scholarly journals Studies on the stabilized ubisemiquinone species in the succinate-cytochrome c reductase segment of the intact mitochondrial membrane system

1980 ◽  
Vol 192 (3) ◽  
pp. 769-781 ◽  
Author(s):  
J C Salerno ◽  
T Ohnishi
Keyword(s):  
Redox State ◽  
Ph Dependence ◽  
Specific Inhibitor ◽  
Membrane System ◽  
Dipolar Interaction ◽  
Energy Transduction ◽  
Redox Potentials ◽  
Succinate Cytochrome C Reductase ◽  
Ph Range ◽  
Reduced State

1. Evidence is presented for the presence of a stable ubisemiquinone pair in the vicinity of iron-sulphur centre S-3, based on its thermodynamic and spin relaxation properties. 2. These semiquinones are coupled by dipolar interaction; quantitative analysis of the signals of the spin-coupled semiquinones (at pH 7.4) gives midpoint redox potentials E1 (oxidized to semiquinone state) and E2 (semiquinone to fully reduced state) of 140 and 80mV, respectively, for individual ubiquinones. 3. Values of pKS (pK of the semiquinone form) below 6.5 and pKR (pK of the fully reduced ubiquinone) of about 8.0 or above were estimated from the pH-dependence of the midpoint potentials of the spin coupled signals. Thus the ubisemiquinone associated with succinate dehydrogenase (designated as SQS) functions mostly in the anionic form of the physiological pH range. 4. Theonyltrifluoroacetone, a specific inhibitor of the succinate-ubiquinone reductase segment of the respiratory chain, destabilized the intermediate redox state; thus it quenches both the g = 2.00 signal and ubisemiquinone (SQS) and split signals from the spin coupled pair. This inhibitor has no significant effect on another bound ubisemiquinone species present in the cytochrome bc1 region (designated as SQC). 5. The possible function and location of these stabilized ubisemiquinone species were discussed in connection with Site-II energy transduction.

Some Physicochemical Peculiarities of Poplar Plastocyanins a and b

2009 ◽  
Vol 64 (5-6) ◽  
pp. 399-404 ◽  
Author(s):  
Petya K. Christova ◽  
Anthony A. Donchev ◽  
Alexandra C. Shosheva ◽  
Vladimir I. Getov ◽  
Mitko I. Dimitrov
Keyword(s):  
Plant Species ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
The Other ◽  
Redox Potentials ◽  
Extinction Coefficients ◽  
Structural Differences ◽  
Ph Dependent ◽  
Ph Range ◽  
Reduced Forms

The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectro photometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients ε597, equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron potentials E0′: PCa: ε597 = (4.72 ± 0.08) mM-1 cm-1, Keq = 0.133 ± 0.009, E0′ = (354 ± 11) mV; PCb: ε597 = (5.23 ± 0.16) mM-1 cm-1, Keq = 0.175 ± 0.010, E0′ = (363 ± 12) mV. The pH dependence of the redox potential of PCb was studied too. It was found, that the value of E0′ for PCb is constant in the pH range 6.5 - 9.5, but decreases in the range 4.8 - 6.5. On the whole, the dependence resembles that of PC from some well-known plant species, including poplar PCa. The changes of E0′ in the pH-dependent region for poplar PCb, however, are smaller and are 13 mV per pH unit, whereas in the other well-known plant species the changes are about 50 - 60 mV per pH unit. It has been assumed that the weaker pH dependence of E0′ of PCb accounts for some structural differences between PCa and PCb

The pH Dependence of the Ruthenium-Catalyzed Ferricyanide Oxidation of Cyclohexanol

1989 ◽  
Vol 42 (8) ◽  
pp. 1273 ◽  
Author(s):  
RW Kaziro ◽  
JK Beattie
Keyword(s):  
Aqueous Solutions ◽  
Rate Constant ◽  
Ph Dependence ◽  
Catalytic Cycle ◽  
Ph Range ◽  
Catalyst Lifetime ◽  
Reduced State

The oxidation of cyclohexanol to cyclohexanone by ferricyanide in alkaline aqueous solutions is catalysed by the addition of chlororuthenium compounds. In solutions of pH less than 11 the progress of the reaction is limited by the decomposition of the catalyst in its reduced state. The catalyst lifetime can be lengthened by an increase in the concentration of the ferricyanide oxidant. In solutions of pH 11.3-11.9 either of the oxidation or the reduction steps of the catalytic cycle can be made rate determining, by adjustment of the relative concentrations of cyclohexanol and ferricyanide . The decrease in rate with increase in pH is due to the pH dependence of the reaction of the oxidized catalyst. The rate constant decreases from 26 to 15 dm3 mol-1 s-l between pH 11.3 and 11.9. The rate constant for the ferricyanide oxidation of the reduced catalyst is pH-independent at (6 � 2)×102 dm3 mol-1 s-1 at 298 K, over the same pH range.

