David J Singel

David J Singel
Montana State University | MSU · Department of Chemistry & Biochemistry

Ph.D.

About

120
Publications
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Publications

Publications (120)
Article
The allosteric transition within tetrameric hemoglobin (Hb) that allows both full binding to four oxygen molecules in the lung and full release of four oxygens in hypoxic tissues would earn Hb the moniker of ‘honorary enzyme’. However, the allosteric model for oxygen binding in hemoglobin overlooked the essential role of blood flow in tissue oxygen...
Article
Full-text available
Quantum biology is the study of quantum effects on biochemical mechanisms and biological function. We show that the biological production of reactive oxygen species (ROS) in live cells can be influenced by coherent electron spin dynamics, providing a new example of quantum biology in cellular regulation. ROS partitioning appears to be mediated duri...
Conference Paper
Full-text available
We propose some novel computational approaches to analyzing historical student transcript data to help improve course sequencing and generate default pathways for students to complete a college degree. Additionally, we examine whether there are “hidden prerequisites” to courses and whether there are courses which, when taken early in a student’s ca...
Article
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A three step protocol for protein S-nitrosothiol conversion to fluorescent mixed disulfides with purified proteins, referred to as the thiosulfonate switch, is explored which involves: (1) thiol blocking at pH 4.0 using S-phenylsulfonylcysteine (SPSC); (2) trapping of protein S-nitrosothiols as their S-phenylsulfonylcysteines employing sodium benze...
Article
Full-text available
The effects of weak magnetic fields on the biological production of reactive oxygen species (ROS) from intracellular superoxide (O2•-) and extracellular hydrogen peroxide (H2O2) were investigated in vitro with rat pulmonary arterial smooth muscle cells (rPASMC). A decrease in O2•- and an increase in H2O2 concentrations were observed in the presence...
Article
Full-text available
Electron magnetic resonance (EMR) spectroscopy was used to determine the magnetic properties of maghemite (γ-Fe(2)O(3)) nanoparticles formed within size-constraining Listeria innocua (LDps)-(DNA-binding protein from starved cells) protein cages that have an inner diameter of 5 nm. Variable-temperature X-band EMR spectra exhibited broad asymmetric r...
Article
Dendrimers are attractive templates to display functional molecular components. Since the behavior of dendrimer systems can depend greatly on the accessibility of these molecular components to the external environment, and on the spatial arrangement of functional groups attached to the dendrimer terminal branches (end-groups), techniques to determi...
Article
Full-text available
This work describes an approach for calculating and measuring dipolar interactions in multispin systems to monitor conformational changes in icosahedral protein cages using site-directed spin labeling. Cowpea chlorotic mottle virus (CCMV) is used as a template that undergoes a pH-dependent reversible capsid expansion wherein the protein cage swells...
Article
The chemical interplay of nitrogen oxides (NO's) with hemoglobin (Hb) has attracted considerable recent attention because of its potential significance in the mechanism of NO-related vasoactivity regulated by Hb. An important theme of this interplay-redox coupling in adducts of heme iron and NO's-has sparked renewed interest in fundamental studies...
Article
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The field of NO biology began two decades ago with the identification of nitric oxide, NO, as the endothelium-derived vascular relaxing factor (EDRF) discovered by Furchgott [1]. Since then, the scope of the field has dramatically expanded to view the NO moiety as a ubiquitous signaling agent [2] that can modulate effector function through a variet...
Article
Angle-dependent electron magnetic resonance was performed on 4.9, 8.0, and 19 nm iron oxide nanoparticles encapsulated within protein capsids and suspended in water. Measurements were taken at liquid nitrogen temperature after cooling in a 1 T field to partially align the particles. The angle dependence of the shifts in the resonance field for the...
Article
Hemoglobins are found in organisms from every major phylum and subserve life-sustaining respiratory functions across a broad continuum. Sustainable aerobic respiration in mammals and birds relies on the regulated delivery of oxygen (O2) and nitric oxide (NO) bioactivity by hemoglobin, through reversible binding of NO and O2 to hemes as well as S-ni...
