Valerij Sokolov - Academia.edu (original) (raw)
Papers by Valerij Sokolov
Biochemistry (Moscow) Supplement Series A: Membrane and Cell Biology, 2010
The effect of pH on electrogenic sodium transport by the Na+ ,K+ -ATPase has been studied. Experi... more The effect of pH on electrogenic sodium transport by the Na+ ,K+ -ATPase has been studied. Experiments were carried out by admittance recording in a model system consisting of a bilayer lipid membrane with adsorbed membrane fragments containing purified Na+ ,K+ -ATPase. Changes in the membrane admittance (capacitance and conductance increments in response to photo-induced release of ATP from caged ATP) were measured as function of AC voltage frequency, sodium ion concentration, and pH. In solutions containing 150 m M Na+, the frequency dependence of capacitance increments was not significantly dependent on pH in the range between 6 and 8. At a low NaCl concentration (3 mM), the capacitance increments at low frequencies decreased with the increasing pH. In the absence ofNaCl, the frequency-dependent capacitance increment at low frequencies was similar to that measured in the presence of 3 mM NaCI. These results may be explained by involvement of protons in the Na+, K+ -ATPase pump cycle, i.e., electroneutral exchange of sodium ions for protons under physiological conditions, electrogenic transport of sodium ions at high pH, and electrogenic transport of protons at low concentrations (and in the absence) of sodium ions.
Biologicheskie Membrany, 2007
European Biophysics Journal, 2019
Biophysical Journal, 2020
Acta physiologica Scandinavica. Supplementum, 1998
The complex functions of the Na,K-ATPase can be described by reaction cycles based on the general... more The complex functions of the Na,K-ATPase can be described by reaction cycles based on the generally accepted "Post-Albers cycle". By appropriate experimental conditions various, partly overlapping partial reactions may be isolated which allow the investigation of specific reaction steps and their succession. From kinetic analysis rate constants and dielectric properties may be determined which characterize the function of the ion pump and allow the formulation of constraints with respect to structure-function relations. This is exemplified by two partial reactions which comprise (1) the ATP-driven Na+ transport, and (2) binding of Na+ ions to the cytoplasm sites. Equilibrium Na+ titration experiments were performed using the fluorescent dyes RH421 and FITC. Fluorescence changes upon addition of Na+ in the presence of various Mg2+ concentrations were similar and the half-saturation concentrations determined were almost identical. As RH421 responds to binding of Na+ to the n...
Membrane & cell biology, 1998
The goal of work was to investigate the electrogenic transport of Na ions by Na+,K(+)-ATPase in m... more The goal of work was to investigate the electrogenic transport of Na ions by Na+,K(+)-ATPase in membrane fragments absorbed on a planar bilayer lipid membrane. The photorelease of ATP from an inactive precursor, caged ATP, induced a transient current and changes in the net system capacitance measured during the application of an alternating voltage. The increments of capacitance (delta c) decreased with the increase in the frequency of the applied voltage. The characteristic frequency F0 of the steepest slope of the curve significantly decreased in solutions with high ionic strength (either NaCl or choline chloride), in which Na+ transport is decelerated. The value of delta c correlated with the total charge delta q transported across the membrane. The capacitance increments decreased when the Na+ concentration in solution decreased. At a concentration below 2 mM the increment became negative. The increase in membrane capacitance can be attributed to the charge relaxation process in...
Biofizika
The inner field compensation method was used for the measurement of the boundary dipole potential... more The inner field compensation method was used for the measurement of the boundary dipole potentials as a function of phloretin and fluorescein concentration, ionic strength and pH. These potentials were compared with calculated from the conductance change in the presence of nonactin. Both methods gave similar results for fluorescein, but the steady-state potentials in the case of phloretin, obtained by the first method were smaller. These results imply that fluorescein, being introduced on one side of the BLM, remained on that side contrary to phloretin which penetrated through the membrane and partitioned between its both boundaries.
