Showing papers on "Electrochemical gradient published in 1976"

Sodium/proton antiport in brush-border-membrane vesicles isolated from rat small intestine and kidney.

Abstract: Studies on proton and Na+ transport by isolated intestinal and renal brush-border-membrane vesicles were carried out to test for the presence of an Na+/H+-exchange system. Proton transport was evaluated as proton transfer from the intravesicular space to the incubation medium by monitoring pH changes in the membrane suspension induced by sudden addition of cations. Na+ transport was determined as Na+ uptake into the vesicles by filtration technique. A sudden addition of sodium salts (but not choline) to the membrane suspension provokes an acidification of the incubation medium which is abolished by the addition of 0.5% Triton X-100. Pretreatment of the membranes with Triton X-100 prevents the acidification. The acidification is also not observed if the [K+] and proton conductance of the membranes have been increased by the simultaneous addition of valinomycin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone to the K+-rich incubation medium. Either valinomycin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone when added alone do not alter the response of the membranes to the addition of Na+. Na+ uptake by brush-border microvilli is enhanced in the presence of a proton gradient directed from the intravesicular space to the incubation medium. Under these conditions a transient accumulation of Na+ inside the vesicles is observed. It is concluded that intestinal and renal brush-border membranes contain a NA+/H+ antiport system which catalyses an electroneutral exchange of Na+ against protons and consequently can produce a proton gradient in the presence of a concentration difference for Na+. This system might be involved in the active proton secretion of the small intestine and the proximal tubule of the kidney.

Transepithelial transport in cell culture

Abstract: In cell culture a kidney epithelial cell line MDCK, forms a continuous sheet of identically oriented asymmetrical cells joined by circumferential occluding junctions. The reconstructed epithelial membrane has transport and permeability qualities of in vivo transporting epithelia. The cell layer can be readily manipulated when cultured on a freely permeable membrane filter and, when placed in an Ussing chamber, electrophysiological measurements can be taken. In the absence of a chemical gradient, the cell layer generates an electrical potential of 1.42 mV, the apical surface negative. It is an effective permeability barrier and lacks significant shunting at the clamped edge, as indicated by a resistance of 84 ohms-cm2, which increased when bulk flow from basolateral to apical was induced by an osmotic gradient or electroosmosis. The MDCK cell layer is cation selective with a relative permeability ratio, PNa/PCl, of 1.7. Net water flux, apical to basolateral, was 7.3 mul cm-2 hr-1 in the absence of a chemical gradient. The morphological and functional qualities of a transporting epithelium are stable in cell culture, and the potential use of a homogeneous cell population in cell culture would enhance studies of epithelial transport at the cellular and subcellular levels.

The Proton Electrochemical Gradient in Escherichia coli Cells

Abstract: The internal pH of Escherichia coli cells was estimated from the distribution of either 5,5-[14C]dimethyl-2,4-oxazolidinedione or [14C]methylamine. EDTA/valinomycin treatment of cells was employed to estimate delta psi from 86Rb+ distribution concomitant with the delta pH for calculation of delta muH. Respiring intact cells maintained an internal pH more alkaline by 0.63-0.75 unit than that of the milieu at extracellular pH 7, both in growth medium and KCl solutions. The delta pH decreased when respiration was inhibited by anaerobiosis or in the presence of KCN. The delta muH, established by EDTA/valinomycin-treated cells, was constant (122-129 mV) over extracellular potassium concentration of 0.01 mM-1 mM. At the lower potassium concentration delta psi (110-120 mV) was the predominant component, and at the higher concentration delta pH increased to 0.7 units (42 mV). At 150 mM potassium delta muH was reduced to 70 mV mostly due to a delta pH component of 0.89 (53 mV). The interchangeability of the delta muH components is consistent with an electronic proton pump and with potassium serving as a counter ion in the presence of valinomycin. Indeed both parameters of delta muH decreased in the presence of carbonylcyanide p-trifluoromethoxyphenylhydrazone. The highest delta pH of 2 units was observed in the intact cells at pH 6; increasing the extracellular pH decreased the delta pH to 0 at pH 7.65 and to -0.51 at pH 9. A similar pattern of dependence of delta pH on extracellular pH was observed in EDTA/valinomycin-treated cells but the delta psi was almost constant over the whole range of extracellular pH values (6-8) implying electroneutral proton movement. Potassium is specifically required for respiration of EDTA-treated E. coli K12 cells since other monovalent or divalent cations could not replace potassium and valinomycin was not required.