Article
EPR spectroscopy was used to evaluate the dynamic motions of dendrimer end groups for a G(4)-PAMAM dendrimer. Clusters of end groups were covalently tethered together and then selectively labeled with PROXYL groups upon removal of the tether. Analysis of the EPR spectra of the spin-labeled dendrimers suggests that initial end group proximity does n...
Article
Full-text available
Nitric oxide (NO) bioactivity is mainly conveyed through reactions with iron and thiols, furnishing iron nitrosyls and S-nitrosothiols with wide-ranging stabilities and reactivities. Triiodide chemiluminescence methodology has been popularized as uniquely capable of quantifying these species together with NO byproducts, such as nitrite and nitrosam...
Article
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There has been much discussion within the literature concerning the measurement of NO-related species that are formed in reaction with hemoglobin (Hb). These studies are of great interest in terms of understanding the role of Hb in relation to vascular control. However, these studies are inherently
Article
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Genetic and biochemical data demonstrate a pivotal role for S-nitrosothiols (SNOs) in mediating the actions of nitric oxide synthases (NOSs). SNOs serve to convey NO bioactivity and to regulate protein function. This understanding is of immediate interest to the pulmonary clinical and research communities. This article reviews the following: (1) bi...
Article
Full-text available
Red blood cells (RBCs) act as O2-responsive transducers of vasodilator and vasoconstrictor activity in lungs and tissues by regulating the availability of nitric oxide (NO). Vasodilation by RBCs is impaired in diseases characterized by hypoxemia. We have proposed that the extent to which RBCs constrict vs. dilate vessels is, at least partly, contro...
Article
Starburst dendrimers are receiving considerable attention as templates for the assembly of structured arrays of molecular components. This research motivates the development of improved methods for dendrimer characterization-specifically, for determining the numbers, distributions of numbers, and spatial distribution of molecular species synthetica...
Article
Full-text available
The mechanism by which hypoxia [low partial pressure of O2 (pO2)] elicits signaling to regulate pulmonary arterial pressure is incompletely understood. We considered the possibility that, in addition to its effects on smooth muscle, hypoxia may influence pulmonary vascular tone through an effect on RBCs. We report that exposure of native RBCs to su...
Article
Full-text available
Magnetic and structural properties determined by electron magnetic resonance (EMR) spectroscopy are reported for maghemite (γ- Fe <sub>2</sub> O <sub>3</sub>) nanoparticles formed through template-constrained mineralization within three protein cages with nominal diameters of 5, 8, and 24 nm. EMR spectra, obtained at 4.0, 9.2, 34.6, 94.9, and 130.0...
Article
Full-text available
Hypoxic vasodilation involves detection of the oxygen content of blood by a sensor, which rapidly transduces this signal into vasodilatory bioactivity. Current perspectives on the molecular mechanism of this function hold that hemoglobin (Hb) operates as both oxygen sensor and a condition-responsive NO reactor that regulates the dispensing of bioac...
Article
Blood flow in the microcirculation is regulated by physiological oxygen (O2) gradients that are coupled to vasoconstriction or vasodilation, the domain of nitric oxide (NO) bioactivity. The mechanism by which the O2 content of blood elicits NO signaling to regulate blood flow, however, is a major unanswered question in vascular biology. While the h...
Article
Mannose-TEMPO functionalized G4-PAMAM dendrimers with increasing mannose loadings have been synthesized and characterized by MALDI-TOF MS and EPR spectroscopy. Analysis of linebroadening effects in the EPR spectra of these dendrimers allowed us to determine the relative presentation of mannose and TEMPO on the dendrimer surface. Hemagglutination as...
Article
Recent studies have suggested that binding of oxygen to hemoglobin (Hb) facilitates reactions of nitric oxide (NO) that lead to production of S-nitrosohemoglobin (SNO-Hb), and that vasodilator S-nitrosthiol (SNO) is dispensed by red blood cells (RBCs) at low oxygen tension (pO2) to dilate blood vessels. In human lungs, NO bioactivity serves to atte...
