![]() As ΔpH increases, the thylakoid lumen becomes more acidic, triggering the q E response, which acts as a photoprotective mechanism by dissipating excess excitation energy from the light harvesting complexes to prevent over-excitation of photosystem II (PSII) ( Müller et al., 2001). Both ΔpH and Δψ drive the synthesis of ATP from ADP and inorganic phosphate (P i) at the chloroplast ATP synthase, but the ΔpH component has additional impact on regulating light capture and electron transfer reactions ( Kramer et al., 2003). The pmf is energetically composed of two components, a proton concentration difference (ΔpH) from the translocation of protons by reduction and reoxidation of plastoquinone and the release of chemical protons from water oxidation-and an electric field (Δψ) from the vectorial transfer of electrons across the transthylakoid membrane ( Avenson et al., 2004). Some of the key regulatory mechanisms involve the electrochemical gradient of protons, or proton motive force ( pmf) across the thylakoid membrane that is generated by light-driven electron transfer reactions through linear electron flow (LEF) and cyclic electron flow (CEF) ( Strand and Kramer, 2014). Plants ameliorate these effects through a series of feedback regulatory mechanisms that decrease the capture of light energy and modulate the transfer of electrons and protons. This regulation is especially critical under conditions where light capture exceeds photosynthetic capacity, and thus leads to buildup of reactive intermediates that can produce deleterious side-reactions, e.g., when light intensity is increased or when metabolism is suppressed under environmental stresses. Oxygenic photosynthesis is the most energetic biological process on earth and thus must be highly regulated to avoid self-destruction. Overall, our results support a critical role for ATP synthase regulation in maintaining photosynthetic control of electron transfer to prevent photodamage. Comparing the current results with previous work on the pgr5 mutant suggests a general mechanism where increased PSI photodamage in both mutants is caused by loss of pmf, rather than inhibition of CEF per se. These conditions favor the accumulation of electrons on the acceptor side of PSI, and result in severe loss of PSI activity. The increased thylakoid proton conductivity (g H +) in cfq results in decreased pmf and lumen acidification, preventing full activation of q E and more rapid electron transfer through the b 6f complex, particularly under low CO 2 and fluctuating light. Here, we show that the cfq mutant of Arabidopsis, harboring single point mutation in its γ-subunit of the chloroplast ATP synthase, increases the specific activity of the ATP synthase and disables its down-regulation under low CO 2. The resulting acidification of the lumen regulates both light harvesting, via the q E mechanism, and photosynthetic electron transfer through the cytochrome b 6f complex. In wild type plants, decreasing CO 2 lowers the activity of the chloroplast ATP synthase, slowing proton efflux from the thylakoid lumen resulting in buildup of thylakoid proton motive force ( pmf). 4Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, USA.3Cell and Molecular Biology, Michigan State University, East Lansing, MI, USA.2Chemistry, Michigan State University, East Lansing, MI, USA.1MSU-DOE Plant Research Lab, Michigan State University, East Lansing, MI, USA.Strand 1 Mio Sato-Cruz 1 Linda Savage 1 Jeffrey A. The return flow of proton down their electrochemical gradient through the enzymatic complex is responsible for the activation of ATPase which drives the synthesis of ATP from ADP and phosphate.Atsuko Kanazawa 1,2 Elisabeth Ostendorf 1 Kaori Kohzuma 1 Donghee Hoh 1,3 Deserah D. This force drives protons across the membrane towards the mitochondrial matrix. The pH gradient and the proton concentration gradient across the inner membrane built a proton motive force. Thus a pH gradient is generated across the inner mitochondrial membrane. The pH of the outer surface of inner mitochondrial membrane lowers considerably due to the concentration of net positive charge. The unidirectional flow of protons towards the outer side results in the accumulation of protons in the intermembrane space. ![]() ![]() Similarly, FADH 2 also transports pairs of protons into the intermembrane space. ![]() Reduced NAD released from Krebs cycle when enter in the electron transport system transports three pairs of protons across the inner mitochondrial membrane to the intermembrane space. The respiratory chain is oriented in such a way that the electrons move in an inward direction and protons flow in an outward direction. The inner mitochondrial membrane is permeable to water but impermeable to protons except at the points where the respiratory chain and ATP synthase are located. ![]()
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