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.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

scholarly journals Laccase Redox Potentials: pH Dependence and Mutants, a QM/MM Study

2016 ◽  
Vol 120 (35) ◽  
pp. 9265-9276 ◽  
Author(s):  
Jan P. Götze ◽  
Michael Bühl
Keyword(s):  
Ph Dependence ◽  
Redox Potentials

scholarly journals IMAGING REDOX STATE HETEROGENEITY WITHIN INDIVIDUAL EMBRYONIC STEM CELL COLONIES

2011 ◽  
Vol 04 (03) ◽  
pp. 279-288 ◽  
Author(s):  
HE N. XU ◽  
RUSSELL C. ADDIS ◽  
DAVIDA F. GOINGS ◽  
SHOKO NIOKA ◽  
BRITTON CHANCE ◽  
...  
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Embryonic Stem Cell ◽  
Redox State ◽  
Embryonic Stem ◽  
Reduced Form ◽  
Significant Heterogeneity ◽  
Imaging Data ◽  
Mitochondrial Redox State ◽  
Reduced State

Redox state mediates embryonic stem cell (ESC) differentiation and thus offers an important complementary approach to understanding the pluripotency of stem cells. NADH redox ratio (NADH/(Fp + NADH)), where NADH is the reduced form of nicotinamide adenine dinucleotide and Fp is the oxidized flavoproteins, has been established as a sensitive indicator of mitochondrial redox state. In this paper, we report our redox imaging data on the mitochondrial redox state of mouse ESC (mESC) colonies and the implications thereof. The low-temperature NADH/Fp redox scanner was employed to image mESC colonies grown on a feeder layer of gamma-irradiated mouse embryonic fibroblasts (MEFs) on glass cover slips. The result showed significant heterogeneity in the mitochondrial redox state within individual mESC colonies (size: ~200–440 μm), exhibiting a core with a more reduced state than the periphery. This more reduced state positively correlates with the expression pattern of Oct4, a well-established marker of pluripotency. Our observation is the first to show the heterogeneity in the mitochondrial redox state within a mESC colony, suggesting that mitochondrial redox state should be further investigated as a potential new biomarker for the stemness of embryonic stem cells.

scholarly journals Regulation of gluconeogenesis during exposure of young rats to hypoxic conditions

1971 ◽  
Vol 121 (2) ◽  
pp. 169-178 ◽  
Author(s):  
F. J. Ballard
Keyword(s):  
Steady State ◽  
Concentration Ratio ◽  
Redox State ◽  
Adenine Nucleotides ◽  
Redox Potentials ◽  
Air Content ◽  
Hypoxic Conditions ◽  
Air Atmosphere ◽  
Old Rats ◽  
The Difference

1. Two-day-old rats were exposed at constant temperature to atmospheres containing air and nitrogen with the air content varied in steps from 100 to 0%. By using this system of graded hypoxia a comparison was made between rates of gluconeogenesis from lactate, serine and aspartate in the whole animal and the concentrations of several liver metabolites. 2. Gluconeogenesis, expressed as the percentage incorporation of labelled isotope into glucose plus glycogen, proceeds linearly for 30min when the animals are incubated in a normal air atmosphere, but is completely suppressed if the atmosphere is 100% nitrogen. 3. Preincubation of animals for between 5 and 30min under an atmosphere containing 19% air results in the attainment of a new steady state with respect to gluconeogenesis and hepatic concentrations of ATP, ADP, AMP, lactate, pyruvate, β-hydroxybutyrate and acetoacetate. 4. When lactate (100μmol), aspartate (20μmol) or serine (20μmol) was injected, it was shown that the more severe the hypoxia the greater the depression of gluconeogenesis. Under conditions when gluconeogenesis was markedly inhibited there were no changes in the degree of phosphorylation of hepatic adenine nucleotides, but free [NAD+]/[NADH] ratios fell in both cytosol and mitochondrial compartments of the liver cell. 5. Measurements of total liver NAD+ and NADH showed that the concentrations of these nucleotide coenzymes changed less with anoxia, in comparison with the concentration ratio of free coenzymes. 6. Calculations showed that the difference in NAD+–NADH redox potentials between mitochondrial and cytosol compartments increased with the severity of hypoxia. 7. From the constancy of the concentrations of adenine nucleotides it is concluded that liver of hypoxic rats can conserve ATP by lowering the rate of ATP utilization for gluconeogenesis. Gluconeogenesis may be regulated in turn by the changes in mitochondrial and cytosol redox state.