Article
Physiological O2 gradients are principal regulators of blood flow in the microcirculation: position-to-position changes in hemoglobin (Hb) O2 saturation are coupled to regulated vasodilation (“hypoxic vasodilation”). The mechanism by which graded changes in O2 content of blood evoke this response has been a great challenge to understand. A new role...
Article
Red blood cell vasodilation: nitric oxide and haemoglobin help to match blood flow to metabolic demand.
Article
Protein-carbohydrate interactions play a critical role in many biological recognition events. Multivalent therapeutic agents that utilize protein-carbohydrate interactions have proven difficult to design, primarily because the fundamental requirements of protein-carbohydrate interactions are not well understood. Here, we report a systematic study o...
Article
Full-text available
Crawford and colleagues[1][1] have studied the effects of heme oxidation, glutathione (GSH), and oxygenation (pO2) on the bioactivity of S-nitrosohemoglobin (SNOHb). They report that (1) SNOHb in the ferric or met oxidation state (SNOmetHb) is a more potent vasodilator than SNOHb in the oxygenated
Article
Full-text available
Previous studies of the interactions of NO with human hemoglobin have implied the predominance of reaction channels that alternatively eliminate NO by converting it to nitrate, or tightly complex it on the alpha subunit ferrous hemes. Both channels could effectively quench NO bioactivity. More recent work has raised the idea that NO groups can effi...
Article
Previous studies of the interactions of NO with human hemoglobin have implied the predominance of reaction channels that alternatively eliminate NO by converting it to nitrate, or tightly complex it on the alpha subunit ferrous hemes. Both channels could effectively quench NO bioactivity. More recent work has raised the idea that NO groups can effi...
Article
Full-text available
Interactions of nitric oxide (NO) with hemoglobin (Hb) could regulate the uptake and delivery of oxygen (O(2)) by subserving the classical physiological responses of hypoxic vasodilation and hyperoxic vasconstriction in the human respiratory cycle. Here we show that in in vitro and ex vivo systems as well as healthy adults alternately exposed to hy...
Article
Full-text available
The Final Technical Report for Grant F49620-96-1-0443 "Electron Transfer Chemistry in Optical Materials: an EPR Investigation of Radiation-Induced Defects in Chemically Modified Materials" details the construction, and performance-evaluation of a 94.9 GHz EPR (electron paramagnetic resonance) spectrometer, operating in both CW (continuous wave) and...
Article
The means by which the protein GAP accelerates GTP hydrolysis, and thereby downregulates growth signaling by p21Ras, is of considerable interest, particularly inasmuch as p21 mutants are implicated in a number of human cancers. A GAP "arginine finger," identified by X-ray crystallography, has been suggested as playing the principal role in the GTP...
Article
Electron-magnetic resonance spectroscopy and computational studies of the cysteine cross-linked tyrosyl radical in apogalactose oxidase have led to conflicting ideas regarding spectral assignments and protein-environment effects. We report DFT calculations on model radicals that clarify these issues. Calculated Fermi contact interactions do not res...
Article
Full-text available
S-Nitrosohemoglobin (SNO-Hb) is a vasodilator whose activity is allosterically modulated by oxygen ("thermodyamic linkage"). Blood vessel contractions are favored in the oxygenated structure, and vasorelaxant activity is "linked" to deoxygenation, as illustrated herein. We further show that transnitrosation reactions between SNO-Hb and ambient thio...
Article
Full-text available
The oxidation of nitric oxide (NO) to nitrate by oxyhemoglobin is a fundamental reaction that shapes our understanding of NO biology. This reaction is considered to be the major pathway for NO elimination from the body; it is the basis for a prevalent NO assay; it is a critical feature in the modeling of NO diffusion in the circulatory system; and...
Article
High-frequency electron paramagnetic resonance (EPR) spectroscopy has been performed on a nitroxide spin-labeled peptide in fluid aqueous solution. The peptide, which follows the single letter sequence, was reacted with the methanethiosulfonate spin label at the cysteine sulfur. The spin sensitivity of high-frequency EPR is excellent with less than...