The electrochemical gradient of protons and its relationship to active transport in Escherichia coli membrane vesicles.

Abstract: Membrane vesicles isolated from E. coli generate a trans-membrane proton gradient of 2 pH units under appropriate conditions when assayed by flow dialysis. Using the distribution of weak acids to measure the proton gradient (deltapH) and the distribution of the lipophilic cation triphenyl-methylphosphonium to measure the electrical potential across the membrane (delta psi), the vesicles are shown to generate an electrochemical proton gradient (deltamuH+) of approximately-180 mV at pH 5.5 in the presence of ascorbate and phenazine methosulfate, the major component of which is a deltapH of about -110mV. As external pH is increased, deltapH decreases, reaching 0 at pH 7.5 and above, while delta psi remains at about-75 mV and internal pH remains at pH 7.5. Moreover, the ability of various electron donors to drive transport is correlated with their ability to generate deltamuH+. In addition, deltapH and delta psi can be varied reciprocally in the presence of valinomycin and nigericin. These data and others (manuscript in preparation) provide convincing support for the role of chemiosmotic phenomena in active transport.

The calcium conductance of the inner membrane of rat liver mitochondria and the determination of the calcium electrochemical gradient.

Abstract: 1. A method is described for establishing steady-state conditions of calcium transport across the inner membrane of rat liver mitochondria and for determining the current of Ca2+ flowing across the membrane, together with the Ca2+ electrochemical gradient across the native Ca2+ carrier. These parameters were used to quantify the apparent Ca2+ conductance of the native carrier. 2. At 23 degrees C and pH7.0, the apparent Ca2+ conductance of the carrier is close to 1 nmol of Ca2+-min-1-mg of protein-1 mV-1. Proton extrusion by the respiratory chain, rather than the Ca2+ carrier itself, may often be rate-limiting in studies of initial rates of Ca2+ uptake. 3. Under parallel conditions, the endogenous H+ conductance of the membrane is 0.3 nmol of H+-min-1-mg of protein-1-mV-1. 4. Ruthenium Red and La3+ both strongly inhibit the Ca2+ conductance of the carrier, but are without effect on the H+ conductance of the membrane. 5. The apparent Ca2+ conductance of the carrier shows a sigmoidal dependence on the activity of Ca2+ in the medium. At 23 degrees C and pH7.2, half-maximum conductance is obtained at a Ca2+ activity of 4.7 muM. 6. The apparent Ca2+ conductance and the H+ conductance of the inner membrane increase fourfold from 23 degrees to 38 degrees C. The apparent Arrhenius activation energy for Ca2+ transport is 69kJ/mol. The H+ electrochemical gradient maintained in the absence of Ca2+ transport does not vary significantly with temperature. 7. The apparent Ca2+ conductance increases fivefold on increasing the pH of the medium from 6.8 to 8.0. The H+ conductance of the membrane does not vary significantly with pH over this range. 8. Mg2+ has no effect on the apparent Ca2+ conductance when added at concentration up to 1 mM. 9. Results are compared with classical methods of studying Ca2+ transport across the mitochondrial inner membrane.

Bacteriorhodopsin as an Example of a Light-Driven Proton Pump

Abstract: Apart from the long known visual pigments, another retinal protein complex exists in nature, viz. bacteriorhodopsin from halobacteria. In contrast to the visual pigments such as the rhodopsins, which act as light sensors in the eye, bacteriorhodopsin actually transforms light energy. This energy conversion is connected with the asymmetric incorporation of bacteriorhodopsin in the lattice structure of the purple membrane which forms patches on the cell surface of halobacteria. Alongside the chlorophyll system, the purple membrane system represents the second light energy conversion principle to be discovered in living nature. Bacteriorhodopsin acts as a light-driven proton pump or as the main component of such a pump system. Absorption of light triggers off a cycle of reactions coupled with the spatially oriented uptake and release of a proton. In the intact cell an electrochemical gradient is thus built up across the cell membrane of the bacterium in which part of the absorbed light energy is stored and which is not dependent upon redox processes as in the case of respiration or photosynthesis. This electrochemical gradient can supply the energy required for ATP synthesis in the cell; a reversible proton-translocating ATPase serves as catalyst system.