Journal of Biochemical and Biophysical Methods, 1990
ABSTRACT
The Journal of General Physiology, 2003
Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of ... more Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of human eosinophils, at various pHi with pHo 7.5 or 6.5 pipette solutions. H+ current fluctuations were observed consistently when the membrane was depolarized to voltages that activated H+ current. At pHi ≤ 5.5 the variance increased nonmonotonically with depolarization to a maximum near the midpoint of the H+ conductance-voltage relationship, gH-V, and then decreased, supporting the idea that the noise is generated by H+ channel gating. Power spectral analysis indicated Lorentzian and 1/f components, both related to H+ currents. Unitary H+ current amplitude was estimated from stationary or quasi-stationary variance, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{{\sigma}}_{\mathrm{H}}^{\mathrm{2}}\) \end{document}. We analyze \batchmode \documentclass[fleqn,10pt,legalpa...
European Biophysics Journal, 2001
Na,K-ATPase-enriched membrane fragments adsorbed to lipid bilayers were used to study electrogeni... more Na,K-ATPase-enriched membrane fragments adsorbed to lipid bilayers were used to study electrogenic Na + movements induced by enzyme phosphorylation when ATP was photo-released from inactive caged ATP, and simultaneously by externally applied alternating voltages which allowed the measurement of small ATP-induced membrane admittance changes. A detailed analysis of frequency dependence of the capacitance and conductance increments showed that the observed process consists of more than one electrogenic step. The frequency dependence could be described by the sum of two Lorentzian functions and a constant term. The faster process ($2000 s ±1) was assigned to the release of the ®rst extracellular Na + ion. The corner frequency of the slower Lorentzian (about 30 s ±1) coincided with the reciprocal exponential time constant of the falling phase of the transient current, which can be assigned to the conformational transition. Preferentially, the slower process showed a dependence on the ion concentration of choline salts with dierent anions. The eectiveness of the used chaotropic anions to decelerate the kinetics decreased in agreement with the Hofmeister series, I ± >Br ± >Cl ±. This observation matches their eect on the partition between two phosphoenzyme states of the Na,K-AT-Pase, as established previously.
Biophysical Journal, 2000
The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to... more The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to trigger a localized photodynamic reaction; i.e., the amount of carbonyl cyanide m-chlorophenylhydrazone (CCCP) molecules damaged in the leaflet facing the photosensitizer is roughly identical to the total amount of CCCP inactivated. Whereas the latter quantity is assessed from the drop in membrane conductivity G, the former is evaluated from the photopotential that is proportional to the interfacial concentration difference of the uncoupler. Localized photodestruction is encountered by CCCP diffusion to the site of photodamage. A simple model that accounts for both photoinhibition and diffusion predicts the dependence of the photopotential on light intensity, buffer capacity, and pH of the medium. It is concluded that only a limited amount of the reactive oxygen species responsible for CCCP photodamage diffuses across the membrane. If the concentration of reactive oxygen species is decreased by addition of NaN 3 or by substituting aqueous oxygen for argon, is inhibited. If, in contrast, their life time is increased by substitution of H 2 O for D 2 O, increases.
![Research paper thumbnail of Fast Transient Currents in Na,K-ATPase Induced by ATP Concentration Jumps from the P3-[1-(3′,5′-Dimethoxyphenyl)-2-Phenyl-2-Oxo]ethyl Ester of ATP](https://attachments.academia-assets.com/116185817/thumbnails/1.jpg)
](Biophysical Journal, 1998
Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a... more Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a model system of protein-containing membrane fragments adsorbed to planar lipid bilayers. Sodium transport was triggered by ATP concentration jumps in which ATP was released from an inactive precursor by an intense near-UV light flash. The method has been used previously with the P 3-1-(2-nitrophenyl)ethyl ester of ATP (NPE-caged ATP), from which the relatively slow rate of ATP release limits analysis of processes in the pump mechanism controlled by rate constants greater than 100 s Ϫ1 at physiological pH. Here Na,K-ATPase was reinvestigated using the P 3-[1-(3,5-dimethoxyphenyl)-2-phenyl-2-oxo]ethyl ester of ATP (DMB-caged ATP), which has an ATP release rate of Ͼ10 5 s Ϫ1. Under otherwise identical conditions, photorelease of ATP from DMB-caged ATP showed faster kinetics of the transient current compared to that from NPE-caged ATP. With DMB-caged ATP, transient currents had rate profiles that were relatively insensitive to pH and the concentration of caged compound. Rate constants of ATP binding and of the E 1 to E 2 conformational change were compatible with earlier studies. Rate constants of enzyme phosphorylation and ADP-dependent dephosphorylation were 600 s Ϫ1 and 1.5 ϫ 10 6 M Ϫ1 s Ϫ1 , respectively, at pH 7.2 and 22°C.
