1. Requirement for coenzyme Q in plasma membrane electron transport. - Sun, I L; Sun, E E; Crane, F L; Morré, D J; Lindgren, A; Löw, H
Coenzyme Q is required in the electron transport system of rat hepatocyte and human erythrocyte plasma membranes. Extraction of coenzyme Q from the membrane decreases NADH dehydrogenase and NADH:oxygen oxidoreductase activity. Addition of coenzyme Q to the extracted membrane restores the activity. Partial restoration of activity is also found with alpha-tocopherylquinone, but not with vitamin K1. Analogs of coenzyme Q inhibit NADH dehydrogenase and oxidase activity and the inhibition is reversed by added coenzyme Q. Ferricyanide reduction by transmembrane electron transport from HeLa cells is inhibited by coenzyme Q analogs and restored with added coenzyme Q10. Reduction of external ferricyanide...

2. Ferredoxin-1 mRNA is destabilized by changes in photosynthetic electron transport - Petracek, Marie E.; Dickey, Lynn F.; Nguyen, Tuyen T.; Gatz, Christiane; Sowinski, Dolores A.; Allen, George C.; Thompson, William F.
In transgenic tobacco, pea Ferredoxin-1 (Fed-1) mRNA accumulates rapidly in response to photosynthesis even when the transgene is driven by a constitutive promoter. To investigate the role of photosynthesis on Fed-1 mRNA stability, we used the tetracycline repressible Top10 promoter system to specifically shut off transcription of the Fed-1 transgene. The Fed-1 mRNA has a half-life of approximately 2.4 hr in the light and a half-life of only 1.2 hr in the dark or in the presence of the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). These data indicate that cessation of photosynthesis, either by darkness or DCMU results in a...

3. Simultaneous Measurement of ?pH and Electron Transport in Chloroplast Thylakoids by 9-Aminoacridine Fluorescence 12 - Evron, Yoav; McCarty, Richard E.
Electron transport and the electrochemical proton gradient across the thylakoid membrane are two fundamental parameters of photosynthesis. A combination of the electron acceptor, ferricyanide and the ?pH indicator, 9-aminoacridine, was used to measure simultaneously electron transport rates and ?pH solely by changes in the fluorescence of 9-aminoacridine. This method yields values for the rate of electron transport that are comparable with those obtained by established methods. Using this method a relationship between the rate of electron transport and ?pH at various uncoupler concentrations or light intensities was obtained. In addition, the method was used to study the effect of reducing...

4. The Small, Methionine-Rich Chloroplast Heat-Shock Protein Protects Photosystem II Electron Transport during Heat Stress1 - Heckathorn, Scott A.; Downs, Craig A.; Sharkey, Thomas D.; Coleman, James S.
Evidence suggests that the small chloroplast heat-shock protein (Hsp) is involved in plant thermotolerance but its site of action is unknown. Functional disruption of this Hsp using anti-Hsp antibodies or addition of purified Hsp to chloroplasts indicated that (a) this Hsp protects thermolabile photosystem II and, consequently, whole-chain electron transport during heat stress; and (b) this Hsp completely accounted for heat acclimation of electron transport in pre-heat-stressed plants. Therefore, this Hsp is a major adaptation to acute heat stress in plants.

5. The Regulation of Photosynthetic Electron Transport during Nutrient Deprivation in Chlamydomonas reinhardtii1 - Wykoff, Dennis D.; Davies, John P.; Melis, Anastasios; Grossman, Arthur R.
The light-saturated rate of photosynthetic O2 evolution in Chlamydomonas reinhardtii declined by approximately 75% on a per-cell basis after 4 d of P starvation or 1 d of S starvation. Quantitation of the partial reactions of photosynthetic electron transport demonstrated that the light-saturated rate of photosystem (PS) I activity was unaffected by P or S limitation, whereas light-saturated PSII activity was reduced by more than 50%. This decline in PSII activity correlated with a decline in both the maximal quantum efficiency of PSII and the accumulation of the secondary quinone electron acceptor of PSII nonreducing centers (PSII centers capable of...