Influence of membrane potential on the sodium-dependent uptake of gamma-aminobutyric acid by presynaptic nerve terminals: experimental observations and theoretical considerations.

Abstract: Sodium, potassium and veratridine were tested for their effects on the uptake of gamma-aminobutyric acid (GABA) by pinched-off presynaptic nerve terminals (synaptosomes). As noted by previous investigators, the uptake from media containing 1 μm GABA (“high-affinity” uptake) is markedly Na-dependent; the uptake averaged 65 pmoles/mg synaptosome protein × min, with [Na]0=145mm and [K]0=5mm, and declined by about 90% when the external Na concentration ([Na]0) was reduced to 13mm (Na replaced by Li). The relationship between [Na]0 and GABA uptake was sigmoid, suggesting that two or more Na+ ions may be required to activate the uptake of one GABA molecule. Thermodynamic considerations indicate that with a Na+/GABA stoichiometry of 2∶1, the Na electrochemical gradient, alone, could provide sufficient energy to maintain a maximum steady-state GABA gradient ([GABA]i/[GABA]0) of about 104 across the plasma membrane of GABA-nergic terminals.

Physiology of Salivary Secretion

Abstract: The aim of the present work was to explain the mechanism of the acinar secretion of the salivary gland during stimulation. The following items were discussed and concluded. (1) The acinus is the majority of cells being the powerful transport system of the fluid from interstitial side to lumen. (2) Osmotic flow was clarified being a cause of water transport, in which the osmolality gradient across the acinus epithelium was initiated by a preceded salt transport. (3) The grades of osmotic gradient, of hydraulic conductivity, and of semipermeable property of gland epithelia were described. (4) On salt transport during stimulation, Na+ inflow across the basal plasma membrane and Na+ extrusion across the luminal membrane of the acinus cell were discussed with respect to the electrochemical gradient and ionic flow. From the electrophysiological work and the ionic distribution of the salivary gland, it is concluded that massive Na+ inflow and K+ outflow across the basal plasma membrane was a passive process due to an increase of permeability to those ion during stimulation, but the process of Na+ extrusion across the plasma membranes of the luminal side of the cell as well as of the secretory granules was active. (5) The electrochemical gradient for Na+ and K+ at the basal plasma membrane which had an important role for passive Na+ and K+ transport may be maintained by ouabain-sensitive Na+-K+ pump as most other cells. (6) A model for salt transport across the acinar cell was proposed. Intracellular Na+ due to passive Na+ inflow may activate cooperatively the Na(Cl) transport system at luminal plasma membrane and membrane of secretory granules in high levels of (Na+)in. Though it also activated the Na+ -K+ transport at the basal plasma membrane in any level of (Na+)in. (7) Energetics for the ion transport of gland was discussed with a transport-work rate equation as well as oxygen consumption in secretory state. It is assumed that the energy in active transport at the luminal plasma membrane requires more than the dissipated energy in passive process at the basal plasma membrane. The energy for active transport across the luminal plasma membrane may be corresponded to a main part of oxygen consumption for ion transport across the overall epithelium. (8) The phenomena of osmotic flow coupling with salt flow and of passive ionic flow coupling with electrochemical gradient which is maintained by Na+ -K+ pump may be an expression of production and utilization of negative entropy which is a characteristic of biological membrane.

Recent studies on the pathophysiology of ischemic cell injury.