Biophysical Journal, 2009
The efficiency of photodynamic reactions depends on 1), the penetration depth of the photosensiti... more The efficiency of photodynamic reactions depends on 1), the penetration depth of the photosensitizer into the membrane and 2), the sidedness of the target. Molecules which are susceptible to singlet oxygen (1 O 2) experience less damage when separated from the photosensitizer by the membrane. Since 1 O 2 lifetime in the membrane environment is orders of magnitude longer than the time required for nonexcited oxygen (O 2) to cross the membrane, this observation suggests that differences between the permeabilities or membrane partition of 1 O 2 and O 2 exist. We investigated this hypothesis by releasing 1 O 2 at one side of a planar membrane while monitoring the kinetics of target damage at the opposite side of the same membrane. Damage to the target, represented by dipole-modifying molecules (phloretin or phlorizin), was indicated by changes in the interleaflet dipole potential difference D4 b. A simple analytical model allowed estimation of the 1 O 2 interleaflet concentration difference from the rate at which D4 b changed. It confirmed that the lower limit of 1 O 2 permeability is~2 cm/s; i.e., it roughly matches O 2 permeability as predicted by Overton's rule. Consequently, the membrane cannot act as a barrier to 1 O 2 diffusion. Differences in the reaction rates at the cytoplasmic and extracellular membrane leaflets may be attributed only to 1 O 2 quenchers inside the membrane.
Bioelectrochemistry and Bioenergetics, 1990
A generalized concept of membrane equilibrium is proposed which is based on the assumption that i... more A generalized concept of membrane equilibrium is proposed which is based on the assumption that ion transport across the membrane ceases. The Nernst-Donnan equilibrium does not contradict this concept, but is considered as a particular case where the transport of ions across the membrane ceases when their electrochemical potentials in the aqueous phases are equal. The Nernst-Donnan equilibrium occurs provided the ions penetrate across the membrane independently; in this case both conditions of equilibrium-the cessation of transport and the equality of the ion electrochemical potentials in the solution-are equivalent. In mar.2 complicated types of transport, when flows of several different species are coupled, the transport may cease even though the corresponding electrochemical potentials in the aqueous phases are not equal. In this case membrane equilibrium occurs in the absence of the Donnan equilibrium, and an anomalous potential, which does not obey the Nernst relation, is established across the membrane. If there exists a concentration gradient for one type of ion. the sign of the potential may be opposite to that of the equilibrium potential of the membrane when it is selective for this type of ion. and the absolute value of the potential may be higher thar. the corresponding equilibrium potential. The proposal of anomalous potentials may reveal new aspects of the potential control mechanisms in biological membranes where coupled transport is observed quite frequently.
