Reconstitution of biological molecular generators of electric current. Cytochrome oxidase.

1. Direct measurement of the electric current generation by cytochrome oxidase has been carried out. To this end, two procedures were used. The simpler one consists in formation of planar artificial membrane from the mixture of decane solution of soya bean phospholipids and beef heart cytochrome oxidase. Addition of cytochrome c and ascorbate to one of the two compartments separated by the cytochrome oxidase-containing planar membrane was found to result in a transmembrane electric potential difference being formed (plus on cytochrome c side of the membrane). Maximal values of potential differences obtained by this method were about 40 mV. Much higher potentials were observed when another ("photeoliposome-planar membrane") method was applied. In this case cytochrome oxidase was reconstituted with phospholipid to form proteoliposomes which adhered to planar phospholipid membrane in the presence of Ca2+ ions. Addition of cytochrome c and ascorbate to the proteoliposome-containing compartment gives rise to generation of an electric potential difference across the planar membrane, which reached 100 mV at a current of about 1 X 10(-11) A (minus in the proteoliposome-free compartment). The electromotive force of this generator was estimated as being about 0.2 V. If ascorbate and proteoliposomes were added into different compartments, a penetrating hydrogen atom carrier (phenazine methosulfate, (PMS) or tetramethyl-p-phenylenediamine (TMPD)) was required for a membrane potential to be formed. Generation of an electric potential difference of the opposite direction (plus in the proteoliposome-free compartment) was revealed in experiments with cytochrome oxidase proteoliposome containing cytochrome c in their interior. In this case, addition of PMS or TMPD was necessary. 2. In the suspension of cytochrome oxidase proteoliposome the uptake of a cationic penetrant (tetraphenyl phosphonium cation) was found to be coupled with electron transfer via external cytochrome c. Electron transfer via intraproteoliposomal cytochrome c induced the uptake of anionic penetrants (tetraphenyl borate and phenyldicarbaundecaborane anions). 3. All the above effects were sensitive to cyanide and protonophorous uncouplers. 4. In proteoliposomes containing both cytochrome oxidase and bacteriorhodopsin, the light- and oxidation-dependent generations of membrane potential have been revealed. 5. The data obtained are in agreement with Mitchell's idea of transmembrane electron flow in the cytochrome oxidase segment of the respiratory chain.     

Precursor protein translocation by the Escherichia coli translocase is directed by the protonmotive force.

The SecY/E protein of Escherichia coli was coreconstituted with the proton pump bacteriorhodopsin and cytochrome c oxidase yielding proteoliposomes capable of sustaining a protonmotive force (delta p) of defined polarity and composition. Proteoliposomes support the ATP- and SecA-dependent translocation of proOmpA which is stimulated by a delta p, inside acid and positive. delta p of opposite polarity, inside alkaline and negative, suppresses translocation while SecA-mediated ATP hydrolysis continues unabated. delta psi and delta pH are equally effective in promoting or inhibiting translocation. Membrane-spanning translocation intermediates move backwards in the presence of a reversed delta p. These results support a model [Schiebel, E., Driessen, A.J.M., Hartl, F.-U. and Wickner, W. (1991) Cell, 64, 927-939] in which the delta p defines the direction of translocation after ATP hydrolysis has released proOmpA from its association with SecA. The polarity effect of the delta p challenges models involving delta p-dependent membrane destabilization and provides further evidence for a role of the delta p as driving force in precursor protein translocation.     

Reconstitution of Biological Molecular generators of electric current. Bacteriorhodopsin.