A nuclear magnetic resonance study of the equilibria and kinetics of the reaction of penicillamine with cystine and related disulfides

1985 ◽  
Vol 63 (8) ◽  
pp. 2225-2231 ◽  
Author(s):  
Yvon Theriault ◽  
Dallas L. Rabenstein
Keyword(s):  
Random Distribution ◽  
Ph Dependence ◽  
Thiol Group ◽  
Nuclear Magnetic Resonance Study ◽  
Mercaptoacetic Acid ◽  
Exchange Reactions ◽  
H Nmr ◽  
Mixed Disulfide ◽  
Ph Range ◽  
Kinetics Of

The thiol/disulfide exchange reactions of penicillamine (PSH) with cystine and several related disulfides (RSSR) have been studied by 1H nmr. The reactions take place in two steps:[Formula: see text]The equilibria and kinetics of the reactions of PSH with cystine were characterized over the pH range 5–8, while the reactions with the disulfides of cysteamine, homocysteine, 2-mercaptoethanol, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptosuccinic acid were studied at neutral pH. From the pH dependence of the rate of the reaction of PSH with cystine, the reactive species are identified as penicillamine with its amino group protonated and its thiol group deprotonated and cystine and penicillamine–cysteine mixed disulfide with their amino groups protonated. For all the disulfides studied, the extent to which the first reaction occurs is within a factor of 2–3 of that predicted by a random distribution, while the extent to which the second reaction occurs is considerably less than for a random distribution. This is attributed to steric effects due to the two methyl groups next to the sulfur of penicillamine.

The mechanism of the nonenzymatic iodination of tyrosine by molecular iodine

1988 ◽  
Vol 66 (9) ◽  
pp. 967-978 ◽  
Author(s):  
H. Brian Dunford ◽  
Adejare J. Adeniran
Keyword(s):  
Ph Dependence ◽  
Acid Catalyst ◽  
Order Rate Constant ◽  
Molecular Iodine ◽  
Base Catalysis ◽  
Slow Step ◽  
Rate Law ◽  
General Acid ◽  
Phenolic Group ◽  
Ph Range

Over the pH range 7–10, at very low buffer concentration, the nonenzymatic iodination of tyrosine obeys the rate law[Formula: see text]where kapp is the measured second order rate constant based upon the total initial concentrations of molecular iodine and tyrosine and K2 (units M) is the equilibrium constant for [Formula: see text]. The value of k′ is 3.5 × 10−8 M∙s−1. There are three plausible mechanisms that fit the experimental data. One, the simplest, is a concerted process in which hypoiodous acid attacks tyrosine with its phenolic group unionized. The other two involve the formation of an iodinated quinoid reactive intermediate species in a rapid pre-equilibrium between unionized tyrosine and either hypoiodous acid or molecular iodine. The pre-equilibrium, if it occurs, favors the initial reactants. It is followed by a slow step in which the quinoid is converted to mono-iodinated tyrosine. Positive deviations from the rate law for pH dependence indicate that some specific acid catalysis (H3O+) is occurring in the pH range 5–7. In the presence of sufficient buffer, general acid–base catalysis is observed with acetic acid acting as a general acid catalyst in the vicinity of pH 5 and carbonate acting as a general base at pH ~ 9.5. The nonenzymatic iodination of tyrosine occurs more rapidly as the pH is increased, in marked contrast to the peroxidase-catalyzed iodination, which has its optimum at low pH.

The reaction of 2,4,6-trinitrobenzene sulfonic acid with pancreatic elastase

1970 ◽  
Vol 48 (11) ◽  
pp. 1249-1259 ◽  
Author(s):  
Leticia Rao ◽  
T. Hofmann
Keyword(s):  
Rate Constant ◽  
Sulfonic Acid ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Trinitrobenzene Sulfonic Acid ◽  
Amino Group ◽  
Tyrosine Residues ◽  
Inactivation Rate Constant ◽  
Lysine Residues ◽  
Ph Range

The reaction of elastase with trinitrobenzene sulfonic acid was investigated in the pH range 9–12. Elastase was found to be inactivated by 2,4,6-trinitrobenzene sulfonic acid. The pH dependence of the pseudo first-order inactivation rate constant showed a pK of 10.3 and gave a Hill plot coefficient of 1.15. Trinitrophenol did not inactivate the enzyme. These results indicate that the inactivation is due to the covalent reaction of trinitrobenzene sulfonic acid with a single group in the enzyme. This group is not the N-terminal since the loss of N-terminal valine was considerably slower than the loss of activity at pH 10.5. The inactivation of elastase with 2,4-dinitrofluorobenzene also showed no correlation with the loss of the N-terminal. When the enzyme was exhaustively treated and fully inactivated with trinitrobenzene sulfonic acid at pH 10.5, the N-terminal valine and two out of three lysine residues were trinitrophenylated. No evidence for the loss of histidine was found. One of the tyrosine residues may be trinitrophenylated as judged from the molar extinction of the trinitrophenylated protein, but it has not been possible to isolate a trinitrophenylated tyrosine-containing peptide. The results can be interpreted in one of two ways: (a) trinitrophenylation of a group with a pK of 10.3, not involved in the activity, inactivates because the introduction of the trinitrophenyl residue causes a denaturation of the enzyme; or (b) a group with a pK of 10.3 controls the active conformation of the enzyme. The results do not exclude the possibility that the N-terminal plays an important role in the activity of the enzyme. Below pH 10.5 the reactivity of the N-terminal is low, indicating that it is buried.At pH 9.0 only the ε-amino group of lysine in position 224 reacted with trinitrobenzene sulfonic acid and full activity was retained. The second-order rate constant for the trinitrophenylation of this group was 25 times higher than that of the ε-amino group of the α-N-benzoyllysine.

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