6. Coenzyme Q reductase from liver plasma membrane: purification and role in trans-plasma-membrane electron transport. - Villalba, J M; Navarro, F; Córdoba, F; Serrano, A; Arroyo, A; Crane, F L; Navas, P
A specific requirement for coenzyme Q in the maintenance of trans-plasma-membrane redox activity is demonstrated. Extraction of coenzyme Q from membranes resulted in inhibition of NADH-ascorbate free radical reductase (trans electron transport), and addition of coenzyme Q10 restored the activity. NADH-cytochrome c oxidoreductase (cis electron transport) did not respond to the coenzyme Q status. Quinone analogs inhibited trans-plasma-membrane redox activity, and the inhibition was reversed by coenzyme Q. A 34-kDa coenzyme Q reductase (p34) has been purified from pig-liver plasma membranes. The isolated enzyme was sensitive to quinone-site inhibitors. p34 catalyzed the NADH-dependent reduction of coenzyme Q10 after reconstitution in...

7. Ascorbate Biosynthesis in Mitochondria Is Linked to the Electron Transport Chain between Complexes III and IV1 - Bartoli, Carlos G.; Pastori, Gabriela M.; Foyer, Christine H.
Ascorbic acid is synthesized from galactono-?-lactone (GL) in plant tissues. An improved extraction procedure involving ammonium sulfate precipitation of membrane proteins from crude leaf homogenates yielded a simple, quick method for determining tissue activities of galactono-?-lactone dehydrogenase (GLDH). Total foliar ascorbate and GLDH activity decreased with leaf age. Subcellular fractionation experiments using marker enzymes demonstrated that 80% of the total GLDH activity was located on the inner mitochondrial membrane, and 20% in the microsomal fraction. Specific antibody raised against potato (Solanum tuberosum L.) tuber GLDH recognized a 56-kD polypeptide in extracts from the mitochondrial membranes but failed to detect the...

8. Relationship between photosynthetic electron transport and pH gradient across the thylakoid membrane in intact leaves. - Schönknecht, G; Neimanis, S; Katona, E; Gerst, U; Heber, U
Under conditions (0.2% CO2; 1% O2) that allow high rates of photosynthesis, chlorophyll fluorescence was measured simultaneously with carbon assimilation at various light intensities in spinach (Spinacia oleracea) leaves. Using a stoichiometry of 3 ATP/CO2 and the known relationship between ATP synthesis rate and driving force (Delta pH), we calculated the light-dependent pH gradient (Delta pH) across the thylakoid membrane in intact leaves. These Delta pH values were correlated with the photochemical (qP) and nonphotochemical (qN) quenching of chlorophyll fluorescence and with the quantum yield of photosystem II (phiPSII). At Delta pH > 2.1 all three parameters (qP, qN, and...

9. Association of glycolate oxidation with photosynthetic electron transport in plant and algal chloroplasts. - Goyal, A; Tolbert, N E
Photosynthetic carbon metabolism is initiated by ribulose-bisphosphate carboxylase/oxygenase (Rubisco), which uses both CO2 and O2 as substrates. One 2-phosphoglycolate (P-glycolate) molecule is produced for each O2 molecule fixed. P-glycolate has been considered to be metabolized exclusively via the oxidative photosynthetic carbon cycle. This paper reports an additional pathway for P-glycolate and glycolate metabolism in the chloroplasts. Light-dependent glycolate or P-glycolate oxidation by osmotically shocked chloroplasts from the algae Dunaliella or spinach leaves was measured by three electron acceptors, methyl viologen (MV), potassium ferricyanide, or dichloroindophenol. Glycolate oxidation was assayed with 3-(3,4)-dichlorophenyl)-1,1-dimethylurea (DCMU) as oxygen uptake in the presence of MV...

10. The Role of Photosynthetic Electron Transport in the Oxidative Degradation of Chloroplastic Glutamine Synthetase1 - Palatnik, Javier F.; Carrillo, Néstor; Valle, Estela M.
The stability of chloroplastic glutamine synthetase (GS; EC 6.3.1.2) was investigated under photooxidative stress using wheat (Triticum aestivum L.) leaves, chloroplasts, and chloroplast lysates. Illuminated seedlings sprayed with the superoxide radical (O2?) propagator methyl viologen showed rapid GS decline dependent on MV concentration and exposure time. Degradation products of approximately 39 and 31 kD were detected when chloroplast lysates containing both stroma and thylakoids were illuminated in the presence of MV or H2O2. In all cases, GS cleavage was prevented by the addition of the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Full protection against degradation could also be obtained by the incorporation...

