scholarly journals Intact Chloroplasts Show Ca2+-Gated Switching between Localized and Delocalized Proton Gradient Energy Coupling (ATP Formation)

1989 ◽  
Vol 90 (4) ◽  
pp. 1513-1523 ◽  
Author(s):  
Gisela G. Chiang ◽  
Richard A. Dilley
Keyword(s):  
Energy Coupling ◽  
Proton Gradient ◽  
Atp Formation ◽  
Intact Chloroplasts ◽  
Gradient Energy

Inhibition of Photosynthetic Reactions by Aureomycin

1984 ◽  
Vol 39 (6) ◽  
pp. 627-633 ◽  
Author(s):  
Ji-yu Ye ◽  
U. Heber
Keyword(s):  
Membrane Potential ◽  
Proton Gradient ◽  
Effective Inhibitor ◽  
Mesophyll Protoplasts ◽  
Electrochromic Shift ◽  
Low Concentrations ◽  
Intact Chloroplasts ◽  
Photosynthetic Reactions ◽  
Isolated Chloroplasts

The effect of aureomycin on photosynthesis was investigated. This antibiotic which has been reported to stimulate photosynthesis at very low concentrations is an effective inhibitor at higher concentrations. In mesophyll protoplasts and isolated chloroplasts from spinach, 50% inhibition of CO2 reduction required about 20 μᴍ aureomycin. The reduction of 3-phosphoglycerate and of oxaloacetate by intact chloroplasts was also inhibited, but not that of nitrite and methylviologen which was actually stimulated. NADP reduction by broken chloroplasts and methylviologen- dependent photophosphorylation were also sensitive to aureomycin. The electrochromic shift at 518 nm which indicates formation of a light-dependent membrane potential was suppressed in the presence of 200 μᴍ aureomycin and the transthylakoid proton gradient was decreased. The data confirm reports that aureomycin has uncoupling properties, and they indicate that it also acts as an inhibitor of ferredoxin/NADP reductase.

CO2 reduction by intact chloroplasts under a diminished proton gradient

1977 ◽  
Vol 461 (1) ◽  
pp. 31-47 ◽  
Author(s):  
Jan-Eric Tillberg ◽  
Christoph Giersch ◽  
Ulrich Heber
Keyword(s):  
Co2 Reduction ◽  
Proton Gradient ◽  
Intact Chloroplasts

Photophosphorylation as Function of ADP Concentration at Varying Transmembrane Proton Gradients

1989 ◽  
Vol 44 (5-6) ◽  
pp. 473-479 ◽  
Author(s):  
Georg Heinen ◽  
Heinrich Strotmann
Keyword(s):  
Steady State ◽  
Kinetic Model ◽  
Light Intensity ◽  
Phosphate Concentration ◽  
Proton Gradient ◽  
Enzyme Kinetic ◽  
Fluorescence Technique ◽  
Proton Gradients ◽  
Atp Formation ◽  
External Ph

Abstract Rates of photophosphorylation were measured at constant saturating phosphate concentration , varying ADP concentration , and varying light intensity. As the transmembrane proton gradient is decreased by phosphorylation to different extents depending on the concentration of ADP . rates of ATP formation obtained at the different ADP concentrations were plotted versus the actual steady state ΔpH (in the absence of ΔΨ) during the course of the reaction . ΔpH was monitored by the calibrated 9-aminoacridine fluorescence technique. In secondary plots phosphorylation as function of ADP concentration at different constant ΔpH values were obtained . The results indicate Michaelis-Menten kinetics. The true Km for ADP is virtually unaffected by ΔpH whereas Vmax (at ADP saturation ) strongly depends on ΔpH . The results are discussed in the framework of a simple enzyme kinetic model which considers the intrathylakoidal proton (at constant external pH ) as a third substrate for ATP formation. The model is capable o f explaining the reported results as well as a variety of important results from the literature.

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