Disease relevance of Photophosphorylation

• The stimulation of photophosphorylation and ATPase by artificial redox mediators in chromatophores of Rhodopseudomonas capsulata at different redox potentials [1].
• The efficiency or reconstitution was measured in thylakoids via the rate of phenazinemethosulfate-mediated cyclic photophosphorylation and in E. coli everted vesicles via the degree of 9-amino-6-chloro-2-methoxyacridine fluorescence quenching [2].
• Analysis of dose-response curves, pH dependence, and estimated membrane concentrations gave a consistent picture of the mechanisms of membrane toxicity: At pH 7, the higher-chlorinated catechols acted as uncouplers of oxidative and photophosphorylation, and the lower-chlorinated catechols and catechol acted as narcotics [3].
• Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na-2S to NADP in Chlorobium chromatophores [4].
• Preillumination of Rhodospirillum rubrum chromatophores with strong, far-red light in the presence of phenazine methosulfate under non-phosphorylation conditions results in a selective, irreversible inactivation (typically about 70%) of photophosphorylation and of uncoupler-stimulated dark ATPase [5].

High impact information on Photophosphorylation

• We conclude that deglycosylated CF1 was unaffected in its ability to bind to the membrane sector of the chloroplast proton-pumping ATPase (CF0) but was altered in some property essential for photophosphorylation but not ATPase activity [6].
• The quantum efficiency of photosynthetic energy conversion was investigated in isolated spinach chloroplasts by measurements of the quantum requirements of ATP formation by cyclic and noncyclic photophosphorylation catalyzed by ferredoxin [7].
• When cyclic and noncyclic photophosphorylation were operating concurrently at 554 nm, a total of about 12 quanta was required to generate the two NADPH and three ATP needed for the assimilation of one CO2 to the level of glucose [7].
• An enrichment for potential photophosphorylation mutants was performed on medium containing arsenate, and acetate-requiring auxotrophs were then identified by replica plating [8].
• In vitro, phenazine methosulfate-dependent photophosphorylation assays revealed that wild-type CF1 exhibits a 2-fold stimulation in the presence of 25 mM DTT, whereas each of the mutant enzymes has activities that are DTT-independent [9].

Biological context of Photophosphorylation

• The formation of CF1 less than ATP, if at the active site of photophosphorylation, means that protonmotive force does not directly promote the synthesis of the beta-gamma phosphoryl bond of ATP during energy-driven ATP synthesis [10].
• Quercetin, an energy transfer inhibitor in photophosphorylation [11].
• At concentrations below 1 mM, hydrophobic pyridine homologues decrease the rate of photophosphorylation and light-stimulated hydrolysis of ATP and light-activated exchange of the tightly bound nucleotides in chloroplasts, but increase the rate of the Hill reaction [12].
• These results indicate a phosphorylation of AMP to ADP being an intermediate step in photophosphorylation [13].
• ATP and pyrophosphate at high concentration (greater than 1 mM) inhibited photophosphorylation of isolated spinach chloroplasts in the normal salt medium and did not cause stimulation of electron transport [14].

Anatomical context of Photophosphorylation

• An unexpected discovery was that the operation of cyclic photophosphorylation by itself was also regulated by a back reaction of NADPH and ferredoxin with two components of chloroplast membranes, component C550 and cytochrome b559 [15].
• At a given value of the transmembrane pH differential, photophosphorylation rates in dithiothreitol-activated thylakoids can be as much as seven to eight times those of nonactivated controls [16].

Associations of Photophosphorylation with chemical compounds

• Under aerobic conditions that are likely to prevail in chloroplasts in vivo, the optimal concentration of ferredoxin for cyclic photophosphorylation was found to be equal to that required for NADP reduction and about one-tenth of that needed for cyclic photophosphorylation under anaerobic conditions [15].
• Similar results are obtained under methyl viologen or phenazine methosulfate/ascorbate-mediated photophosphorylation and are independent of the internal volume of the chloroplasts [17].
• This maleimide, dithiobis-N-ethylmaleimide (DTEM), like another bifunctional maleimide, o-phenylenebismaleimide, is about 500-fold more effective as an inhibitor of photophosphorylation than N-ethylmaleimide [18].
• The preparation no longer served as a coupling factor for photophosphorylation in either EDTA- or silicotungstate-treated chloroplasts [19].
• Influence of adenine nucleotides on the inhibition of photophosphorylation in spinach chloroplasts by N-ethylmaleimide [20].

Gene context of Photophosphorylation

• Two types of kinetic regulation of the activated ATPase in the chloroplast photophosphorylation system [21].
• N-(1-Anilinonaphthyl-4)maleimide (ANM) has been used to modify coupling factor 1 (CF1), the terminal coupling factor of photophosphorylation in chloroplasts [22].
• If the rate of photophosphorylation is partially restricted with the covalent H+-translocating ATP synthase inhibitor dicyclohexylcarbodi-imide, the titre of uncoupler necessary to effect complete inhibition of photophosphorylation is also decreased relative to that in which the covalent H+-ATP synthase inhibitor is absent [23].
• The formation of [beta-32P]ADP during net photophosphorylation is attributable to adenylate kinase action on the [32P]ATP formed since hexokinase and glucose effectively block its production [24].
• Low levels of G6PDH and IDH activities in Het(-) Fix(-) mutant strain further confirmed the lack of heterocyst differentiation and nitrogenase activity in the Het(-) Fix(-) mutant strain.NR, NiR, and GS activities in both the strains were energy-dependent and the energy required is mainly derived from photophosphorylation [25].

References