Abstract: We can summarize the results of our studies as follows (Fig. 15). The critical cellular factors involved in the loss of reversibility following ischemia appear to be the mechanisms involved in the membrane function of energy transduction. Irreversibility appears to correlate with an irrepairable defect in energy transduction. This could involve both the mitochondrial energy transduction functions and those in the plasma membrane. The mechanisms involved in this transition are not presently clear but they are associated with increased leakiness or permeability of these membranes accompanied by changes in lipid content, alterations in membrane proteins, and presumably in lipid-protein interactions. There are two prominent theories to explain energy transduction. These are the "proton pump" hypothesis of Mitchell (1972) and the "paired moving charge" hypothesis of Blondin and Green (1975). Both of these hypotheses require integrated function of membrane components, i.e., lipid and protein. The hypothesis of Blondin and Green, however, can work even with discontinuous membrane sheets because it involves the concept of ribbons of protein embedded in the protein-lipid membrane matrix. The characteristic finding of our studies following ischemic injury, namely, the continuous electron flow well into the irreversible phase while the energy transduction is impaired, could be explained by both hypotheses. What do these observations have to say about theories of energy conservation? We have observed that the vectorial nature of the proton separation is stopped. Charge separation may not occur at this time across the membrane since proton gradient and possible membrane potential are abolished. Electron transport, however, continues indicating the generation of protons. Since the decline of P/O ratio, decline of proton gradient and the cellular "point-of-no-return" coincide, these observations point toward the important membrane defects acquired at that particular time. The "paired moving charge" model which involves moving ions encapsulated in endogenous ionophores such as lecithin and maintenance of magnesium is favpred by the observation that phosphatidyl choline and phosphatidyl ethanolamine are lost in correlation with irreversibility. Furthermore, the decrease in magnesium content of cells is closely associated with the loss of viability following ischemia. The "paired moving charge" hypothesis has the attractive feature in that it involves antagonistic effects of calcium and magnesium. During reflow, calcium may inhibit magnesium mediated transport of inorganic phosphate by lecithin. Also, according to this theory fatty acids or their cyclic anions which act as uncouplers may foster the loss of phosphorylation capacity.

Equilibrium between two forms of the lac carrier protein in energized and nonenergized membrane vesicles from Escherichia coli.

Abstract: p-Nitrophenyl alpha-D-galactopyranoside is a competitive inhibitor of lactose transport in membrane vesicles prepared from Escherichia coli ML 308-225 (Ki congruent to 6.6 muM) but is not accumulated by the vesicles. Binding of p-nitrophenyl alpha-D-[6-3H]galactopyranoside to membrane vesicles has been measured by flow dialysis. In the presence of D-lactate, ligand binds to the vesicles with a KD of about 6 muM, and a total of 2.3 nmol per mg of membrane protein is bound at saturation. In the absence of D-lactate, a small amount of binding can be detected (approximately 0.2 nmol per mg of membrane protein) with a similar affinity constant (KD congruent to 9 muM). Binding inthe presence or absence of D-lactate is dependent upon a functional lac y gene product and upon the structural integrity of the vesicle membrane and is reversed by p-hydroxymercuribenzenesulfonate. Agents such as 2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, and valinomycin, alone or in combination, abolish D-lactate-dependent binding but do not affect binding in the absence of electron donors. The results confirm previous observations that the bulk of the lac carrier protein is unable to bind ligand unless the membrane is energized. and they also corroborate observations that a small amount of binding occurs in the absence of energy coupling. The findings are discussed in terms of a model in which the lac carrier protein exists in a state of dynamic equilibrium between two forms: (i) a low affinity, cryptic form which predominates in the absence of energy coupling; and (ii) a high affinity form, accessible from the external surface of the membrane, which predominates in the presence of an electrochemical gradient of protons (interior negative and alkaline).

Hamster brown-adipose-tissue mitochondria. The role of fatty acids in the control of the proton conductance of the inner membrane.

Abstract: The specific ability of fatty acids to increase the proton conductance of the inner membrane of mitochondria from the liver and brown adipose tissue of cold-adapted hamsters was compared The liver and brown-adipose-tissue mitochondria had their effective proton conductances increased by respectively 0028 and 094 nmol H+- min-1 (mV of proton electrochemical gradient)-1 for each nmol of palmitate bound No difference could be detected between the abilities of liver and brown-adipose-tissue mitochondria to bind fatty acids Purine nucleotides did not displace farry acids from the brown-adipase-tissue mitochondria The endogenous fatty acid content of hamster brown-adipose-tissue mitochondria prepared in the absence of album was found to be equivalent to 17 +/- 7 nmol of palmitate/mg protein The fatty acid content was reduced to 1 nmol/mg after preincubation of the mitochondria with CoA, ATP and carnitine No inert pool of fatty acids could be detected The endogenous fatty acids of hamster liver mitochondria were less than 4 nmol of palmitate equivalent/mg protein Some of the fatty acid associated with the brown-adipose-tissue mitochondria originates during preparation of the mitochondria In the light of these results, the physiological role of the fatty acids in controlling the proton conductance of the brown-adipose-tissue mitochondrial inner membrane, and hence- non-shivering thermogenesis, is re-evaluated

Influence of unsaturated fatty acids in chloroplasts. Shift of the pH optimum of electron flow and relations to deltapH, thylakoid internal pH and proton uptake.

