Photosynthetic formation of inorganic pyrophosphate in phototrophic bacteria (original) (raw)

Coupling of proton £ow to ATP synthesis in Rhodobacter capsulatus: F0F1ATP synthase is absent from about half of chromatophores

2001

F0F1-ATP synthase (Há-ATP synthase, F0F1) utilizes the transmembrane protonmotive force to catalyze the formation of ATP from ADP and inorganic phosphate (Pi). Structurally the enzyme consists of a membrane-embedded proton- translocating F0 portion and a protruding hydrophilic F1 part that catalyzes the synthesis of ATP. In photosynthetic purple bacteria a single turnover of the photosynthetic reaction centers (driven by a short saturating flash of light) generates protonmotive force that is sufficiently large to drive ATP synthesis. Using isolated chromatophore vesicles of Rhodobacter capsulatus, we monitored the flash induced ATP synthesis (by chemoluminescence of luciferin/luciferase) in parallel to the transmembrane charge transfer through F0F1 (by following the decay of electrochromic bandshifts of intrinsic carotenoids). With the help of specific inhibitors of F1 (efrapeptin) and of F0 (venturicidin), we decomposed the kinetics of the total proton flow through F0F1 into (i) th...

Demonstration of ΔpH- and Δψ-induced synthesis of inorganic pyrophosphate in chromatophores from Rhodospirillum rubrum

FEBS Letters, 1987

It is possible to obtain synthesis of PPi by artifical ion potentials in Rhodospirillum rubrum chromatophores. PPi can be formed by K +-diffusion gradients (A ~,), H + gradients (ApH) or a combination of both. In contrast, ATP can only be synthesized by imposed A~u or d~,+dpH. For ATP formation there is also a threshold value of K + concentration below which synthesis of ATP is not possible. Such a threshold is not found for PP~ formation. Both PPi and ATP syntheses are abolished by addition of FCCP or nigericin and only marginally affected by electron transport inhibitors. The synthesis of PPi can be monitored for several minutes before it ceases, while ATP production stops within 30 s. As a result the maximal yield of PPi is 200 nmol PPi//tmol BChl, while that of ATP is no more than 25 nmol ATP/Itmol BChl. The initial rates of syntheses were 0.50/tmol PPd/lmol BChl per min and 2.0/tmol ATP/~tmol per min, respectively. These rates are approx. 50 and 20% of the respective photophosphorylation rates under saturating illumination.

Stimulation of ATP Synthesis by a Membrane Potential in Chloroplasts

European Journal of Biochemistry, 1973

Chloroplasts preloaded with protons by light-induced proton uptake do not synthesize ATP in a following dark period if the proton concentration gradient (ApH) is lower than 2.5-3.0 pH units. At such suboptimal ApH values synthesis of ATP can be obtained by imposing a diffusion potential across the chloroplast membrane. This potential was realized by providing a high external concentration of either KC1 in the presence of valinomycin or of NaCl in the presence of monactin. Diffusion-potential-induced stimulation of ATP synthesis was observed both in chloroplasts and in bacterial chromatophores.

Studies on photosynthetic inorganic pyrophosphate formation in Rhodospirillum rubrum chromatophores

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986

Photosynthetic formation of inorganic pyrophosphate (PPi) in RhodospiriUum rubrum chromatophores has been studied utilizing a new and sensitive method for continuous monitoring of PPm synthesis. Studies of the reaction kinetics under a variety of conditions, e.g., at different substrate concentrations and different electron-transport rates, have been performed. At very low light intensities the rate of PPi synthesis is twice the rate of ATP synthesis. Antimycin A, at a concentration which strongly inhibited the photosynthetic ATP formation, inhibited the PPi synthesis much less. Even at low rates of electron transport a significant rate of PPi synthesis is obtained. The rate of photosynthetic ATP formation is stimulated up to 20% when PPI synthesis is inhibited. It is shown that PP~ synthesis and ATP synthesis compete with each other. No inhibition of pyrophosphatase activity is observed at high carbonyl cyanide p-trifluoromethoxyhydrazone concentration while ATPase activity is strongly inhibited under the same conditions.

Energy transduction in photosynthetic bacteria VI. Respiratory sites of energy conservation in membranes from dark-grown cells of Rhodopseudomonas capsulata

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1973

ATPase activity of photosynthetic membrane fragments from the bacterium Rhodopseudomonas capsulata can be stimulated by continuous illumination under conditions of active cyclic electron flow. The activation corresponds to an increase in the maximum velocity of the reaction and does not affect the apparent Km for ATP (o.II raM). No stimulation in the light is observed in the presence of classical uncouplers or oxidized 2,6-dichlorophenolindophenol (DCIP), which, per se, stimulate ATPase in the dark. It is demonstrated, however, that oxidized DCIP acts as an uncoupler of bacterial photophosphorylation.