scholarly journals Iron-sulphur centres in mitochondria from Arum maculatum spadix with very high rates of cyanide-resistant respiration

1977 ◽  
Vol 166 (3) ◽  
pp. 347-355 ◽  
Author(s):  
R Cammack ◽  
J M Palmer
Keyword(s):  
Succinate Dehydrogenase ◽  
Nadh Dehydrogenase ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
High Rate ◽  
Spin Interaction ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Oxidation Reduction ◽  
Fourth Component ◽  
Arum Maculatum

X-band electron-paramagnetic-resonance spectroscopy at 4.2–77K combined with measurements of oxidation-reduction potential was used to identify iron–sulphur centres in Arum maculatum (cuckoo-pint) mitochondria. In the oxidized state a signal with a derivative maximum at g = 2.02 was assigned to succinate dehydrogenase centre S-3. Unreduced particles showed additional signals at g = 2.04 and 1.98 (at 9.2 GHz), which may be due to a spin-spin interaction. In the reduced state a prominent signal at g = 1.93 and 2.02 was resolved into at least three components that could be assigned to centres S-1 and S-2 of succinate dehydrogenase (midpoint potentials −7 and −240 mV respectively at pH 7.2) and a small amount of centre N-1b (e'o= −240 mV) of NADH-ubiquinone reductase. In addition, changes in line shape around −10 mV indicated the presence of a fourth component in this signal. The latter was more readily reduced by NADH than by succinate, suggesting that it might be associated with the external NADH dehydrogenase. The iron-sulphur centres of NADH-ubiquinone reductase were present in an unusually low concentration, indicating that the alternative, non-phosphorylating, NADH dehydrogenase containing a low number of iron-sulphur centres may be responsible for most of the high rate of oxidation of NADH.

scholarly journals Oxidation--reduction potentials of turkey liver xanthine dehydrogenase and the origins of oxidase and dehydrogenase behaviour in molybdenum-containing hydroxylases

1977 ◽  
Vol 163 (2) ◽  
pp. 279-289 ◽  
Author(s):  
M J Barber ◽  
R C Bray ◽  
R Cammack ◽  
M P Coughlan
Keyword(s):  
Uric Acid ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Xanthine Dehydrogenase ◽  
Resonance Spectroscopy ◽  
Redox Potentials ◽  
Paramagnetic Resonance ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Temperature Electron ◽  
Full Reduction

Redox potentials for the various centres in the enzyme xanthine dehydrogenase (EC 1.2.1.37) from turkey liver determined by potentiometric titration in the presence of mediator dyes, with low-temperature electron-paramagnetic-resonance spectroscopy. Values at 25 degrees C in pyrophosphate buffer, pH 8.2, are: Mo(VI)/Mo(V)(Rapid),-350 +/- 20mV; Mo(V) (Rapid)/Mo(IV), -362 +/- 20mV; Fe-S Iox./Fe-S Ired., -295 +/- 15mV; Fe-S IIox./Fe-S IIred., -292 +/- 15mV; FAD/FADH,-359+-20mV; FADH/FADH2, -366 +/- 20mV. This value of the FADH/FADH2 potential, which is 130mV lower than the corresponding one for milk xanthine oxidase [Cammack, Barber & Bray (1976) Biochem. J. 157, 469-478], accounts for many of the differences between the two enzymes. When allowance is made for some interference by desulpho enzyme, then differences in the enzymes' behaviour in titration with xanthine [Barber, Bray, Lowe & Coughlan (1976) Biochem. J. 153, 297-307] are accounted for by the potentials. Increases in the molybdenum potentials of the enzymes caused by the binding of uric acid are discussed. Though the potential of uric acid/xanthine (-440mV) is favourable for full reduction of the dehydrogenase, nevertheless, during turnover, for kinetic reasons, only FADH and very little FADH2 is produced from it. Since only FADH2 is expected to react with O2, lack of oxidase activity by the dehydrogenase is explained. Reactivity of the two enzymes with NAD+ as electron acceptor is discussed in relation to the potentials.

scholarly journals Oxidation-reduction potentials of molybdenum, flavin and iron-sulphur centres in milk xanthine oxidase

1976 ◽  
Vol 157 (2) ◽  
pp. 469-478 ◽  
Author(s):  
R Cammack ◽  
M J Barber ◽  
R C Bray
Keyword(s):  
Xanthine Oxidase ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Bovine Milk ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Reduction Potentials ◽  
Point Reduction ◽  
Oxidation Reduction ◽  
Mediator System ◽  
Electron Paramagnetic

1. The mid-point reduction potentials of the various groups in xanthine oxidase from bovine milk were determined by potentiometric titration with dithionite in the presence of dye mediators, removing samples for quantification of the reduced species by e.p.r. (electron-paramagnetic-resonance) spectroscopy. The values obtained for the functional enzyme in pyrophosphate buffer, pH8.2, are: Fe/S centre I, −343 +/- 15mV; Fe/S II, −303 +/- 15mV; FAD/FADH-; −351 +/- 20mV; FADH/FADH2, −236 +/-mV; Mo(VI)/Mo(V) (Rapid), −355 +/- 20mV; Mo(V) (Rapid)/Mo(IV), −355 +/- 20mV. 2. Behaviour of the functional enzyme is essentially ideal in Tris but less so in pyrophosphate. In Tris, the potential for Mo(VI)/Mo(V) (Rapid) is lowered relative to that in pyrophosphate, but the potential for Fe/S II is raised. The influence of buffer on the potentials was investigated by partial-reduction experiments with six other buffers. 3. Conversion of the enzyme with cyanide into the non-functional form, which gives the Slow molybdenum signal, or alkylation of FAD, has little effect on the mid-point potentials of the other centres. The potentials associated with the Slow signal are: Mo(VI)/Mo(V) (Slow), −440 +/- 25mV; Mo(V) (Slow)/Mo(IV), −480 +/- 25 mV. This signal exhibits very sluggish equilibration with the mediator system. 4. The deviations from ideal behaviour are discussed in terms of possible binding of buffer ions or anti-co-operative interactions amongst the redox centres.