1. Photoinduced generation of electric current by bacteriorhodopsin, incorporated into the planar phospholipid membrane, has been directly measured with conventional electrometer techniques. 2. Two methods for bacteriorhodopsin incorporation have been developed: (a) formation of planar membrane from a mixture of decane solution of phospholipids and of the fraction of violet fragments of the Halobacterium halobium membrane (bacteriorhodopsin sheets), and (b) adhesion of bacteriorhodopsin-containing reconstituted spherical membranes (proteoliposomes) to the planar membrane in the presence of Ca2+ or some other cations. In both cases, illumination was found to induce electric current generation directed across the planar membrane, an effect which was measured by macroelectrodes immersed into electrolyte solutions on both sides of the membrane. 3. The maximal values of the transmembrane electric potential were of about 150 mV at a current of about 10(-11) A. The electromotive force measured by means of counterbalancing the photoeffect by an external battery, was found to reach the value of 300 mV. 4. The action spectrum of the photoeffect coincides with the bacteriorhodopsin absorption spectrum (maximum about 570 nm). 5. Both components of the electrochemical potential of H+ ions (electric potential and delta pH) across the planar membrane affect the bacteriorhodopsin photoelectric response in a fashion which could be expected if bacteriorhodopsin were a light-dependent electrogenic proton pump. 6. La3+ ions were shown to inhibit operation of those bacteriorhodopsin which pump out H+ ions from the La3+-containing compartment. 7. The photoeffect, mediated by proteoliposomes associated with thick planar membrane, is decreased by gramicidin A at concentrations which do not influence the planar membrane resistance in the light. On the contrary, a protonophorous uncoupler, trichlorocarbonylcyanidephenylhydrazone, decreases the photoeffect only if it is added at a concentration lowering the light resistance. The dark resistance is shown to be higher than the light one, and decreases to the light level by gramicidin. 8. A simple equivalent electric scheme consistent with the above results has been proposed.     

Mechanism of action of the peptide antibiotic nisin in liposomes and cytochrome c oxidase-containing proteoliposomes.

The interaction of the peptide antibiotic nisin with liposomes has been studied. The effect of this interaction was analyzed on the membrane potential (inside negative) and the pH gradient (inside alkaline) in liposomes made from Escherichia coli phosphatidylethanolamine and egg phosphatidylcholine (9:1, wt/wt). The membrane potential and pH gradient were generated by artificial ion gradients or by the oxidation of ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine, and cytochrome c by the beef heart cytochrome c oxidase incorporated in the liposomal membranes. Nisin dissipated the membrane potential and the pH gradient in both types of liposomes and inhibited oxygen consumption by cytochrome c oxidase in proteoliposomes. The dissipation of the proton motive force in proteoliposomes was only to a minor extent due to a decrease of the oxidase activity by nisin. The results in these model systems show that a membrane potential and/or a pH gradient across the membrane enhances the activity of nisin. Nisin incorporates into the membrane and makes the membrane permeable for ions. As a result, both the membrane potential and pH gradient are dissipated. The activity of nisin was found to be influenced by the phospholipid composition of the liposomal membrane.     

Mechanism of action of the peptide antibiotic nisin in liposomes and cytochrome c oxidase-containing proteoliposomes.

The interaction of the peptide antibiotic nisin with liposomes has been studied. The effect of this interaction was analyzed on the membrane potential (inside negative) and the pH gradient (inside alkaline) in liposomes made from Escherichia coli phosphatidylethanolamine and egg phosphatidylcholine (9:1, wt/wt). The membrane potential and pH gradient were generated by artificial ion gradients or by the oxidation of ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine, and cytochrome c by the beef heart cytochrome c oxidase incorporated in the liposomal membranes. Nisin dissipated the membrane potential and the pH gradient in both types of liposomes and inhibited oxygen consumption by cytochrome c oxidase in proteoliposomes. The dissipation of the proton motive force in proteoliposomes was only to a minor extent due to a decrease of the oxidase activity by nisin. The results in these model systems show that a membrane potential and/or a pH gradient across the membrane enhances the activity of nisin. Nisin incorporates into the membrane and makes the membrane permeable for ions. As a result, both the membrane potential and pH gradient are dissipated. The activity of nisin was found to be influenced by the phospholipid composition of the liposomal membrane.     

Measurements of the proton motive force generated by cytochrome c oxidase from Bacillus subtilis in proteoliposomes and membrane vesicles

Cytochrome c oxidase from Bacillus subtilis was reconstituted in liposomes and its energy-transducing properties were studied. The reconstitution procedure used included Ca2+-induced fusion of pre-formed membranes. The orientation of the enzyme in liposomes is influenced by the phospholipid composition of the membrane. Negatively charged phospholipids are essential for high oxidase activity and respiratory control. Analyses of the proteoliposomes by gel filtration, density gradient centrifugation and electron microscopy indicated a heterogeneity of the proteoliposomes with respect to size and respiratory control. Cytochrome c oxidase activity in the proteoliposomes resulted in the generation of a proton motive force, internally negative and alkaline. In the presence of the electron donor, ascorbate/N,N,N',N'-tetramethyl-p-phenylenediamine/cytochrome c or ascorbate/phenazine methosulphate, the reconstituted enzyme generated an electrical potential of 84 mV which was increased by the addition of nigericin to 95 mV and a pH gradient of 32 mV which was increased by the addition of valinomycin to 39 mV. Similar results were obtained with beef-heart cytochrome c oxidase reconstituted in liposomes. The maximal proton motive force which could be generated, assuming no endogenous ion leakage, varied over 110-140 mV. From this the efficiency of energy transduction by cytochrome c oxidase was calculated to be 18-23%, indicating that the oxidase is an efficient proton-motive-force-generating system.     

