Extracting accurate distances and bounds from 2D NOE exchangeable proton peaks

1993 ◽  
Vol 115 (4) ◽  
pp. 1590-1591 ◽  
Author(s):  
He Liu ◽  
Anil Kumar ◽  
Klaus Weisz ◽  
Uli Schmitz ◽  
Karl D. Bishop ◽  
...  
Keyword(s):  
Exchangeable Proton

scholarly journals Electron-paramagnetic-resonance parameters of molybdenum(V) in sulphite oxidase from chicken liver

1980 ◽  
Vol 185 (2) ◽  
pp. 397-403 ◽  
Author(s):  
M T Lamy ◽  
S Gutteridge ◽  
R C Bary
Keyword(s):  
Hyperfine Coupling ◽  
Chemical Species ◽  
Hyperfine Coupling Constant ◽  
Chicken Liver ◽  
Paramagnetic Resonance ◽  
Phosphate Complex ◽  
Exchangeable Proton ◽  
Weakly Coupled ◽  
Sulphite Oxidase ◽  
Single Chemical

A study has been made of e.p.r. signals due to Mo(V) in reduced sulphite oxidase (EC 1.8.3.1) from chicken liver. Reduction by SO3(2-), or photochemically in the presence of a deazaflavin derivative, produces spectra indistinguishable from one another. Three types of spectra from the enzyme were distingusihed and shown to correspond to single chemical species, since they could be simulated at both 9 and 35 GHz by using the same parameters. These were the low-pH form of the enzyme, with gav. 1.9805, the high-pH form, with gav. 1.9681 and a phosphate complex, with gav. 1.9741. The low-H form shows interaction with a single exchangeable proton, with A(1H)av. (hyperfine coupling constant) = 0.98 mT, probably in the form of an MoOH group. Parameters of the signals are compared with those for signals from xanthine oxidase and nitrate reductase. The signal from the phosphate complex of sulphite oxidase in unique among anion complexes of Mo-containing enzymes in showing no hyperfine coupling to protons. There is no evidence for additional weakly coupled protons or nitrogen nuclei in the sulphite oxidase signals. The possibility is considered that the enzymic mechanism involves abstraction of a proton and two electrons from HSO3- by a Mo = O group in the enzyme.

Axial histidyl imidazole non-exchangeable proton resonances as indicators of imidazole hydrogen bonding in ferric cyanide complexes of heme peroxidases

1982 ◽  
Vol 708 (3) ◽  
pp. 317-325 ◽  
Author(s):  
Gerd N. La Mar ◽  
Jeffrey S. De Ropp ◽  
V.P. Chacko ◽  
James D. Satterlee ◽  
James E. Erman
Keyword(s):  
Hydrogen Bonding ◽  
Exchangeable Proton ◽  
Cyanide Complexes ◽  
Proton Resonances ◽  
Heme Peroxidases

Salicylic Acid and Analogues as diaCEST MRI Contrast Agents with Highly Shifted Exchangeable Proton Frequencies

2013 ◽  
Vol 125 (31) ◽  
pp. 8274-8277 ◽  
Author(s):  
Xing Yang ◽  
Xiaolei Song ◽  
Yuguo Li ◽  
Guanshu Liu ◽  
Sangeeta Ray Banerjee ◽  
...  
Keyword(s):  
Salicylic Acid ◽  
Contrast Agents ◽  
Mri Contrast Agents ◽  
Mri Contrast ◽  
Exchangeable Proton

scholarly journals Electron-paramagnetic-resonance studies on nitrate reductase from Escherichia coli K12

1978 ◽  
Vol 171 (3) ◽  
pp. 639-647 ◽  
Author(s):  
Stephen P. Vincent ◽  
Robert C. Bray
Keyword(s):  
Escherichia Coli ◽  
Nitrate Reductase ◽  
Extraction Procedure ◽  
Hydrophobic Interaction Chromatography ◽  
Low Ph ◽  
Paramagnetic Resonance ◽  
Escherichia Coli K12 ◽  
Exchangeable Proton ◽  
Ph Range ◽  
Nitrate And Nitrite

