50 years ago Peter Mitchell proposed the chemiosmotic hypothesis for which he was awarded the Nobel Prize for Chemistry in 1978. His comprehensive review on chemiosmotic coupling known as the first "Grey Book", has been reprinted here with permission, to offer an electronic record and easy access to this important contribution to the biochemical literature. This remarkable account of Peter Mitchell's ideas originally published in 1966 is a landmark and must-read publication for any scientist in the field of bioenergetics. As far as was possible, the wording and format of the original publication have been retained. Some changes were required for consistency with BBA formats though these do not affect scientific meaning. A scanned version of the original publication is also provided as a downloadable file in Supplementary Information and can be found online at doi:10.1016/j.bbabio.2011.09.018. See also Editorial in this issue by Peter R. Rich. Original title: CHEMIOSMOTIC COUPLING IN OXIDATIVE AND PHOTOSYNTHETIC PHOSPHORYLATION, by Peter Mitchell, Glynn Research Laboratories, Bodmin, Cornwall, England.

Chemiosmotic coupling in oxidative and photosynthetic phosphorylation

Hydrogen ion buffers for biological research.

Oxygenic photosynthesis, the principal converter of sunlight into chemical energy on earth, is catalyzed by four multi-subunit membrane-protein complexes: photosystem I (PSI), photosystem II (PSII), the cytochrome b6f complex, and F-ATPase PSI generates the most negative redox potential in nature and largely determines the global amount of enthalpy in living systems PSII generates an oxidant whose redox potential is high enough to enable it to oxidize H2O, a substrate so abundant that it assures a practically unlimited electron source for life on earth During the last century, the sophisticated techniques of spectroscopy, molecular genetics, and biochemistry were used to reveal the structure and function of the two photosystems The new structures of PSI and PSII from cyanobacteria, algae, and plants has shed light not only on the architecture and mechanism of action of these intricate membrane complexes, but also on the evolutionary forces that shaped oxygenic photosynthesis

/pdf/structure-and-function-of-photosystems-i-and-ii-3adv0rc3ct.pdf

Structure and function of photosystems i and ii

In photosynthetic membranes isolated from pea leaves, the redox state of the plastoquinone pool controls both the level of phosphorylation of the chloroplast light-harvesting pigment–protein complex (LHC) and distribution of absorbed excitation energy between the two photosystems. Phosphorylation of LHC polypeptides is proposed as the regulatory mechanism by which photosynthetic systems adapt to changing wavelengths of light.

Chloroplast protein phosphorylation couples plastoquinone redox state to distribution of excitation energy between photosystems

The maintenance of Mg2+ homeostasis in the plant is essential for viability. This review describes Mg2+ functions and balancing in plants, with special focus on the existing knowledge of the involved transport mechanisms. Mg2+ is essential for the function of many cellular enzymes and for the aggregation of ribosomes. Mg2+ concentrations also modulate ionic currents across the chloroplast and the vacuolar membranes, and might thus regulate ion balance in the cell and stomatal opening. The significance of Mg2+ homeostasis has been particularly established with regard to Mg2+'s role in photosynthesis. Mg2+ is the central atom of the chlorophyll molecule, and fluctuations in its levels in the chloroplast regulate the activity of key photosynthetic enzymes. Relatively little is known of the proteins mediating Mg2+ uptake and transport in plants. The plant vacuole seem to play a key role in Mg2+ homeostasis in plant cells. Physiological and molecular evidence indicate that Mg2+ entry to the vacuole is mediated by Mg2+/H+ exchangers. The Arabidopsis vacuolar Mg2+/H+ exchanger, AtMHX, is highly transcribed at the vascular tissue, apparently most abundantly at the xylem parenchyma. Inclusion of Mg2+ ions into the vacuoles of this tissue may determine their partitioning between the various plant organs. Impacts of Mg2+ imbalance are described with respect for both plant physiology and for its nutritional value to animal and human.

Magnesium transport and function in plants: the tip of the iceberg.