Generation of electric current by chromatophores of Rhodospirillum rubrum and reconstitution of electrogenic function in subchromatophore pigment-protein complexes.

Lipoprotein complexes, containing (1) bacteriochlorophyll reaction centers, (2) bacteriochlorophyll light-harvesting antenna or (3) both reaction centers and antenna, have been isolated from chromatophores of non-sulphur purple bacteria Rhodospirillum rubrum by detergent treatments. The method of reconstituting the proteoliposomes containing these complexes is described. Being associtated with planas azolectin membrane, ptoteoliposomes as well as intact chromatophores were found to generate a light-dependent transmembrane electric potential difference measured by Ag/AgC1 electrodes and voltmeter. The direction of the electric field inproteoliposomes can be regulated by the addition of antenna complexes to the reconstitution mixture. The reaction center complex proteoliposomes generate an electric field of a direction opposite to that in chromatophores, whereas proteoliposomes containing reaction center complexes and a sufficient amount of antenna complexes produce a potential difference as in chromatophores. ATP and inorganic pyrophosphate, besides light, were shown to be usable as energy sources for electric generation in chromatophores associated with planar membrane.     

Generation of electric current by chromatophores of Rhodospirillum rubrum and reconstitution of electrogenic function in subchromatophore pigment-protein complexes

Lipoprotein complexes, containing (1) bacteriochlorophyll reaction centers, (2) bacteriochlorophyll light-harvesting antenna or (3) both reaction centers and antenna, have been isolated from chromatophores of non-sulphur purple bacteria Rhodospirillum rubrum by detergent treatments. The method of reconstituting the proteoliposomes containing these complexes is described. Being associated with planar azolectin membrane, proteoliposomes as well as intact chromatophores were found to generate a light-dependent transmembrane electric potential difference measured by Ag/AgCl electrodes and voltmeter. The direction of the electric field in proteoliposomes can be regulated by the addition of antenna complexes to the reconstitution mixture. The reaction center complex proteoliposomes generate an electric field of a direction opposite to that in chromatophores, whereas proteoliposomes containing reaction center complexes and a sufficient amount of antenna complexes produce a potential difference as in chromatophores. ATP and inorganic pyrophosphate, besides light, were shown to be usable as energy sources for electric generation in chromatophores associated with planar membrane.     

Formation of pH and potential gradients by the reconstituted Azotobacter vinelandii cytochrome bd respiratory protection oxidase.

To directly characterize the bioenergetic properties of the cytochrome bd terminating branch of the Azotobacter vinelandii electron transport chain, the purified cytochrome bd oxidase was reconstituted into a phospholipid environment consisting of phosphatidylethanolamine and phosphatidylglycerol (3:1). The average diameter of the proteoliposomes after extrusion through a polycarbonate membrane was 94 +/- 4 nm. Initiation of respiration upon the addition of 20 microM ubiquinone-1 to proteoliposomes loaded with the pH-sensitive dye pyranine resulted in an immediate alkalization of the vesicle lumen by an average pH change of 0.11 unit. This pH gradient was readily collapsed upon the addition of nigericin, carbonyl cyanide p-(tri-fluoromethoxy) phenyl-hydrazone, gramicidin, Triton X-100, or 2-heptyl-4-hydroxyquinoline N-oxide (HQNO). Proteoliposomal respiration initiated in the presence of the potentiometric membrane dye rhodamine 123 caused the generation of a transmembrane potential; the potential was collapsed upon the addition of either valinomycin or HQNO. The formation of both pH and potential gradients during turnover demonstrates that the A. vinelandii cytochrome bd oxidase is coupled to energy conservation in vivo.     