11. The sulfolipid sulfoquinovosyldiacylglycerol is not required for photosynthetic electron transport in Rhodobacter sphaeroides but enhances growth under phosphate limitation. - Benning, C; Beatty, J T; Prince, R C; Somerville, C R
All photosynthetic organisms, with the exception of several species of photosynthetic bacteria, are thought to contain the sulfolipid 6-sulfo-alpha-D-quinovosyldiacylglycerol. The association of this lipid with photosynthetic membranes has led to the assumption that it plays some role in photosynthesis. Stable null mutants of the photosynthetic bacterium Rhodobacter sphaeroides completely lacking sulfolipid were obtained by disruption of the sqdB gene. The ratios of the various components of the photosynthetic electron transport chain, as well as the electron transfer rates during cyclic electron transport, were not altered in the mutants, when grown under optimal conditions. Growth rates of wild type and mutants...

12. Photosynthetic electron transport controls nitrogen assimilation in cyanobacteria by means of posttranslational modification of the glnB gene product. - Tsinoremas, N F; Castets, A M; Harrison, M A; Allen, J F; Tandeau de Marsac, N
A glnB gene is identified in the cyanobacterium Synechococcus sp. PCC 7942, and its gene product is found to be covalently modified as a result of imbalance in electron transfer in photosynthesis, where photosystem II is favored over photosystem I. The gene was cloned and sequenced and found to encode a polypeptide of 112 amino acid residues, whose sequence shows a high degree of similarity to the Escherichia coli regulatory protein, PII. In E. coli, PII is involved in signal transduction in transcriptional and post-translational regulation of nitrogen assimilation. Increase in ammonium ion concentration is shown to decrease covalent modification...

13. Redox Control of ntcA Gene Expression in Synechocystis sp. PCC 6803. Nitrogen Availability and Electron Transport Regulate the Levels of the NtcA Protein1 - Alfonso, Miguel; Perewoska, Irène; Kirilovsky, Diana
In this work we have studied the influence of the cellular redox status in the expression of the Synechocystis sp. PCC 6803 ntcA gene. Two different ntcA transcripts with different 5? ends were detected, depending on the different dark/light or nitrogen availability conditions. Accumulation of a 0.8-kb ntcA message was light and nitrogen dependent, whereas a longer 1.2-kb ntcA transcript was neither light nor nitrogen regulated. NtcA protein levels increased concomitantly with the accumulation of the 0.8-kb ntcA transcript. The light-dependent accumulation of the ntcA gene and the NtcA protein was sensitive to electron transport inhibitors. In addition, Glc-grown Synechocystis...

14. Relationship between CO2 Assimilation, Photosynthetic Electron Transport, and Active O2 Metabolism in Leaves of Maize in the Field during Periods of Low Temperature1 - Fryer, Michael J.; Andrews, James R.; Oxborough, Kevin; Blowers, David A.; Baker, Neil R.
Measurements of the quantum efficiencies of photosynthetic electron transport through photosystem II (?PSII) and CO2 assimilation (?CO2) were made simultaneously on leaves of maize (Zea mays) crops in the United Kingdom during the early growing season, when chilling conditions were experienced. The activities of a range of enzymes involved with scavenging active O2 species and the levels of key antioxidants were also measured. When leaves were exposed to low temperatures during development, the ratio of ?PSII/?CO2 was elevated, indicating the operation of an alternative sink to CO2 for photosynthetic reducing equivalents. The activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase,...

15. The Role of Chloroplast Electron Transport and Metabolites in Modulating Rubisco Activity in Tobacco. Insights from Transgenic Plants with Reduced Amounts of Cytochrome b/f Complex or Glyceraldehyde 3-Phosphate Dehydrogenase1 - Ruuska, Sari A.; Andrews, T. John; Badger, Murray R.; Price, G. Dean; von Caemmerer, Susanne
Leaf metabolites, adenylates, and Rubisco activation were studied in two transgenic tobacco (Nicotiana tabacum L. cv W38) types. Plants with reduced amounts of cytochrome b/f complex (anti-b/f) have impaired electron transport and a low transthylakoid pH gradient that restrict ATP and NADPH synthesis. Plants with reduced glyceraldehyde 3-phosphate dehydrogenase (anti-GAPDH) have a decreased capacity to use ATP and NADPH in carbon assimilation. The activation of the chloroplast NADP-malate dehydrogenase decreased in anti-b/f plants, indicating a low NADPH/NADP+ ratio. The whole-leaf ATP/ADP in anti-b/f plants was similar to wild type, while it increased in anti-GAPDH plants. In both plant types, the...