Abstract: Linolenic acid (C18:3) is the main endogenous unsaturated fatty acid of thylakoid membrane lipids, and seems in its free form to exert significant effects on the structure and function of photosynthetic membranes. In this investigation the effect of linolenic acid was studied at various pH values on the electron flow rate in isolated spinach chloroplasts and related to deltapH, the proton pump and the pH of the inner thylakoid space (pHi). The deltapH and pHi were estimated from the extent of the fluorescence quenching of 9-aminoacridine. Linolenic acid caused a shift (approximately one unit) of the pH optimum for electron flow toward acidity in the following systems: (a) photosystems II + I (from H2O to NADP+ or to 2,6-dichlorophenolindophenol) coupled or non-coupled; (b) photosystem II (from H2O to 2,6-dichlorophenolindophenol in the presence of dibromothymoquinone). In photosystem I conditions (phenazine methosulphate), the deltapH of the control increased as a function of external pHo with a maximum around pH 8.8. When linolenic acid was added, the deltapH dropped, but its optimum was shifted toward more acidic pHo. The same phenomena were also observed in photosytems II + I (from H2O to ferricyanide) and in photosystem II conditions (from H2O to ferricyanide in the presence of dibromothymoquinone). However, the deltapH was smaller and the sensitivity of the proton gradient toward linolenic acid was eventually higher than for photosystem I electron flow activity. The proton pump which might be considered as a measure of the internal buffering capacity of thylakoids was optimum at pHo, 6.7 in the controls. An addition of linolenic acid diminished the proton pump and shifted its optimum toward higher pHo. As a consequence, pHi increased when pHo was raised. At the optimal pHo 8.6 to 9, pHi were 5 to 5.5. Additions of increasing concentrations of linolenic acid displaced the curves toward higher pHi. A decrease of pHo was therefore required to maintain the pHi in the range of 5-5.5 for maximum electron flow. In conclusion, the electron flow activity seems to be delicately controlled by the proton pump (buffer capacity), deltapH, pHi and pHo. Fatty acids damage the membrane integrity in such a way that the subtile equilibrium between the factors is disturbed.

A study of the unidirectional fluxes of Na and Cl across the gills of the dogfish Scyliorhinus canicula (Chondrichthyes)

Abstract: The gills of the dogfish Scyliorhinus canicula are more permeable to Cl than to Na. In sea water, influx of Na and Cl exceeded the efflux of these ions. Under these conditions the fish were slightly electronegative, by about 2 mV, to the external solution. The net accumulation of Cl could be accounted for by diffusion along the observed electrochemical gradient byt the movement of Na into the fish was more consistent with an electrically neutral active Na transport mechanism (using the Ussing flux ratio criterion). When the external pH was was changed from 7-8 to 6-9,, influxes of Na and Cl were depressed, while the effluxes were unaffected, and the fish became slightly less electronegative. In artificial solutions, in which the concentrations of Na and Cl were lowered and replaced with urea to maintain the total osmotic concentration, Na influx displayed saturation kinetics, while Na efflux increased with decreasing Na concentrations. Cl influx decreased linearly, while Cl efflux remained constant. The efflux of Cl could not be reconciled with a process of passive diffusion along any of the observed electrochemical gradients and thus could reflect the presence of an active transport mechanism.

Cell potentials, cell resistance, and proton fluxes in corn root tissue: effects of dithioerythritol

Abstract: Studies were made of the effect of dithioerythritol on net proton flux, potassium influx and efflux, cell potential, and cell resistance in fresh and washed corn ( Zea mays L. WF9XM14) root tissue. Dithioerythritol induces equal proton influx and potassium efflux rates, decreases membrane resistance, and hyperpolarizes the cell potential. Greater effects on H + and K + fluxes are secured at pH 7 than at pH 5. Other sulfhydryl-protecting reagents produced the same responses. No evidence could be found that dithioerythritol affected energy metabolism or membrane ATPase, and proton influx was induced in the presence of uncoupling agents. We deduce that dithioerythritol activates a passive H + /K + antiport, driven in these experiments by the outwardly directed electrochemical gradient of K + . The net effect on H + and K + fluxes is believed to reside with the combined activity of a polarized H + /K + exchanging ATPase and the passive H + /K + antiport. A model is presented to show how the combined system might produce stable potential differences and K + content.