Bioelectrochemistry and Bioenergetics, 1983
The photoresponses of planar bimolecular lipid membranes (BLM) modified with liposomes containing... more The photoresponses of planar bimolecular lipid membranes (BLM) modified with liposomes containing bacteriorhodopsin (BR) were investigated in the presence of Ca2+ cations. Short-circuit currents during switch-on and switch-off of the light were measured within a time scale exceeding the BR photocycle, and the dependence of the currents on external field and membrane conductance was studied. A comparison of the experimental data with computed values indicates that the photoresponses observed are due not only to BR contained in the proteoliposomes adhered to the BLM, as generally believed, but also to BR in BLM itself. The transfer of BR to BLM may result from the complete fusion of liposomes with the planar membrane. The existence of such a transfer is indicative of the possibility of obtaining the most convenient model system for BR studies: a planar bimolecular lipid membrane containing incorporated BR. LIST OF SYMBOLS A BLM BR CC c, area bimolecular lipid membrane bacteriorhodopsin capacitance of the contact area between the BLM and the adhered liposomes capacitance of the portion of liposome membrane not in contact with BLM eH electric charge of the proton G, conductance of the source equivalent to the BR battery G BR internal conductance of the BR molecule
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
The effects of the adsorption of the fluorescent potential-sensitive dyes RH-421, RH-237 and RH-1... more The effects of the adsorption of the fluorescent potential-sensitive dyes RH-421, RH-237 and RH-160 on the bilayer lipid membrane were studied. It was shown that a dipole potential drop, positive in the hydrophobic part of the membrane, arose due to the dye adsorption. The dye adsorption led to a considerable increase of the rate constant of hydrophobic anion translocation through the membrane, but did not affect their partition coefficient between membrane and water. It implies that the region of the membrane where the potential drops is located deeper than the adsorption plane of hydrophobic ions. The values of the boundary potential differences were estimated by two independent methods with unilateral and bilateral application of the dyes to lipid bilayer membranes. The results suggest that RH dye molecules penetrate through the lipid bilayers. The values of ~'-potential in liposomes did not change on dye adsorption. Hence, dye molecules are adsorbed in a form that does not change the surface charge. We estimated the effects of the electric field of dye dipole layer on an individual dipole located in the same layer and on ion transport through a membrane protein Na'-/K+-ATPase. It turned out that the local electric field of each dye dipole decayed so rapidly that a neighbouring dye molecule did not feel it. It also appeared that RH dyes could have but a minor effect on the electrogenic transport performed by the sodium pump in the examined range of dye concentrations.
Annals of the New York Academy of Sciences, 1997
Biochimica et Biophysica Acta (BBA) - Bioenergetics
Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated io... more Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated ion channels, but differ in containing the conduction pathway. Essential to the functions of HV1 channels in many cells and species is a unique feature called ΔpH dependent gating. The pH on both sides of the membrane strictly regulates the voltage range of channel opening, generally resulting in exclusively outward proton current. Two types of mechanisms could produce ΔpH dependent gating. The "countercharge" mechanism proposes that protons destabilize salt bridges between amino acids in the protein that stabilize specific gating configurations (closed or open). An "electrostatic" mechanism proposes that protons bound to the channel alter the electrical field sensed by the protein. Obligatory proton binding within the membrane electrical field would contribute to measured gating charge. Estimations on the basis of the electrostatic model explain ΔpH dependent gating, but quantitative modeling requires calculations of electric field inside the protein which, in turn, requires knowledge of its structure. We conclude that both mechanisms operate and contribute to ΔpH dependent gating of HV1.
Biochemistry (Moscow) Supplement Series A: Membrane and Cell Biology, 2010
The effect of pH on electrogenic sodium transport by the Na+ ,K+ -ATPase has been studied. Experi... more The effect of pH on electrogenic sodium transport by the Na+ ,K+ -ATPase has been studied. Experiments were carried out by admittance recording in a model system consisting of a bilayer lipid membrane with adsorbed membrane fragments containing purified Na+ ,K+ -ATPase. Changes in the membrane admittance (capacitance and conductance increments in response to photo-induced release of ATP from caged ATP) were measured as function of AC voltage frequency, sodium ion concentration, and pH. In solutions containing 150 m M Na+, the frequency dependence of capacitance increments was not significantly dependent on pH in the range between 6 and 8. At a low NaCl concentration (3 mM), the capacitance increments at low frequencies decreased with the increasing pH. In the absence ofNaCl, the frequency-dependent capacitance increment at low frequencies was similar to that measured in the presence of 3 mM NaCI. These results may be explained by involvement of protons in the Na+, K+ -ATPase pump cycle, i.e., electroneutral exchange of sodium ions for protons under physiological conditions, electrogenic transport of sodium ions at high pH, and electrogenic transport of protons at low concentrations (and in the absence) of sodium ions.