Mechanism of activation of the chloroplast ATP synthase. A kinetic study of the thiol modulation of isolated ATPase and membrane-bound ATP synthase from spinach by Eschericia coli thioredoxin

The mechanism of thiol modulation of the chloroplast ATP synthase by Escherichia coli thioredoxin was investigated in the isolated ATPase subcomplex and in the ATP synthase complex reconstituted in bacteriorhodopsin proteoliposomes. Thiol modulation was resolved kinetically by continuously monitoring ATP hydrolysis by the isolated subcomplex and ATP synthesis by proteoliposomes. The binding rate constant of reduced thioredoxin to the oxidized ATPase subcomplex devoid of its epsilon subunit could be determined. It did not depend on the catalytic turnover. Reciprocically, the catalytic turnover did not seem to depend on thioredoxin binding. Thiol modulation by Trx of the epsilon-bearing ATPase subcomplex was slow and favored the release of epsilon. The rate constant of thioredoxin binding to the membrane-bound ATP synthase increased with the protonmotive force. It was lower in the presence of ADP than in its absence, revealing a specific effect of the ATP synthase turnover on thioredoxin-gamma subunit interaction. These findings, and more especially the comparisons between the isolated ATPase subcomplex and the ATP synthase complex, can be interpreted in the frame of the rotational catalysis hypothesis. Finally, thiol modulation changed the catalytic properties of the ATP synthase, the kinetics of which became non-Michaelian. This questions the common view about the nature of changes induced by ATP synthase thiol modulation.     

Effect of gangliosides on membrane permeability studied by enzymic and fluorescence-spectroscopy techniques.

The effect of gangliosides on membrane permeability was investigated by studying the kinetic properties of cytochrome c oxidase, the activity of which, when the enzyme is reconstituted in phospholipid vesicles, is dependent on membrane permeability to H+ and K+. The experiments indicate that three different gangliosides (GM1, DD1a, GT1b) incorporated into cytochrome c oxidase-containing phospholipid vesicles stimulate enzymic activity, in the absence of ionophores, most probably by disorganizing the bilayer lipid assembly and increasing its permeability to ions. This interpretation was confirmed by fluorescence-spectroscopy experiments in which the rate of passive leakage of carboxyfluorescein entrapped in the vesicles was measured. Cholera toxin, or its isolated B-subunit, added to GM1-containing proteoliposomes inhibited cytochrome c oxidase activity, indicating the lack of formation, under these experimental conditions, of channels freely permeable to H+ or K+.     

Electrical response of beef-heart submitochondrial particles bound to phospholipid-impregnated millipore filters during ATP hydrolysis

1. Beef heart submitochondrial particles bound to asolectin impregnated Millipore filter, according to the method described earlier (Drachev et al. (1974) Nature 249, 321--324), are able to generate, upon addition of ATP, an electrical potential which can be directly measured. 2. The transmembrane electrical potential generated by ATP hydrolysis reaches values up to 80 mV. The half-time required to attain the plateau of potential is paradoxically long (5 to 10 min at room temperature) and is temperature-dependent. Among different phospholipid species which have been used to impregnate the Millipore filter, phosphatidylethanolamine was found to be the most effective for generation of electrical potential. 3. The potential generated by ATP hydrolysis is inhibited by inhibitors of mitochondrial ATPase, by the uncoupler FCCP and by reagents collapsing the membrane potential. 4. Addition of inhibitors of mitochondrial ATPase, when the plateau of potential is attained, results in a decay of potential. This decay of potential is as slow as the generation of potential induced by ATP hydrolysis. 5. The initial rise in electrical potential is proportional to the ATPase activity.     

Reconstitution of pyrroloquinoline quinone-dependent D-glucose oxidase respiratory chain of Escherichia coli with cytochrome o oxidase.

D-Glucose dehydrogenase is a pyrroloquinoline quinone-dependent primary dehydrogenase linked to the respiratory chain of a wide variety of bacteria. The enzyme exists in the membranes of Escherichia coli, mainly as an apoenzyme which can be activated by the addition of pyrroloquinoline quinone and magnesium. Thus, membrane vesicles of E. coli can oxidize D-glucose to gluconate and generate an electrochemical proton gradient in the presence of pyrroloquinoline quinone. The D-glucose oxidase-respiratory chain was reconstituted into proteoliposomes, which consisted of two proteins purified from E. coli membranes, D-glucose dehydrogenase and cytochrome o oxidase, and E. coli phospholipids containing ubiquinone 8. The electron transfer rate during D-glucose oxidation and the membrane potential generation in the reconstituted proteoliposomes were almost the same as those observed in the membrane vesicles when pyrroloquinoline quinone was added. The results demonstrate that the quinoprotein, D-glucose dehydrogenase, can reduce ubiquinone 8 directly within phospholipid bilayer and that the D-glucose oxidase system of E. coli has a relatively simple respiratory chain consisting of primary dehydrogenase, ubiquinone 8, and a terminal oxidase.     

