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Richard W. Hendler Barry Bunow John S. Rieske 《Journal of bioenergetics and biomembranes》1985,17(1):51-64
In coenzyme Q-cycles, it is proposed that one electron from the quinol reduces the Rieske iron sulfur center (E
m280 mV) and the remaining electron on the semiquinone reduces cytochromeb
T (E
m–60 mV). TheE
mfor the two-electron oxidation of the quinol is 60 mV and therefore the reduction of cytochromeb
T by quinol is not favorable. As the stability constant for the dismutation of the semiquinone decreases, the calculatedE
mfor the Q/QH couple is lowered to values below theE
mof cytochromeb
T. Contemporary coenzyme Q-cycles are based on the belief that the lower value for theE
mof the Q/QH couple compared to theE
mfor cytochromeb
T means that the semiquinone is a spontaneous reducing agent for theb-cytochrome. The analysis in the paper shows that this is not necessarily so and that neither binding sites nor ionization of the semiquinoneper se alters this situation. For a Q-cycle mechanism to function,ad hoc provisions must be made to drive the otherwise unfavorable reduction of cytochromeb
T by the semiquinone or for the simultaneous transfer of both electrons to cytochromeb
T and cytochromec
1 (or the iron sulfur protein). Q-cycle mechanisms with these additional provisions can explain the observation thus far accumulated. A linear path which is functionally altered by conformational changes may also explain the data. 相似文献
2.
A successful approach has been developed for the sequencing of apolipoprotein B based upon the procedure of Cleveland et al. [(1977) J. Biol. Chem. 252, 1102-1106] involving limited proteolysis in the presence of sodium dodecyl sulfate. Staphylococcus aureus protease was employed to produce large peptides which were isolated in relatively pure form by preparative gel electrophoresis. Two peptides were partially sequenced using spinning-cup microsequencing techniques. The sequences are: Peptide R2-5, -Ala-Leu-Val-Gly-Ile-Asn- Gly-Glu-Ala-Asn-Leu-Asp-Phe-Leu-Asn-Ile-Pro-Leu-Arg-Ile-Pro-Pro- Met-Arg-(Arg)-; Peptide R3-1, -Leu-Val-Ala-Lys-Pro-Ser-Val-Ser-Val-Glu- Phe-Val-Thr-Asn-Met-Gly-Ile-Ile-Pro-Lys-Phe-Ala-Arg-. Several stretches of residues suitable for the construction of oligonucleotide probes have been identified. 相似文献
3.
(1) Current models for the mechanism of cyclic electron transport in Rhodopseudomonas sphaeroides and Rhodopseudomonas capsulata have been investigated by observing the kinetics of electron transport in the presence of inhibitors, or in photosynthetically incompetent mutant strains. (2) In addition to its well-characterized effect on the Rieske-type iron sulfur center, 5-(n-undecyl)-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) inhibits both cytochrome b50 and cytochrome b?90 reduction induced by flash excitation in Rps. sphaeroides and Rps. capsulata. The concentration dependency of the inhibition in the presence of antimycin (approx. 2.7 mol UHDBT/mol reaction center for 50% inhibition of extent) is very similar to that of its inhibition of the antimycin-insensitive phase of ferricytochrome c re-reduction. UHDBT did not inhibit electron transfer between the reduced primary acceptor ubiquinone (Q?I) and the secondary acceptor ubiquinone (QII) of the reaction center acceptor complex. A mutant of Rps. capsulata, strain R126, lacked both the UHDBT and antimycin-sensitive phases of cytochrome c re-reduction, and ferricytochrome b50 reduction on flash excitation. (3) In the presence of antimycin, the initial rate of cytochrome b50 reduction increased about 10-fold as the Eh(7.0) was lowered below 180 mV. A plot of the rate at the fastest point in each trace against redox potential resembles the Nernst plot for a two-electron carrier with Em(7.0) ≈ 125 ± 15 mV. Following flash excitation there was a lag of 100–500 μs before cytochrome b50 reduction began. However, there was a considerably longer lag before significant reduction of cytochrome c by the antimycin-sensitive pathway occurred. (4) The herbicide ametryne inhibited electron transfer between Q?I and QII. It was an effective inhibitor of cytochrome b50 photoreduction at Eh(7.0) 390 mV, but not at Eh(7.0) 100 mV. At the latter Eh, low concentrations of ametryne inhibited turnover after one flash in only half of the photochemical reaction centers. By analogy with the response to o-phenanthroline, it is suggested that ametryne is ineffective at inhibiting electron transfer from Q?I to the secondary acceptor ubiquinone when the latter is reduced to the semiquinone form before excitation. (5) At Eh(7.0) > 200 mV, antimycin had a marked effect on the cytochrome b50 reduction-oxidation kinetics but not on the cytochrome c and reaction center changes or the slow phase III of the electrochromic carotenoid change on a 10-ms time scale. This observation appears to rule out a mechanism in which cytochrome b50 oxidation is obligatorily and kinetically linked to the antimycin-sensitive phase of cytochrome c reduction in a reaction involving transmembrane charge transfer at high Eh values. However, at lower redox potentials, cytochrome b50 oxidation is more rapid, and may be linked to the antimycin-sensitive reduction of cytochrome c. (6) It is concluded that neither a simple linear scheme nor a simple Q-cycle model can account adequately for all the observations. Future models will have to take account of a possible heterogeneity of redox chains resulting from the two-electron gate at the level of the secondary quinone, and of the involvement of cytochrome b?90 in the rapid reactions of the cyclic electron transfer chain 相似文献
4.