Article
Initial results are reported of an EPR study, conducted at 94.9 GHz, of a thermally annealed, neutron-irradiated white sapphire (α-Al2O3) single-crystal fiber. The optical centers produced in sapphire by neutron irradiation and thermal annealing are of interest for optical technologies involving the phenomenon of spectral hole-burning. While these...
Article
Electron spin-echo envelope modulation (ESEEM) spectroscopy is widely used to investigate the active sites of biological molecules in frozen solutions. Various cryoprotection techniques, particularly the addition of co-solvents, are commonly employed in the preparation of such samples. In conjunction with ESEEM studies of Mn(II) guanosine nucleotid...
Article
The G protein p21 ras is a molecular switch in the signal transduction pathway for cellular growth and differentiation. Hydrolysis of tightly bound GTP alters the conformation of p21, terminating the signal. The coordination of the p21 residue Thr35 to Mg2+ in its active site, which has been observed in the crystal structure of p21 in complex with...
Article
The activated form of galactose oxidase from the fungus Dactylium dendroides contains a single divalent copper ion which is antiferromagnetically coupled to a protein-based free radical. Chemical oxidation of the apoenzyme generates the free radical which is localized on a covalently cross-linked tyrosine - cysteine residue. This species, together...
Article
As a molecular switch, the ras protein p21 undergoes structural changes that couple recognition sites on the protein surface to the guanine nucleotide-divalent metal ion binding site. X-ray crystallographic studies of p21 suggest that coordination between threonine-35 and the divalent metal ion plays an important role in these conformational change...
Article
Electron paramagnetic resonance spectroscopy at 139.5 GHz has been used to study p21 ras complexed with Mn(II) and guanosine 5'-(beta, gamma-imidotriphosphate), an analog of GTP. The p21 sample studied was selectively labeled with [17O gamma]threonine to a final enrichment of 30%. A Mn(II)-17O hyperfine interaction was observed, but the value of th...
Article
Full-text available
Chemical modification of proteins is a common theme in their regulation. Nitrosylation of protein sulfhydryl groups has been shown to confer nitric oxide (NO)-like biological activities and to regulate protein functions. Several other nucleophilic side chains -- including those with hydroxyls, amines, and aromatic carbons -- are also potentially su...
Article
A high-frequency dynamic nuclear polarization (DNP)/electron paramagnetic resonance spectrometer operating at 211 MHz for1H and 140 GHz forg= 2 paramagnetic centers (5 T static field) is described. The salient feature of the instrument is a cyclotron-resonance maser (gyrotron) which generates high-frequency, high-power microwave radiation. This gyr...
Article
Multifrequency ESEEM (electron spin echo envelope modulation) and EPR spectroscopies are employed to elucidate the electronic structure of the monoradical anion of tris(1,3-diphenyltriazenido)aluminum, [Al(dpt)3]-, which is obtained by the chemical reduction of Al(dpt)3. Analysis of the EPR and ESEEM spectra obtained for various isotope-labeling co...
Article
Electrochemical studies of Al(dpt)3 (Hdpt = 1,3-diphenyltriazene) by cyclic voltammetry in THF solution reveal three successive pseudo reversible one-electron reduction waves (E1/2 = -1.50, -1.84, and -2.16 V). The chemical reduction of Al(dpt)3 by sodium metal in THF allows for the isolation of the radical anion complexes [Na(THF)x]n[Al(dPt)3], n...
Article
Dynamic nuclear polarization (DNP) transfers the large polarization of unpaired electrons to nuclei and thus significantly enhances the signal strength in nuclear magnetic resonance (NMR) spectroscopy. High frequency/field (140 GHz/5 T) DNP has been implemented in solid state NMR experiments using a nitroxide radical as the paramagnetic polarizing...