A mechanism of respiratory control: studies with proteoliposomes containing cytochrome oxidase and bacteriorhodopsin

Both beef heart cytochrome oxidase and bacteriorhodopsin of Halobacterium halobium were reconstituted into liposomes by the sonication-cholate dialysis method. The proteoliposomes showed the respiratory control ratio of 4.2, and steady-state illumination of the vesicles lead to the 2.7-fold stimulation of the oxidase activity in the absence of uncouplers. The light-stimulated state 4 respiration increased with light intensity, but light had no effect on the oxidase activity that had been relieved by addition of uncouplers. Proteoliposomes with the photosensitive oxidase activity were also obtained when cytochrome oxidase vesicles were fused with bacteriorhodopsin vesicles in the presence of calcium chloride, and the extent of photoactivation was maximally 1.4-fold. The light-induced respiratory release was observed even in the presence of valinomycin or nigericin, indicating that the oxidase activity was sensitive to both the membrane potential and the pH gradient. We propose as a mechanism of the respiratory control that the process of proton transport to the reaction center for water formation is the rate limiting step for the cytochrome oxidase activity.     

Simultaneous stimulation of uric acid synthesis and gluconeogenesis in chicken hepatocytes by alpha-adrenergic action of epinephrine and calcium

Formation of a transmembrane electric potential coupled to ATP hydrolysis is demonstrated in chloroplast ATPase complex containing proteoliposomes. The ATP-induced signals were detected through absorbance changes of the membrane potential-responding dye oxonol VI. They were inhibited by the specific energy-transfer inhibitor, tentoxin and the ionophore valinomycin while stimulated by nigericin. Calibration of the transmembrane potential signal was possible by the application of a proton diffusion potential. The ATP-induced transmembrane potential was estimated to be 40–50 mV.     

Hexaammineruthenium as an electron donor to mitochondrial cytochrome oxidase: membrane potential generation in the absence of cytochrome c

Cytochrome c oxidase can generate membrane potential in the absence of cytochrome c (e.g., in cytochrome c-deficient mitochondria or in proteoliposomes) with hexaammineruthenium as an artificial electron donor. Of several other redox mediators tested, phenazine methosulfate was found to be an efficient artificial substrate for membrane energization by cytochrome oxidase, whereas TMPD, DAD, DCPIP or ferrocyanide are virtually ineffective. The ability of Ru(NH3)6(2+) and phenazine methosulfate to support the generation of delta psi by cytochrome c-oxidase correlates with their effectiveness as electron donors to cytochrome a in the cyanide-inhibited membrane-bound enzyme.     

The effect of trypsin treatment on the incorporation and energy-transducing properties of bacteriorhodopsin in liposomes

Bacteriorhodopsin and trypsin-modified bacteriorhodopsin have been reconstituted into liposomes by means of a low pH-sonication procedure. The incorporation of bacteriorhodopsin in these proteoliposomes is predominantly in the same direction as in vivo and the direction of proton pumping is from inside to outside the liposomes. The direction of proton translocation and electrical potential generation was studied as a function of the reconstitution pH. Light-dependent proton extrusion and generation of a Δp, interior negative and alkaline was observed at a reconstitution pH below 3.0 using bacteriorhodopsin, and at a pH below 3.5 using trypsin-modified bacteriorhodopsin. The shift in inflection point is explained in terms of differences between bacteriorhodopsin and trypsin-modified bacteriorhodopsin in a specific protein-phospholipid interaction which depends on the surface charge density of the cytoplasmic side of bacteriorhodopsin. The magnitude of the protonmotive force (Δp) generated by trypsin-modified bacteriorhodopsin in liposomes was quantitated. Illumination of the proteoliposomes resulted in the generation of a high Δp (135 mV, inside negative and alkaline), with a major contribution of the pH gradient. The ionophores nigericin and valinomycin induced, respectively, a compensatory interconversion of ΔpH into Δψ and vice versa. If no endogenous proton permeability of the membrane would exist, a protonmotive force could be generated of − 143 mV as electrical potential alone or − 162 mV as pH gradient alone.     