Effect of electron transfer inhibitors on superoxide generation in the cytochrome bc1 site of the mitochondrial respiratory chain 总被引:6,自引:0,他引:6
Antimycin, 2-nonyl-4-hydroxyquinoline N-oxide and funiculosin induce O.2(-) generation by submitochondrial particles oxidizing succinate, whereas KCN, mucidin, myxothiazol or 2,3-dimercaptopropanol inhibit O.2(-) generation. Thenoyltrifluoroacetone does not induce superoxide production by itself but slightly stimulates the reaction initiated by antimycin. The results indicate that auto-oxidation of unstable ubisemiquinone formed in centre o of the Q-cycle generates most of the O.2(-) radicals in the cytochrome bc1-site of the mitochondrial respiratory chain. 相似文献
5.
1. In Rhodopseudomonas sphaeroides the Qx absorption band of the reaction center bacteriochlorophyll dimer which bleaches on photo-oxidation is both blue-shifted and has an increased extinction coefficient on solubilisation of the chromatophore membrane with lauryldimethylamine-N-oxide. These effects may be attributable in part to the particle flattening effect.2. The difference spectrum of photo-oxidisable c type cytochrome in the chromatophore was found to have a slightly variable peak position in the α-band (λmax at 551–551.25 nm); this position was always red-shifted in comparison to that of isolated cytochrome c2 (λmax at 549.5 ± 0.5 nm). The shift in wavelength maximum was not due to association with the reaction center protein. A possible heterogeneity in the c-type cytochromes of chromatophores is discussed.3. Flash-induced difference spectra attributed to cytochrome b were resolved at several different redox potentials and in the presence and absence of antimycin. Under most conditions, one major component, cytochrome b50 appeared to be involved. However, in some circumstances, reduction of a component with the spectral characteristics of cytochrome b?90 was observed.4. Difference spectra attributed to (BChl)2, Q?II, c type cytochrome and cytochrome b50 were resolved in the Soret region for Rhodopseudomonas capsulata.5. A computer-linked kinetic spectrophotometer for obtaining automatically the difference spectra of components functioning in photosynthetic electron transfer chains is described. The system incorporates a novel method for automatically adjusting and holding the photomultiplier supply voltage. 相似文献
6.
The effect of NO between cytochromes b and c of the mitochondrial respiratory chain were studied using submitochondrial particles (SMP) from bovine heart and GSNO and SPER-NO as NO sources. Succinate-cytochrome c reductase (complex II-III) activity (222±4 nmol/min. mg protein) was inhibited by 51% in the presence of 500 μM GSNO and by 48% in the presence of 30 μM SPER-NO, in both cases at ~1.25 μM NO. Neither GSNO nor SPER-NO were able to inhibit succinate-Q reductase activity (complex II; 220±9 nmol/min. mg protein), showing that NO affects complex III. Complex II-III activity was decreased (36%) when SMP were incubated with l-arginine and mtNOS cofactors, indicating that this effect is also produced by endogenous NO. GSNO (500 μM) reduced cytochrome b562 by 71%, in an [O2] independent manner. Hyperbolic increases in O2•- (up to 1.3±0.1 nmol/min. mg protein) and H2O2 (up to 0.64±0.05 nmol/min. mg protein) productions were observed with a maximal effect at 500 μM GSNO. The O2•-/H2O2 ratio was 1.98 in accordance with the stoichiometry of the O2•- disproportionation. Moreover, H2O2 production was increased by 72–74% when heart coupled mitochondria were exposed to 500 μM GSNO or 30 μM SPER-NO. SMP incubated in the presence of succinate showed an EPR signal (g=1.99) compatible with a stable semiquinone. This EPR signal was increased not only by antimycin but also by GSNO and SPER-NO. These signals were not modified under N2 atmosphere, indicating that they are not a consequence to the effect of NOx species on complex III area. These results show that NO interacts with ubiquinone-cytochrome b area producing antimycin-like effects. This behaviour comprises the inhibition of electron transfer, the interruption of the oxidation of cytochromes b, and the enhancement of [UQH•]ss which, in turn, leads to an increase in O2•- and H2O2 mitochondrial production rates. 相似文献
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