Biologicheskie Membrany, 2007
European Biophysics Journal, 2019
Biophysical Journal, 2020
Acta physiologica Scandinavica. Supplementum, 1998
The complex functions of the Na,K-ATPase can be described by reaction cycles based on the general... more The complex functions of the Na,K-ATPase can be described by reaction cycles based on the generally accepted "Post-Albers cycle". By appropriate experimental conditions various, partly overlapping partial reactions may be isolated which allow the investigation of specific reaction steps and their succession. From kinetic analysis rate constants and dielectric properties may be determined which characterize the function of the ion pump and allow the formulation of constraints with respect to structure-function relations. This is exemplified by two partial reactions which comprise (1) the ATP-driven Na+ transport, and (2) binding of Na+ ions to the cytoplasm sites. Equilibrium Na+ titration experiments were performed using the fluorescent dyes RH421 and FITC. Fluorescence changes upon addition of Na+ in the presence of various Mg2+ concentrations were similar and the half-saturation concentrations determined were almost identical. As RH421 responds to binding of Na+ to the n...
Membrane & cell biology, 1998
The goal of work was to investigate the electrogenic transport of Na ions by Na+,K(+)-ATPase in m... more The goal of work was to investigate the electrogenic transport of Na ions by Na+,K(+)-ATPase in membrane fragments absorbed on a planar bilayer lipid membrane. The photorelease of ATP from an inactive precursor, caged ATP, induced a transient current and changes in the net system capacitance measured during the application of an alternating voltage. The increments of capacitance (delta c) decreased with the increase in the frequency of the applied voltage. The characteristic frequency F0 of the steepest slope of the curve significantly decreased in solutions with high ionic strength (either NaCl or choline chloride), in which Na+ transport is decelerated. The value of delta c correlated with the total charge delta q transported across the membrane. The capacitance increments decreased when the Na+ concentration in solution decreased. At a concentration below 2 mM the increment became negative. The increase in membrane capacitance can be attributed to the charge relaxation process in...
Biofizika
The inner field compensation method was used for the measurement of the boundary dipole potential... more The inner field compensation method was used for the measurement of the boundary dipole potentials as a function of phloretin and fluorescein concentration, ionic strength and pH. These potentials were compared with calculated from the conductance change in the presence of nonactin. Both methods gave similar results for fluorescein, but the steady-state potentials in the case of phloretin, obtained by the first method were smaller. These results imply that fluorescein, being introduced on one side of the BLM, remained on that side contrary to phloretin which penetrated through the membrane and partitioned between its both boundaries.
Journal of Biochemical and Biophysical Methods, 1990
ABSTRACT
The Journal of General Physiology, 2003
Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of ... more Voltage-gated proton channels were studied under voltage clamp in excised, inside-out patches of human eosinophils, at various pHi with pHo 7.5 or 6.5 pipette solutions. H+ current fluctuations were observed consistently when the membrane was depolarized to voltages that activated H+ current. At pHi ≤ 5.5 the variance increased nonmonotonically with depolarization to a maximum near the midpoint of the H+ conductance-voltage relationship, gH-V, and then decreased, supporting the idea that the noise is generated by H+ channel gating. Power spectral analysis indicated Lorentzian and 1/f components, both related to H+ currents. Unitary H+ current amplitude was estimated from stationary or quasi-stationary variance, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{{\sigma}}_{\mathrm{H}}^{\mathrm{2}}\) \end{document}. We analyze \batchmode \documentclass[fleqn,10pt,legalpa...
European Biophysics Journal, 2001
Na,K-ATPase-enriched membrane fragments adsorbed to lipid bilayers were used to study electrogeni... more Na,K-ATPase-enriched membrane fragments adsorbed to lipid bilayers were used to study electrogenic Na + movements induced by enzyme phosphorylation when ATP was photo-released from inactive caged ATP, and simultaneously by externally applied alternating voltages which allowed the measurement of small ATP-induced membrane admittance changes. A detailed analysis of frequency dependence of the capacitance and conductance increments showed that the observed process consists of more than one electrogenic step. The frequency dependence could be described by the sum of two Lorentzian functions and a constant term. The faster process ($2000 s ±1) was assigned to the release of the ®rst extracellular Na + ion. The corner frequency of the slower Lorentzian (about 30 s ±1) coincided with the reciprocal exponential time constant of the falling phase of the transient current, which can be assigned to the conformational transition. Preferentially, the slower process showed a dependence on the ion concentration of choline salts with dierent anions. The eectiveness of the used chaotropic anions to decelerate the kinetics decreased in agreement with the Hofmeister series, I ± >Br ± >Cl ±. This observation matches their eect on the partition between two phosphoenzyme states of the Na,K-AT-Pase, as established previously.