Proton movements and electric potential generation in reconstituted ATPase proteoliposomes from the thermophilic cyanobacterium Synechococcus 6716

ATP hydrolysis-induced proton translocation and electric potential generation have been studied in ATPase proteoliposomes by means of various optical probes. The proteoliposomes consisted of reconstituted ATPase complex and native lipid mixture isolated from the thermophilic cyanobacterium Synechococcus 6716 [Van Walraven et al. (1983) Eur. J. Biochem. 137, 101-106]. The native cartenoids and added oxonol VI served as probes for the electric membrane potential generated by the net charge separation (negative outside, positive inside). Their responses, with similar half-times as 9-tetradecylamino-6-chloro-2-methoxyacridine, are sensitive to valinomycin and stimulated by nigericin, as expected. The proton concentrations of extraliposomal and intraliposomal aqueous spaces were monitored by neutral red and cresol red; for internal measurements these pH indicators were trapped inside the vesicles during detergent dialysis. Internal acidification and external alkalinization induced by ATP hydrolysis are inhibited by nigericin and enhanced by valinomycin; at the commonly used higher valinomycin concentrations the neutral red response becomes transient, while the much slower cresol red response is diminished right from its onset. At smaller preset pH gradients both ATP hydrolysis activity and neutral red response are diminished. At increasing MgCl2 concentrations the neutral red responses are slowed down and the cresol red responses are slightly enhanced; this is observed for both internal and external dye responses. Neutral red permeation through the membrane is insignificant under our experimental conditions but is enhanced at temperatures below the lipid-phase transition. In the case of externally added neutral red the non-permeant buffer Hepes is only effective at high MgCl2 concentration, whereas some external cresol red response is visible only at high MgCl2 concentration in the presence of Hepes. The kinetics of the pH indicator and electric potential probe responses clearly distinguish fast interfacial and intra-membrane proton displacements from slow bulk proton equilibration. The data are summarized in a model that supports the importance of localized proton displacements for the primary energy-transducing events.     

Proton-motive force-driven D-galactose transport in plasma membrane vesicles from the yeast Kluyveromyces marxianus.

Galactose transport was studied in membrane vesicles, prepared by fusion of plasma membranes from the yeast Kluyveromyces marxianus with proteoliposomes containing beef heart cytochrome c oxidase as a proton-motive force-generating system. Sugar transport studies performed under nonenergized conditions revealed that, even at high protein to phospholipid ratios, not all vesicles contained a D-galactose-specific transporter. The amount of vesicles containing an active carrier proved to be proportional to the amount of plasma membrane protein present in the fusion mixture. By addition of a suitable electron donor system a proton-motive force of -160 mV could be generated, inside alkaline and negative. Moreover, D-galactose accumulation was observed. It was found that D-galactose accumulation was highly dependent on the phospholipid composition of the vesicles, whereas generation of a proton-motive force was not. Best results were obtained with vesicles prepared with Escherichia coli phospholipid, giving a galactose accumulation of 14 times. Uphill transport could be established under conditions where only the pH gradient or the electrical gradient was present. Moreover, kinetic analysis of the galactose transport activity in energized vesicles revealed influx with a Km value of 540 microM, which is in good agreement with the apparent affinity constant obtained with whole cells. These results establish that galactose transport of K. marxianus is a proton-motive force-driven process. Moreover it demonstrates that plasma membrane vesicles co-reconstituted with cytochrome c oxidase are a valuable resource for the analysis of proton-motive force-driven sugar transport systems of yeast.     

Uncoupling Effect of Fatty Acids in Halo- and Alkalotolerant Bacterium Bacillus pseudofirmus FTU

Natural uncouplers of oxidative phosphorylation, long-chain non-esterified fatty acids, cause uncoupling in the alkalo- and halotolerant bacterium Bacillus pseudofirmus FTU. The uncoupling effect in the bacterial cells was manifested as decrease of membrane potential and increase of respiratory activity. The membrane potential decrease was detected only in bacterial cells exhausted by their endogenous substrates. In proteoliposomes containing reconstituted bacterial cytochrome c oxidase, fatty acids caused a "mild" uncoupling effect by reducing membrane potential only at low rate of membrane potential generation. "Free respiration" induced by the "mild" uncouplers, the fatty acids, can be considered as possible mechanism responsible for adaptation of the bacteria to a constantly changed environment.