K are reported. A combination of magnetic susceptibility, electronic absorption spectroscopy, and X-ray absorption spectroscopy (XAS) at the Co K-edge to probe the effects of environment on VT equilibria.

Published
2006

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