16. In Vitro Reconstitution of Electron Transport from Glucose-6-Phosphate and NADPH to Nitrite1 - Jin, Tie; Huppe, Heather C.; Turpin, David H.
An NADPH-dependent NO2?-reducing system was reconstituted in vitro using ferredoxin (Fd) NADP+ oxidoreductase (FNR), Fd, and nitrite reductase (NiR) from the green alga Chlamydomonas reinhardtii. NO2? reduction was dependent on all protein components and was operated under either aerobic or anaerobic conditions. NO2? reduction by this in vitro pathway was inhibited up to 63% by 1 mm NADP+. NADP+ did not affect either methyl viologen-NiR or Fd-NiR activity, indicating that inhibition was mediated through FNR. When NADPH was replaced with a glucose-6-phosphate dehydrogenase (G6PDH)-dependent NADPH-generating system, rates of NO2? reduction reached approximately 10 times that of the NADPH-dependent system. G6PDH...

17. Photosynthetic electron transport in genetically altered photosystem II reaction centers of chloroplasts. - Roffey, R A; Golbeck, J H; Hille, C R; Sayre, R T
Using a cotransformation system to identify chloroplast transformants in Chlamydomonas reinhardtii, we converted histidine-195 of the photosystem II reaction center D1 protein to a tyrosine residue. The mutants were characterized by a reduced quantum efficiency for photosynthetic oxygen evolution, which varied in a pH-dependent manner, a reduced capacity to oxidize artificial donors to photosystem II, and P680+ reduction kinetics (microsecond) that were essentially similar to wild type. In addition, a dark-stable radical was detected by ESR in mutant photosystem II particles but not in wild-type particles. This radical was similar in g value and lineshape to chlorophyll or carotenoid cations...

18. Salicylic Acid Induces Rapid Inhibition of Mitochondrial Electron Transport and Oxidative Phosphorylation in Tobacco Cells1 - Xie, Zhixin; Chen, Zhixiang
Salicylic acid (SA) is known to induce alternative pathway respiration by activating expression of the alternative oxidase gene. In the present study we report a rapid mode of action by SA on plant mitochondrial functions. SA at concentrations as low as 20 ?m induced inhibition of both ATP synthesis and respiratory O2 uptake within minutes of incubation in tobacco (Nicotiana tabacum) cell cultures. Biologically active SA analogs capable of inducing pathogenesis-related genes and enhanced resistance also caused rapid inhibition of ATP synthesis and respiratory O2 uptake, whereas biologically inactive analogs did not. Inhibition of ATP synthesis and respiratory O2 uptake...

19. Behavioral responses of Escherichia coli to changes in redox potential. - Bespalov, V A; Zhulin, I B; Taylor, B L
Escherichia coli bacteria sensed the redox state in their surroundings and they swam to a niche that had a preferred reduction potential. In a spatial redox gradient of benzoquinone/benzoquinol, E. coli cells migrated to form a sharply defined band. Bacteria swimming out of either face of the band tumbled and returned to the preferred conditions at the site of the band. This behavioral response was named redox taxis. Redox molecules, such as substituted quinones, that elicited redox taxis, interact with the bacterial electron transport system, thereby altering electron transport and the proton motive force. The magnitude of the behavioral response...

20. Energy Sources for HCO3? and CO2 Transport in Air-Grown Cells of Synechococcus UTEX 6251 - Li, Qinglin; Canvin, David T.
Light-dependent inorganic C (Ci) transport and accumulation in air-grown cells of Synechococcus UTEX 625 were examined with a mass spectrometer in the presence of inhibitors or artificial electron acceptors of photosynthesis in an attempt to drive CO2 or HCO3? uptake separately by the cyclic or linear electron transport chains. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the cells were able to accumulate an intracellular Ci pool of 20 mm, even though CO2 fixation was completely inhibited, indicating that cyclic electron flow was involved in the Ci-concentrating mechanism. When 200 ?m N,N-dimethyl-p-nitrosoaniline was used to drain electrons from ferredoxin, a similar Ci accumulation...

Página de resultados:
1  2  3  4  5  6  Siguiente