scholarly journals Electron-paramagnetic-resonance spectroscopy studies of iron-sulphur centres of submitochondrial particles from iron- and sulphur-deficient. Candida utilis

1975 ◽  
Vol 146 (1) ◽  
pp. 239-246 ◽  
Author(s):  
T A Gray ◽  
P B Garland ◽  
D J Lowe ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Nadh Dehydrogenase ◽  
Candida Utilis ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Submitochondrial Particles ◽  
Limited Growth ◽  
Paramagnetic Resonance ◽  
Dehydrogenase Reaction ◽  
Electron Paramagnetic

1. Measurements were made at 12 degrees K of the electron-paramagnetic-resonance (e.p.r.) spectra of submitochondrial particles from Candida utilis cells grown under conditions that alter the amount of the mitochondrial NADH dehydrogenase (EC 1.6.99.3). 2. Iron-limited growth decreases the extent of iron-sulphur e.p.r. signals to undetectable values that are less than 1 percent of those normally found with glycerol-limited growth. 3. Small but significant signals attributable to the NADH dehydrogenase were detected in submitochondrial particles from sulphate-limited cells. 4. Measurements made on submitochondrial particles prepared from these and other phenotypically modified cells lead us to conclude that the presence of low-temperature e.p.r.-detectable iron-sulphur centres attributable to the NADH dehydrogenase are necessary but not sufficient for the coupling of ATP synthesis to the NADH dehydrogenase reaction in the mitochondrial membrane of C. utilis. 6. The amplitude of the g=2.01 signal observed in non-reduced submitochondrial particles is approximately tenfold diminished by iron limitation but not significantly altered by sulphate limitation.

scholarly journals Nitrogenase of Azotobacter chroococcum. Kinetics of the reduction of oxidized iron-protein by sodium dithionite

1976 ◽  
Vol 155 (1) ◽  
pp. 137-144 ◽  
Author(s):  
R N F Thorneley ◽  
M G Yates ◽  
D J Lowe
Keyword(s):  
Electron Paramagnetic Resonance Spectroscopy ◽  
Sodium Dithionite ◽  
Azotobacter Chroococcum ◽  
High Rate ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Fe Protein ◽  
Catalytically Active ◽  
Electron Reduction ◽  
Kinetics Of

The kinetics of the reduction of oxidized Fe-protein of nitrogenase from Azotobacter chroococcum by sodium dithionite were studied by stopped-flow and rapid-freezing e.p.r. (electron-paramagnetic-resonance) spectroscopy. The appearance of the gav. = 1.94 e.p.r. signal (0.24 electron integrated intensity/mol) was associated with a one-electron reduction by SO2- with k greater than 10(8)M-.S-1 at 23 degrees C. A value of k = 1.75s-1 was obtained for the rate of dissociation of S2O42- into 2SO2- at 23 degrees C. Further reductions by SO2- occurred in three slower phases with rate constants in the range 10(4) −10(6)M-1-S-1. These latter phases have no corresponding e.p.r. signal changes and are probably associated with enzymically inactive protein. The high rate of reduction by SO2-of the Fe-protein alone (k greater than 108M1.S-1) relative to the rate of oxidation of the Fe-protein in the catalytically active Fe:Mo-Fe protein complex (k = 2.2 } 102s-1) and the observation that in the steady state the Fe-protein is substantially oxidized means that at normal assay concentrations another reaction must limit the rate of reduction of Fe-protein during turnover.

scholarly journals Tauroursodeoxycholic Acid (TUDCA)—Lipid Interactions and Antioxidant Properties of TUDCA Studied in Model of Photoreceptor Membranes

Membranes ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 327
Author(s):  
Michał J. Sabat ◽  
Anna M. Wiśniewska-Becker ◽  
Michał Markiewicz ◽  
Katarzyna M. Marzec ◽  
Jakub Dybas ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Plasma Membranes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Protective Action ◽  
Antioxidant Properties ◽  
Model Membranes ◽  
Dynamics Simulation ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Tauroursodeoxycholic Acid

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid containing taurine conjugated with the ursodeoxycholic acid (UDCA), has been known and used from ancient times as a therapeutic compound in traditional Chinese medicine. TUDCA has recently been gaining significant interest as a neuroprotective agent, also exploited in the visual disorders. Among several mechanisms of TUDCA’s protective action, its antioxidant activity and stabilizing effect on mitochondrial and plasma membranes are considered. In this work we investigated antioxidant activity of TUDCA and its impact on structural properties of model membranes of different composition using electron paramagnetic resonance spectroscopy and the spin labeling technique. Localization of TUDCA molecules in a pure POPC bilayer has been studied using a molecular dynamics simulation (MD). The obtained results indicate that TUDCA is not an efficient singlet oxygen (1O2 (1Δg)) quencher, and the determined rate constant of its interaction with 1O2 (1Δg) is only 1.9 × 105 M−1s−1. However, in lipid oxidation process induced by a Fenton reaction, TUDCA reveals substantial antioxidant activity significantly decreasing the rate of oxygen consumption in the system studied. In addition, TUDCA induces slight, but noticeable changes in the polarity and fluidity of the investigated model membranes. The results of performed MD simulation correspond very well with the experimental results.

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