Spinach chloroplasts isolated in media containing salts and the rare chloroplasts which are still within their envelopes alike retain grana similar to those seen in chloroplasts in situ.Chloroplasts isolated in low-salt media lose their grana without losing any chlorophyll. These grana-free chloroplasts are considerably swollen and consist almost entirely of continuous sheets of paired-membrane structures. These double structures, the lamellae, are only loosely held together, primarily at the edges, by tenuous material which does not react with permanganate.Addition of salts (methylamine hydrochloride, NaCl, MgCl(2)) to the grana-free low-salt chloroplasts provide strong interlamellar attractions. These attractions result in a stacking of the lamellae which is sometimes almost random but sometimes results in regular structures indistinguishable from the original grana.The phosphorylation-uncoupler atebrin causes further swelling of the chloroplasts in the absence of electron transport by increasing the space between the paired membranes of the lamellae.The rapid electron transport (Hill reaction) made possible by atebrin-uncoupling is associated with a great decrease in chloroplast volume. This decrease results from a collapsing together of the widely separated lamellar membrane pairs. The pairs approach each other so closely that they usually appear as a single membrane when viewed with the electron microscope. The much slower electron transport which occurs in the absence of uncouplers is associated with a similar but smaller decrease in the space between the lamellar membrane pairs.Chloroplasts swell during the rapid electron transport made possible by the phosphorylation-uncoupler methylamine. This swelling is accompanied by a degree of membrane distortion which precludes an interpretation of the mechanism. As with atebrin-faciliated electron transport, obviously paired membranes disappear but it is not yet clear whether this is by association or dissociation of the pairs.

http://www.plantphysiol.org/content/plantphysiol/41/3/544.full.pdf

Effect of Salts and Electron Transport on the Conformation of Isolated Chloroplasts. II. Electron Microscopy

http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/J--Biol--Chem--1971-Saha-3204-9.pdf

Electron Transport and Photophosphorylation in Chloroplasts as a Function of the Electron Acceptor

Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. II. Acceptor-specific inhibition by KCN

Ion movements associated with the pH rise that is observed upon illumination of thylakoid suspensions at low pH have been studied by a multiparameter technique. Light-dependent, dark-reversible fluxes of H+, Cl-, Na+, K+ and divalent cations were monitored, together with simultaneous changes in the optical density of the suspension. Extensive uptake of Cl- and efflux of Mg2+ accompany the apparent inward movement of H+ in the light. Only minor efflux of K+ is seen and Na+ appears immobile. The Cl- and Mg2+ fluxes together compensate for most of the charge transferred as H+, contributing respectively about 49% and 43% on an equivalent basis. The ratio of Cl- influx to Mg2+ efflux is variable, but usually >1.0. The Mg2+ flux can be supplanted by (1) K+ flux, if the K+/Mg2+ activity ratio in the suspension is high, and (2) Ca2+ flux, if the thylakoids are equilibrated with suspending media containing Ca2+. The affinity of the divalentcation-binding sites, or carrier mechanism, is greater for Ca2+ than for Mg2+. Schemes can be drawn up to account for the observed ion movements on the basis of either a chemical or a chemiosmotic mechanism for energy transduction in chloroplasts. In intact chloroplasts, light-dependent control of Mg2+ distribution between thylakoid and stroma could serve to regulate enzyme activities in the carbon fixation pathway, and hence photosynthesis.

https://www.pnas.org/content/pnas/71/4/1484.full.pdf

Seikichi Izawa

Papers

Effect of Salts and Electron Transport on the Conformation of Isolated Chloroplasts. II. Electron Microscopy

Electron Transport and Photophosphorylation in Chloroplasts as a Function of the Electron Acceptor

Electron transport and photophosphorylation in chloroplasts as a function of the electron acceptor. II. Acceptor-specific inhibition by KCN

Light-Dependent Redistribution of Ions in Suspensions of Chloroplast Thylakoid Membranes

The Stoichiometry of Photophosphorylation