Article
Electron-spin-echo spectroscopy on the lowest 3A2 state of Mn5+ ions in Ba3(VO4)2 in combination with pulsed laser excitation at 1176.6 nm proves that the laser activity in this material derives from the 1E⇆3A2 transition of the Mn5+ ion. This result is corroborated by Zeeman experiments on the 1E→3A2 emission line, which further reveal the Zeeman...
Article
1) The reactions of nitric oxide with superoxide can lend to neurotoxicity through formation of peroxynitrite, and not by NO. alone, at least under our conditions. 2) The reactions of NO+ equivalents with thiol groups on the NMDA receptor can lead to neuroprotection by inhibiting calcium influx. These findings suggest that cell function can be cont...
Article
Full-text available
A comprehensive report is presented on EPR and correlated optical spectroscopic studies conducted in our laboratory on a new class of solid-state materials with potential utility as near IR lasers. All of the studied materials involve oxide host lattices (Silicates, vanadates, and germanates) doped with 3d transition metal-ions (chromium and mangan...
Article
Selectively labeled samples of human H- or N-ras p21 ligated to MnIIGDP or MnIIGMPPNP were studied by electron spin-echo envelope modulation spectroscopy in order to define the protein environment around the divalent metal. We incorporated [4-13C]-labeled Asx into p21.MnIIGDP and found that the distance from the carboxyl 13C of Asp57 to MnII is app...
Article
A comprehensive experimental study of the magnetic field dependences of ESEEM (electron spin echo envelope modulation) for a spin one‐half nucleus in an orientationally disordered solid is presented. Modulation effects from the remote (unligated) nitrogen of 15N‐labeled imidazole in a Cu(II)–diethylenetriamine–15N‐imidazole complex were registered...
Article
Optical Zeeman spectra of the near-IR luminescent center in Cr:forsterite were obtained with an external magnetic field applied along the crystallographic a and c axes. The field-dependent sublevel splittings of the triplet spin ground state were resolved through fluorescence line narrowing (FLN) techniques. The excellent correspondence between the...
Article
1. The reactions of nitric oxide with superoxide can lead to neurotoxicity through formation of peroxynitrite, and not by NO. alone, at least under our conditions. 2. Transfer of NO+ groups to thiol(s) on the NMDA receptor can lead to neuroprotection by inhibiting Ca2+ influx. These findings suggest that cell function can be controlled by, or throu...
Article
Excessive production of nitric oxide, characteristic of inflamed states, may have deleterious effects through its facile conversion (in the presence of O2) to peroxynitrite, which promotes lipid and sulfhydryl oxidation. This study assessed the effect of peroxynitrite on the rat colon. Peroxynitrite was administered intrarectally to rats. One, 3, 7...
Article
Full-text available
Recent discoveries suggesting essential bioactivities of nitric oxide (NO.) in the lung are difficult to reconcile with the established pulmonary cytotoxicity of this common air pollutant. These conflicting observations suggest that metabolic intermediaries may exist in the lung to modulate the bioactivity and toxicity of NO.. We report that S-nitr...
Article
DNP (dynamic nuclear polarization) experiments at 5 T are reported, in which a cycoltron resonance maser (gyrotron) is utilized as a 20 W, 140 GHz microwave source to perform the polarization. MAS (magic angle spinning) NMR spectroscopy with DNP has been performed on samples of polystyrene doped with the free radical BDPA (alpha,gamma-bisdiphenylen...
Article
CONGENERS of nitrogen monoxide (NO) are neuroprotective and neurodestructive1– 7. To address this apparent paradox, we considered the effects on neurons of compounds characterized by alternative redox states of NO: nitric oxide (NO.) and nitrosonium ion (NO+)8. Nitric oxide, generated from NO. donors or synthesized endogenously after NMDA (N-methyl...
Article
S-nitrosothiols may serve as carriers in the mechanism of action of endothelium-derived relaxing factor (EDRF) by stabilizing the labile nitric oxide (NO) radical from inactivation by reactive species in the physiological milieu and by delivering NO to the heme activator site of guanylyl cyclase. Low-molecular-weight thiols, such as cysteine and gl...