Biophysical Journal, 2000
The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to... more The adsorption of a membrane-impermeable photosensitizer to only one membrane leaflet is found to trigger a localized photodynamic reaction; i.e., the amount of carbonyl cyanide m-chlorophenylhydrazone (CCCP) molecules damaged in the leaflet facing the photosensitizer is roughly identical to the total amount of CCCP inactivated. Whereas the latter quantity is assessed from the drop in membrane conductivity G, the former is evaluated from the photopotential that is proportional to the interfacial concentration difference of the uncoupler. Localized photodestruction is encountered by CCCP diffusion to the site of photodamage. A simple model that accounts for both photoinhibition and diffusion predicts the dependence of the photopotential on light intensity, buffer capacity, and pH of the medium. It is concluded that only a limited amount of the reactive oxygen species responsible for CCCP photodamage diffuses across the membrane. If the concentration of reactive oxygen species is decreased by addition of NaN 3 or by substituting aqueous oxygen for argon, is inhibited. If, in contrast, their life time is increased by substitution of H 2 O for D 2 O, increases.
Biophysical Journal, 1998
Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a... more Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a model system of protein-containing membrane fragments adsorbed to planar lipid bilayers. Sodium transport was triggered by ATP concentration jumps in which ATP was released from an inactive precursor by an intense near-UV light flash. The method has been used previously with the P 3-1-(2-nitrophenyl)ethyl ester of ATP (NPE-caged ATP), from which the relatively slow rate of ATP release limits analysis of processes in the pump mechanism controlled by rate constants greater than 100 s Ϫ1 at physiological pH. Here Na,K-ATPase was reinvestigated using the P 3-[1-(3,5-dimethoxyphenyl)-2-phenyl-2-oxo]ethyl ester of ATP (DMB-caged ATP), which has an ATP release rate of Ͼ10 5 s Ϫ1. Under otherwise identical conditions, photorelease of ATP from DMB-caged ATP showed faster kinetics of the transient current compared to that from NPE-caged ATP. With DMB-caged ATP, transient currents had rate profiles that were relatively insensitive to pH and the concentration of caged compound. Rate constants of ATP binding and of the E 1 to E 2 conformational change were compatible with earlier studies. Rate constants of enzyme phosphorylation and ADP-dependent dephosphorylation were 600 s Ϫ1 and 1.5 ϫ 10 6 M Ϫ1 s Ϫ1 , respectively, at pH 7.2 and 22°C.
Biophysical Journal, 2009
The efficiency of photodynamic reactions depends on 1), the penetration depth of the photosensiti... more The efficiency of photodynamic reactions depends on 1), the penetration depth of the photosensitizer into the membrane and 2), the sidedness of the target. Molecules which are susceptible to singlet oxygen (1 O 2) experience less damage when separated from the photosensitizer by the membrane. Since 1 O 2 lifetime in the membrane environment is orders of magnitude longer than the time required for nonexcited oxygen (O 2) to cross the membrane, this observation suggests that differences between the permeabilities or membrane partition of 1 O 2 and O 2 exist. We investigated this hypothesis by releasing 1 O 2 at one side of a planar membrane while monitoring the kinetics of target damage at the opposite side of the same membrane. Damage to the target, represented by dipole-modifying molecules (phloretin or phlorizin), was indicated by changes in the interleaflet dipole potential difference D4 b. A simple analytical model allowed estimation of the 1 O 2 interleaflet concentration difference from the rate at which D4 b changed. It confirmed that the lower limit of 1 O 2 permeability is~2 cm/s; i.e., it roughly matches O 2 permeability as predicted by Overton's rule. Consequently, the membrane cannot act as a barrier to 1 O 2 diffusion. Differences in the reaction rates at the cytoplasmic and extracellular membrane leaflets may be attributed only to 1 O 2 quenchers inside the membrane.