The ins and outs of calcium transport in squid axons: internal and external ion activation of calcium efflux.

Abstract: The intracellular ionized calcium concentration ([Ca2+]i) in squid axons is far below that expected at equilibrium, and Ca2+ must therefore be extruded against a large electrochemical gradient in order to maintain the steady state. In the absence of ATP, Ca efflux from internally-dialyzed axons is largely dependent on external Na, and is associated with a Cai-dependent Na influx. An Nai-dependent Ca influx and Cao-dependent Na efflux have also been observed in squid axons. The data imply that the axolemma has a "carrier" mechanism that can mediate the counterflow exchange of Na+ for Ca2+. Several observations indicate that the stoichiometry of the exchange is about 3 Na+-for-1 Ca2+:a) Ca efflux appears to be a cubic function of external Na concentration; b) Ca efflux is reduced when the membrane is depolarized; and c) the Nao-dependent Ca efflux is about 1.5 pmoles/cm2-sec when free [Ca2+]i is about 160 mum, while the Cai-dependent Na influx is about 5 pmoles/cm2sec. If the stoichiometry is 3-for-1, the Na electrochemical gradient, alone, could provide sufficient energy to maintain [Ca2+]i at about 50-200 nM. ATP also influences the Ca efflux: it appears to increase the affinity of the transport mechanism for internal Ca, but does not affect the maximum velocity of transport. Thus ATP may catalyze, but not necessarily energize Ca transport.

Active transport of calcium across the isolated midgut of Hyalophora cecropia

Abstract: 1. The net flux of 45Ca from lumen to blood side across the isolated and short-circuited Cecropia midgut was 1–9 +/− 0–2 muequiv. cm-2h-1 in 8 mM Ca and the flux ratio was as high as 56 to 1. 2. The calcium influx was depressed by anoxia; 73% after 30 min. 3. The kinetics of Ca transport were anomalous; the apparent Km varied with Ca concentration from less than 0–2 to greater than 5–6 mM Ca and the apparent Vmax varied from less than 1–3 to greater than 3-3 muequiv. cm-2h-1. 4. The calcium influx showed a delay before the tracer steady state was attained, indicating the existence in the transport route of a calcium pool equivalent to 5–7 muequiv/g. wet weight of midgut tissue. 5 High calcium (16 mM) depressed the short-circuit current and potassium transport from blood to lumen side across the midgut. 6. Calcium depressed magnesium transport, from lumen to blood side across the midgut, and magnesium depressed the calcium transport. 7. Ca transport by the midgut does not regulate the Ca level in the haemolymph in vivo; it merely aids the diffusion of calcium down its electrochemical gradient. However, Ca transport may assist the uptake of the nutrients from the midgut contents.

Steady-state calcium fluxes: membrane versus mitochondrial control of ionized calcium in axoplasm.

Abstract: Squid axons appear in a steady state with respect to ionized Ca when [Ca]o is ca. 3 mM and [Ca]i is ca. 30 nM. A membrane pump energized by the Na gradient across the membrane is capable of maintaining this ratio of ionized Ca if four Na enter per Ca extruded. Empirically, it is noted that if the difference between the electrochemical gradient for Na+ and that for Ca2+ is large and positive, Ca efflux is large; for a large but negative difference in the gradient, Ca influx is large. Net fluxes of Ca into the fiber are induced by Na-free solutions or stimulation. These are buffered in axoplasm principally by a high affinity Ca buffer. Mitochondria apparently do not contain large amounts of stored Ca as CN poisoning does not increase ionized Ca in axoplasm if the seawater is Ca-free.

Reconstitution of a proton pump.

Abstract: The retinal-protein complex bacteriorhodopsin mediates lightxnergy conversion in halobacteria. This chromoprotein is embedded in the cell membrane and forms insular regions. These can be isolated by membrane-fractionation procedures, and they consist of a lipid matrix containing bacteriorhodopsin molecules in a hexagonal crystalline arrangement called the purple membrane. Light-absorption by bacteriorhodopsin induces cyclic changes of the molecule accompanied by a vectorial release and uptake of protons. By means of this photochemical cycle an electrochemical proton gradient is created across the cell membrane on illumination, and the gradient energy is used for ATP synthesis inside the cell. A summarizing report on the function of bacteriorhodopsin and this new type of photophosphorylation mediated by it has been given (Oesterhelt, 1976).