Nitrate reductase was purified from anaerobically grown Escherichia coli K12 by a method based on the Triton X-100 extraction procedure of Clegg[(1976) Biochem. J.153, 533–541], but hydrophobic interaction chromatography was used in the final stage. E.p.r. spectra obtained from the enzyme under a variety of conditions are well resolved and were interpreted with the help of the computer-simulation procedures of Lowe [(1978) Biochem. J.171, 649–651]. Parameters for five molybdenum(V) species from the enzyme are given. The low-pH species (gav. 1.9827) is in pH-dependent equilibrium with the high-pH species (gav. 1.9762), the pK for interconversion of the species being 8.26. Of a variety of anions tested, only nitrate and nitrite formed complexes with the enzyme (in the low-pH form), giving modified molybdenum(V) e.p.r. spectra. These complexes, as well as the low-pH form of the free enzyme, showed interaction of molybdenum with a single exchangeable proton. The fifth molybdenum(V) species, sometimes detected in small amounts, appears not to be due to functional nitrate reductase. After full reduction of the enzyme with dithionite, addition of nitrate caused reoxidation of molybdenum to the quinquivalent state, in a time less than the enzyme turnover. Activity of the enzyme in the pH range 6–10 is controlled by a pK of 8.2. It is suggested that the low-pH signal-giving species is the form of the enzyme involved in the catalytic cycle. Iron–sulphur and other e.p.r. signals from the enzyme are briefly described and the enzymic reaction mechanism is discussed.

scholarly journals pH-jump studies at subzero temperatures on an intermediate in the reaction of xanthine oxidase with xanthine

1978 ◽  
Vol 175 (3) ◽  
pp. 879-885 ◽  
Author(s):  
A D Tsopanakis ◽  
S J Tanner ◽  
R C Bray
Keyword(s):  
Nitrate Reductase ◽  
Xanthine Oxidase ◽  
Low Ph ◽  
High Ph ◽  
Ph Values ◽  
Exchangeable Proton ◽  
Subzero Temperatures ◽  
Ph Jump ◽  
Unique Nature ◽  
Prototropic Equilibrium

Xanthine oxidase is stable and active in aqueous dimethyl sulphoxide solutions of up to at least 57% (w/w). Simple techniques are described for mixing the enzyme in this solvent at–82 degrees C, with its substrate, xanthine. When working at high pH values under such conditions, no reaction occurred, as judged by the absence of e.p.r. signals. On warming to–60 degrees C, for 10 min, however, the Very Rapid molybdenum(V) e.p.r. signal was obtained. This signal did not change on decreasing the pH, while maintaining the sample in liquid nitrate reductase, caused its molybdenum(V) e.p.r. signal to change from the high-pH to the low-pH form. These findings are not compatible with the conclusions of Edmondson, Ballou, Van Heuvelen, Palmer & Massey [J. Biol. Chem. (1973) 248, 6135-6144], that the Very Rapid signal is in prototropic equilibrium with the Rapid signal, and should be important in understanding the mechanism of action of the enzyme. They emphasize the unique nature of the intermediate represented by the Very Rapid e.p.r. signal. The possible value of the pK for loss of an exchangeable proton from the Rapid signal is discussed.

EPR experiments to elucidate the structure of the ready and unready states of the [NiFe] hydrogenase of Desulfovibrio vulgaris Miyazaki F

2005 ◽  
Vol 33 (1) ◽  
pp. 7-11 ◽  
Author(s):  
M. van Gastel ◽  
C. Fichtner ◽  
F. Neese ◽  
W. Lubitz
Keyword(s):  
Dft Calculations ◽  
Hyperfine Coupling ◽  
Epr Spectra ◽  
Desulfovibrio Vulgaris ◽  
Aerobic Conditions ◽  
Isolation And Purification ◽  
Bridging Ligand ◽  
Exchangeable Proton ◽  
Activation Times ◽  
Epr Experiments

Isolation and purification of the [NiFe] hydrogenase of Desulfovibrio vulgaris Miyazaki F under aerobic conditions leads to a mixture of two states, Ni-A (unready) and Ni-B (ready). The two states are distinguished by different activation times and different EPR spectra. HYSCORE and ENDOR data and DFT calculations show that both states have an exchangeable proton, albeit with a different 1H hyperfine coupling. This proton is assigned to the bridging ligand between Ni and Fe. For Ni-B, a hydroxo ligand is found. For Ni-A, either a hydroxo in a different orientation or a hydroperoxo-bridging ligand is present.

scholarly journals Imaging of Endogenous Exchangeable Proton Signals in the Human Brain Using Frequency Labeled Exchange Transfer Imaging

2013 ◽  
Vol 69 (4) ◽  
pp. 966-973 ◽  
Author(s):  
Nirbhay N. Yadav ◽  
Craig K. Jones ◽  
Jun Hua ◽  
Jiadi Xu ◽  
Peter C. M. van Zijl
Keyword(s):  
Human Brain ◽  
Exchangeable Proton
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