scholarly journals Site of inhibition by 2-amino-1,1,3-tricyanopropene of photosynthetic oxygen evolution by spinach leaf chloroplasts (Short Communication)

1973 ◽  
Vol 134 (2) ◽  
pp. 663-665
Author(s):  
E. Margaret Burden ◽  
Alan A. Horton
Keyword(s):  
Steady State ◽  
Short Communication ◽  
O2 Evolution ◽  
Photosynthetic Oxygen Evolution ◽  
Photo Oxidation ◽  
Steady State Fluorescence ◽  
Spinach Leaf ◽  
Photosynthetic O2 Evolution ◽  
Photosynthetic Oxygen ◽  
Spinach Leaves

2-Amino-1,1,3-tricyanopropene inhibits photosynthetic O2 evolution, but, unlike 3-(3,4-dichlorophenyl)-1,1-dimethylurea, has little effect on the steady-state fluorescence of chlorophyll. In chloroplasts prepared from spinach leaves and inhibited by 2-amino-1,1,3-tricyanopropene, a 3-(3,4-dichlorophenyl)-1,1-dimethylurea-sensitive photoreduction of ferricyanide may be restored by addition of semicarbazide. It is concluded that 2-amino-1,1,3-tricyanopropene acts at a point close to the photo-oxidation of water.

Chloride Requirement for Oxygen Evolution in Photosynthesis

1963 ◽  
Vol 18 (9) ◽  
pp. 683-688 ◽  
Author(s):  
J. M. Bové ◽  
Colette Bové ◽  
F. R. Whatley ◽  
Daniel I. Arnon
Keyword(s):  
Oxygen Evolution ◽  
Photochemical Reactions ◽  
Photosynthetic Oxygen Evolution ◽  
Ferricyanide Reduction ◽  
Atp Formation ◽  
Cyclic Photophosphorylation ◽  
Photosynthetic Oxygen ◽  
Isolated Chloroplasts ◽  
Spinach Leaves

The role of chloride in photosynthetic oxygen evolution was reinvestigated by determining the effect of this ion on photochemical reactions of chloroplasts in which oxygen either is or is not produced. The chloroplasts used were isolated from normal spinach leaves. The level of chloride in the reaction mixture was controlled by washing the isolated chloroplasts and by avoiding a chloride contamination from the water and chemicals used. Chloride was found to be essential for each of the photochemical reactions of chloroplasts in which oxygen is produced. These included (a) photoreduction of TPN, (b) photophosphorylation of the noncyclic type in which TPN or ferricyanide reduction is coupled with ATP formation and (c) photophosphorylation of the aerobic, “pseudocyclic” type in which oxygen production occurs but is masked by an equal oxygen consumption. No chloride requirement was found for the anaerobic, cyclic photophosphorylation in which oxygen is not produced. These results support the view that chloride is an essential cofactor for oxygen evolution in photosynthesis.

Photosynthetic Oxygen Exchange in Attached Leaves of C4 Monocotyledons

1982 ◽  
Vol 9 (5) ◽  
pp. 553 ◽  
Author(s):  
RT Furbank ◽  
MR Badger
Keyword(s):  
Malic Enzyme ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Co2 Concentration ◽  
O2 Evolution ◽  
Co2 Uptake ◽  
O2 Uptake ◽  
Co2 Compensation Point ◽  
Uptake Rates ◽  
Photosynthetic O2 Evolution ◽  
Photosynthetic Oxygen

Photosynthetic O2 evolution, O2 uptake and CO2 uptake by intact leaves from plants of the three C4 decarboxylation types were examined using mass-spectrometric gas-exchange and stable isotope techniques. All species showed a relative insensitivity of O2 uptake to CO2 concentration. The uptake rates observed were between 0.2 and 1 nmol O2 cm-2 S-1 at the CO2 compensation point. At ambient external CO2, NADP-malic enzyme type species showed the lowest average O2 uptake, phosphoenolpyruvate carboxykinase types the highest values, and NAD-malic enzyme types showed intermediate values for O2 uptake. These results are discussed in relation to the contributions to O2 uptake of ribulosebisphosphate oxygenase and photoreduction of oxygen.

Spectroscopic Studies of Asparaginyl-tRNA Synthetase from Entamoeba histolytica

2019 ◽  
Vol 26 (6) ◽  
pp. 435-448
Author(s):  
Priyanka Biswas ◽  
Dillip K. Sahu ◽  
Kalyanasis Sahu ◽  
Rajat Banerjee
Keyword(s):  
Circular Dichroism ◽  
Steady State ◽  
Entamoeba Histolytica ◽  
Protein Concentration ◽  
Trna Synthetase ◽  
Solvent Exposure ◽  
Steady State Fluorescence ◽  
State Process ◽  
Wide Range ◽  
Circular Dichroïsm

Background: Aminoacyl-tRNA synthetases play an important role in catalyzing the first step in protein synthesis by attaching the appropriate amino acid to its cognate tRNA which then transported to the growing polypeptide chain. Asparaginyl-tRNA Synthetase (AsnRS) from Brugia malayi, Leishmania major, Thermus thermophilus, Trypanosoma brucei have been shown to play an important role in survival and pathogenesis. Entamoeba histolytica (Ehis) is an anaerobic eukaryotic pathogen that infects the large intestines of humans. It is a major cause of dysentery and has the potential to cause life-threatening abscesses in the liver and other organs making it the second leading cause of parasitic death after malaria. Ehis-AsnRS has not been studied in detail, except the crystal structure determined at 3 Å resolution showing that it is primarily α-helical and dimeric. It is a homodimer, with each 52 kDa monomer consisting of 451 amino acids. It has a relatively short N-terminal as compared to its human and yeast counterparts. Objective: Our study focusses to understand certain structural characteristics of Ehis-AsnRS using biophysical tools to decipher the thermodynamics of unfolding and its binding properties. Methods: Ehis-AsnRS was cloned and expressed in E. coli BL21DE3 cells. Protein purification was performed using Ni-NTA affinity chromatography, following which the protein was used for biophysical studies. Various techniques such as steady-state fluorescence, quenching, circular dichroism, differential scanning fluorimetry, isothermal calorimetry and fluorescence lifetime studies were employed for the conformational characterization of Ehis-AsnRS. Protein concentration for far-UV and near-UV circular dichroism experiments was 8 µM and 20 µM respectively, while 4 µM protein was used for the rest of the experiments. Results: The present study revealed that Ehis-AsnRS undergoes unfolding when subjected to increasing concentration of GdnHCl and the process is reversible. With increasing temperature, it retains its structural compactness up to 45ºC before it unfolds. Steady-state fluorescence, circular dichroism and hydrophobic dye binding experiments cumulatively suggest that Ehis-AsnRS undergoes a two-state transition during unfolding. Shifting of the transition mid-point with increasing protein concentration further illustrate that dissociation and unfolding processes are coupled indicating the absence of any detectable folded monomer. Conclusion: This article indicates that GdnHCl induced denaturation of Ehis-AsnRS is a two – state process and does not involve any intermediate; unfolding occurs directly from native dimer to unfolded monomer. The solvent exposure of the tryptophan residues is biphasic, indicating selective quenching. Ehis-AsnRS also exhibits a structural as well as functional stability over a wide range of pH.

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