Bioelectrochemistry and Bioenergetics, 1990
A generalized concept of membrane equilibrium is proposed which is based on the assumption that i... more A generalized concept of membrane equilibrium is proposed which is based on the assumption that ion transport across the membrane ceases. The Nernst-Donnan equilibrium does not contradict this concept, but is considered as a particular case where the transport of ions across the membrane ceases when their electrochemical potentials in the aqueous phases are equal. The Nernst-Donnan equilibrium occurs provided the ions penetrate across the membrane independently; in this case both conditions of equilibrium-the cessation of transport and the equality of the ion electrochemical potentials in the solution-are equivalent. In mar.2 complicated types of transport, when flows of several different species are coupled, the transport may cease even though the corresponding electrochemical potentials in the aqueous phases are not equal. In this case membrane equilibrium occurs in the absence of the Donnan equilibrium, and an anomalous potential, which does not obey the Nernst relation, is established across the membrane. If there exists a concentration gradient for one type of ion. the sign of the potential may be opposite to that of the equilibrium potential of the membrane when it is selective for this type of ion. and the absolute value of the potential may be higher thar. the corresponding equilibrium potential. The proposal of anomalous potentials may reveal new aspects of the potential control mechanisms in biological membranes where coupled transport is observed quite frequently.
Bioelectrochemistry and Bioenergetics, 1983
The photoresponses of planar bimolecular lipid membranes (BLM) modified with liposomes containing... more The photoresponses of planar bimolecular lipid membranes (BLM) modified with liposomes containing bacteriorhodopsin (BR) were investigated in the presence of Ca2+ cations. Short-circuit currents during switch-on and switch-off of the light were measured within a time scale exceeding the BR photocycle, and the dependence of the currents on external field and membrane conductance was studied. A comparison of the experimental data with computed values indicates that the photoresponses observed are due not only to BR contained in the proteoliposomes adhered to the BLM, as generally believed, but also to BR in BLM itself. The transfer of BR to BLM may result from the complete fusion of liposomes with the planar membrane. The existence of such a transfer is indicative of the possibility of obtaining the most convenient model system for BR studies: a planar bimolecular lipid membrane containing incorporated BR. LIST OF SYMBOLS A BLM BR CC c, area bimolecular lipid membrane bacteriorhodopsin capacitance of the contact area between the BLM and the adhered liposomes capacitance of the portion of liposome membrane not in contact with BLM eH electric charge of the proton G, conductance of the source equivalent to the BR battery G BR internal conductance of the BR molecule
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
The effects of the adsorption of the fluorescent potential-sensitive dyes RH-421, RH-237 and RH-1... more The effects of the adsorption of the fluorescent potential-sensitive dyes RH-421, RH-237 and RH-160 on the bilayer lipid membrane were studied. It was shown that a dipole potential drop, positive in the hydrophobic part of the membrane, arose due to the dye adsorption. The dye adsorption led to a considerable increase of the rate constant of hydrophobic anion translocation through the membrane, but did not affect their partition coefficient between membrane and water. It implies that the region of the membrane where the potential drops is located deeper than the adsorption plane of hydrophobic ions. The values of the boundary potential differences were estimated by two independent methods with unilateral and bilateral application of the dyes to lipid bilayer membranes. The results suggest that RH dye molecules penetrate through the lipid bilayers. The values of ~'-potential in liposomes did not change on dye adsorption. Hence, dye molecules are adsorbed in a form that does not change the surface charge. We estimated the effects of the electric field of dye dipole layer on an individual dipole located in the same layer and on ion transport through a membrane protein Na'-/K+-ATPase. It turned out that the local electric field of each dye dipole decayed so rapidly that a neighbouring dye molecule did not feel it. It also appeared that RH dyes could have but a minor effect on the electrogenic transport performed by the sodium pump in the examined range of dye concentrations.
Annals of the New York Academy of Sciences, 1997
Biochimica et Biophysica Acta (BBA) - