scholarly journals Voltammetric studies of the reactions of iron–sulphur clusters ([3Fe-4S] or [M3Fe-4S]) formed in Pyrococcus furiosus ferredoxin

1998 ◽  
Vol 335 (2) ◽  
pp. 357-368 ◽  
Author(s):  
Sarah E. J. FAWCETT ◽  
David DAVIS ◽  
Jacques L. BRETON ◽  
Andrew J. THOMSON ◽  
Fraser A. ARMSTRONG
Keyword(s):  
Pyrococcus Furiosus ◽  
Ph Dependence ◽  
Distinct Species ◽  
Bulk Solution ◽  
Protein Film ◽  
Protein Film Voltammetry ◽  
Significant Difference ◽  
The Status ◽  
Wide Ph Range ◽  
Ph Range

Reactions of the [3Fe-4S] cluster and various metallated [M3Fe-4S] adducts co-ordinated in the ferredoxin from the hyperthermophile Pyrococcus furiosus have been studied by protein-film voltammetry, bulk-solution voltammetry, solution kinetics and magnetic CD (MCD). The [3Fe-4S] cluster exhibits two couples, [3Fe-4S]+/0 and [3Fe-4S]0/2-. Film voltammetry is possible over a wide pH range (2–8), revealing that the [3Fe-4S]+/0 couple shows a complex pH dependence with pKred1 = 2.8, pKox = 4.9 and pKred2 = 6.7. From MCD, pKred1 corresponds with protonation of [3Fe-4S]0 to give a spectroscopically distinct species, as reported for ferredoxins from Azotobacterand Sulfolobus. The status of the disulphide/disulphydryl entity makes no significant difference to the data (given for the -S-S- form). Formation of the hyper-reduced [3Fe-4S]2- state is observed, requiring 3H+ for the overall 3e- reduction of [3Fe-4S]+, the change therefore being electroneutral. By comparison with the ferredoxin from Desulfovibrio africanus, uptake of Fe(II) and other M(II) by [3Fe-4S]0 to give [M3Fe-4S] clusters is slow (t1/2 > 10 min at room temperature, slower still if the protein is adsorbed on the electrode), whereas reaction with Tl(I) to produce [Tl3Fe-4S] is very rapid (t1/2 ≪ 1 s), suggesting that co-ordination of Tl does not require reorganization of the protein structure. Rates of formation of [3Fe-4S] from [M3Fe-4S] adducts increase sharply at high potentials, showing that metal release involves a labile ‘super-oxidized ’ [M3Fe-4S]3+ state.

scholarly journals Evaluation of an electrochemical model of erythrocyte pH buffering using 31P nuclear magnetic resonance data.

1990 ◽  
Vol 95 (6) ◽  
pp. 1183-1204 ◽  
Author(s):  
J E Raftos ◽  
B T Bulliman ◽  
P W Kuchel
Keyword(s):  
Cell Volume ◽  
Ph Dependence ◽  
Cell Parameters ◽  
Ph Buffering ◽  
Magnetic Resonance Data ◽  
Wide Ph Range ◽  
Hemoglobin Molecule ◽  
Model Equations ◽  
Nmr Methods ◽  
Ph Range

When erythrocytes are suspended in a solution of known composition the resultant values of such basic cell parameters as volume and pH are difficult to predict. To facilitate such predictions, we developed a mathematical model describing the passive transmembrane distribution of permeant species; three simultaneous equations were produced. Certain essential data required for the model were determined experimentally; these included the pH dependence of the charge on the hemoglobin molecule and the variation of the osmotic coefficient of hemoglobin with cell volume. Finally, cells were added to various solutions, and then titrated to produce a wide pH range (pH 6-8). We measured the resultant cell volume, cellular and extracellular pH using both conventional and 31P NMR methods. The expected equilibrium values of these electrochemical parameters were also calculated by solving (numerically) the three model equations. The accuracy of the model simulations was evaluated by direct comparison of calculated and experimentally determined values.

Kinetics of the interactions between dyes and micelles

1986 ◽  
Vol 64 (5) ◽  
pp. 955-959 ◽  
Author(s):  
Vincent C. Reinsborough ◽  
Josef F. Holzwarth
Keyword(s):  
Hydrophobic Interactions ◽  
Sodium Dodecylsulfate ◽  
Bulk Solution ◽  
Sds Micelles ◽  
Ph Jump ◽  
Wide Ph Range ◽  
Ph Range ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Continuous Flow Method

The rates of association of three azo dyes, methyl red (MR), methyl orange (MO), and pyridine-2-azo-p-dimethylaniline (PADA), with sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles in water were measured at 25 °C over a wide pH range by the continuous flow method of integrating observation (CFMIO). The association was considered in 3 steps: bulk solution encounter, pH jump, and electrostatic and hydrophobic interactions. Either the first or third step is rate limiting depending on the charge of the dye. The rate constant of association of neutral PADA, MR, and MO with SDS micelles is approximately 2 × 106 dm3mol−1s−1 while charging the dyes positively increases k to 109 dm3mol−1 s−1. Increasing the hydrophobicity of dye or micelle increases k for the interaction with the neutral dye species. Changes in k with pH for the dye–CTAB association were less pronounced.

Influence of electrochemical properties in determining the sensitivity of [4Fe-4S] clusters in proteins to oxidative damage

2001 ◽  
Vol 360 (3) ◽  
pp. 717-726 ◽  
Author(s):  
Gareth J. TILLEY ◽  
Raul CAMBA ◽  
Barbara K. BURGESS ◽  
Fraser A. ARMSTRONG
Keyword(s):  
Oxidative Damage ◽  
Structural Changes ◽  
Reduction Potential ◽  
Azotobacter Vinelandii ◽  
Pyrococcus Furiosus ◽  
Protein Film ◽  
Protein Film Voltammetry ◽  
Thauera Aromatica ◽  
Key Factor ◽  
Ferredoxin I

Interconversion between [4Fe-4S] cubane and [3Fe-4S] cuboidal states represents one of the simplest structural changes an iron–sulphur cluster can undertake. This reaction is implicated in oxidative damage and in modulation of the activity and regulation of certain enzymes, and it is therefore important to understand the factors governing cluster stability and the processes that activate cluster conversion. In the present study, protein film voltammetry has been used to induce and monitor the oxidative conversion of [4Fe-4S] into [3Fe-4S] clusters in different variants of Azotobacter vinelandii ferredoxin I (AvFdI; the 8Fe form of the native protein), and ΔThr14/ΔAsp15, Thr14 → Cys (T14C) and C42D mutants. The electrochemical results have been correlated with the differing oxygen sensitivities of [4Fe-4S] clusters, and comparisons have been drawn with other ferredoxins (Desulfovibrio africanus FdIII, Clostridium pasteurianum Fd, Thauera aromatica Fd and Pyrococcus furiosus Fd). In contrast with high-potential iron–sulphur proteins (HiPIPs) for which the oxidized species [4Fe-4S]3+ is inert to degradation and can be isolated, the hypervalent state in these ferredoxins (most obviously the 3+ level) is very labile, and the reduction potential at which this is formed is a key factor in determining the cluster's resistance to oxidative damage.

pH dependence of the electroreduction of nitrate on Rh and Pt polycrystalline electrodes

2014 ◽  
Vol 50 (17) ◽  
pp. 2148-2151 ◽  
Author(s):  
Jian Yang ◽  
Paula Sebastian ◽  
Matteo Duca ◽  
Thijs Hoogenboom ◽  
Marc T. M. Koper
Keyword(s):  
Nitrate Reduction ◽  
Ph Dependence ◽  
Nitrate Anion ◽  
Electrocatalytic Reduction ◽  
Wide Ph Range ◽  
Ph Range

From a study of the electrocatalytic reduction of nitrate on Pt and Rh electrodes over a wide pH range, HNO3 is suggested as the only reducible species in nitrate reduction on Pt, whereas both HNO3 and the nitrate anion are reducible on Rh.

A novel NhaD-type Na+/H+ antiporter from the moderate halophile and alkaliphile Halomonas alkaliphila

2017 ◽  
Vol 63 (7) ◽  
pp. 596-607 ◽  
Author(s):  
Yanhong Wang ◽  
Na Song ◽  
Lina Yang ◽  
Heba Abdel-motaal ◽  
Rui Zhang ◽  
...  
Keyword(s):  
Membrane Vesicles ◽  
Activity Profile ◽  
Moderate Halophile ◽  
E Coli ◽  
Significant Difference ◽  
Dependent Activity ◽  
Wide Ph Range ◽  
Ph Dependent ◽  
Ph Range ◽  
Selection Of

In this study, a NhaD-type Na+/H+ antiporter gene designated Ha-nhaD was obtained by selection of genomic DNA from the moderate halophile and alkaliphile Halomonas alkaliphila in Escherichia coli KNabc lacking 3 major Na+/H+ antiporters. The presence of Ha-NhaD conferred tolerance of E. coli KNabc to NaCl up to 0.6 mol·L–1 and to LiCl up to 0.2 mol·L–1 and to an alkaline pH. pH-dependent Na+(Li+)/H+ antiport activity was detected from everted membrane vesicles prepared from E. coli KNabc/pUC-nhaD but not those of KNabc/pUC18. Ha-NhaD exhibited Na+(Li+)/H+ antiport activity over a wide pH range from 7.0 to 9.5, with the highest activity at pH 9.0. Protein sequence alignment and phylogenetic analysis revealed that Ha-NhaD is significantly different from the 7 known NhaD-type Na+/H+ antiporters, including Dw-NhaD, Dl-NhaD, Vp-NhaD, Vc-NhaD, Aa-NhaD, He-NhaD, and Ha-NhaD1. Although Ha-NhaD showed a closer phylogenetic relationship with Ha-NhaD2, a significant difference in pH-dependent activity profile exists between Ha-NhaD and Ha-NhaD2. Taken together, Ha-nhaD encodes a novel pH-dependent NhaD-type Na+/H+ antiporter.

The Status of Noise Pollution in the Major Traffic Intersections of Khulna Metropolitan City in Bangladesh and its Possible Effect on Noise-Exposed People

2020 ◽  
Vol 1 (5) ◽  
Author(s):  
Aliza Sultana ◽  
Ashok Kumar Paul ◽  
Meher Un Nessa
Keyword(s):  
Noise Level ◽  
Noise Pollution ◽  
Pressure Level ◽  
Pollution Level ◽  
Metropolitan City ◽  
Mixed Area ◽  
Commercial Area ◽  
Significant Difference ◽  
Traffic Intersections ◽  
The Status

This study was conducted in the Khulna metropolitan city to determine the status of noise pollution at major traffic intersections and assess the possible effect of noise on regular noise afflicted people. For this research, five busiest roadways and traffic intersections; two mixed zone and three commercial zones were selected purposively and 'ST-8850 Sound Level Meter' was used to record the noise pressure level. Average noise pressure level and some noise parameters (Leq, L10, L50, L90, and Lnp) were measured at different shifts in each location both on working days and holidays. The result evidently specified that noise level in all major traffic circles of Khulna metropolitan city was much higher than the recommended threshold of acceptable noise level set by the Department of Environment (DOE) of Bangladesh. It was observed that the mixed area (Sonadanga, Gollamari) tends to have a higher average noise level than those of the commercial area (Shibbari, Notunrasta, Dakbangla). The noise pollution level (Lnp) in mixed areas varied from 92.77 dB (A) to 104.74 dB(A) on working days and 86.9 dB(A) to 105.5 dB(A) on holidays. On working days, the highest Leq was observed 92.65 ± 4.15 dB(A) in Sonadanga (mixed area), whereas the lowest was 85.13 ± 2.83 dB(A) in Dakbangla (commercial area). However, on holidays the highest level of Leq was found 90.41 ± 2.25 dB(A) in Sonadanga, while the lowest levels were 80.43 ± 3.20 dB(A) in Dakbangla. One-way ANOVA with LSD post-hoc test results illustrated that on working days there was a significant difference between the noise pollution levels (NPL) in different shifts of day time (F = 8.412, p < .05). The respondents of the study area addressed that they were the most affected by annoyance (70%), headache (62%), and hearing loss (46%) due to regular exposure to the traffic noise. Therefore, it is recommended to enhance awareness regarding the cause and effect of noise pollution among the noise producers and oppressed people. Subsequently, administrative measures have to take to attenuate noise pollution and indemnify the quality health of the citizens.

Status of Family Fissidentaceae in Gujarat

2016 ◽  
Vol 1 (1) ◽  
Author(s):  
D.G. Shah ◽  
D.N. Mehta ◽  
R.V. Gujar
Keyword(s):  
Distinct Species ◽  
The State ◽  
The Other ◽  
Land Plants ◽  
Reproductive Structures ◽  
The Family ◽  
The Status ◽  
Vegetative Characters ◽  
First Time ◽  
Different Parts

Bryophytes are the second largest group of land plants and are also known as the amphibians of the plant kingdom. 67 species of bryophytes have been reported from select locations across the state of Gujrat. The status of family fissidentaceae which is a large moss family is being presented in this paper. Globally the family consists of 10 genera but only one genus, Fissidens Hedw. has been collected from Gujarat. Fissidens is characterized by a unique leaf structure and shows the presence of three distinct lamina, the dorsal, the ventral and the vaginant lamina. A total of 8 species of Fissidens have been reported from the state based on vegetative characters as no sporophyte stages were collected earlier. Species reported from the neighboring states also showed the absence of sporophytes. The identification of different species was difficult due to substantial overlap in vegetative characters. Hence a detailed study on the diversity of members of Fissidentaceae in Gujarat was carried out between November 2013 and February 2015. In present study 8 distinct species of Fissidens have been collected from different parts of the state. Three species Fissidens splachnobryoides Broth., Fissidens zollingerii Mont. and Fissidens curvato-involutus Dixon. have been identified while the other five are still to be identified. Fissidens zollingerii Mont. and Fissidens xiphoides M. Fleisch., which have been reported as distinct species are actually synonyms according to TROPICOS database. The presence of sexual reproductive structures and sporophytes for several Fissidens species are also being reported for the first time from the state.

Polarographic and spectrophotometric behaviour of some N-p-phenyl substituted benzamidines

1991 ◽  
Vol 56 (12) ◽  
pp. 2791-2799 ◽  
Author(s):  
Juan A. Squella ◽  
Luis J. Nuñez-Vergara ◽  
Hernan Rodríguez ◽  
Amelia Márquez ◽  
Jose M. Rodríguez-Mellado ◽  
...  
Keyword(s):  
Spectrophotometric Study ◽  
Absorption Bands ◽  
Electrochemical Parameters ◽  
Wide Ph Range ◽  
Group A ◽  
Substituent Constants ◽  
Ph Range ◽  
The Waves

Five N-p-phenyl substituted benzamidines were studied by DC and DP polarography in a wide pH range. Coulometric results show that the overall processes are four-electron reductions. Logarithmic analysis of the waves indicate that the process are irreversible. The influence of the pH on the polarographic parameters was also studied. A UV spectrophotometric study was performed in the pH range 2-13. In basic media some variations in the absorption bands were observed due to the dissociation of the amidine group. A determination of the pK values was made by deconvolution of the spectra. Correlations of both the electrochemical parameters and spectrophotometric pK values with the Hammett substituent constants were obtained.

Electroanalytical chemistry of vanadium complexes: Electrochemical oxidation of [V(IV)O(nta)(H2O)]-

1989 ◽  
Vol 54 (1) ◽  
pp. 64-69 ◽  
Author(s):  
Roland Meier ◽  
Gerhard Werner ◽  
Matthias Otto
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Oxidation ◽  
Ph Dependence ◽  
Differential Pulse ◽  
Nitrilotriacetic Acid ◽  
Reduced Form ◽  
Vanadium Complexes ◽  
Differential Pulse Polarography ◽  
Electroanalytical Chemistry ◽  
Ph Range

Electrochemical oxidation of [V(IV)O(nta)(H2O)]- (H3nta nitrilotriacetic acid) was studied in aqueous solution by means of cyclic voltammetry, differential pulse polarography, and current sampled DC polarography on mercury as electrode material. In the pH-range under study (5.5-9.0) the corresponding V(V) complex is produced by one-electron oxidation of the parent V(IV) species. The oxidation product is stable within the time scale of cyclic voltammetry. The evaluation of the pH-dependence of the half-wave potentials leads to a pKa value for [V(IV)O(nta)(H2O)]- which is in a good agreement with previous determinations. The measured value for E1/2 is very close to the formal potential E0 calculated via the Nernst equation on the basis of known literature values for log Kox and log Kred, the complex stability constants for the oxidized and reduced form, respectively.

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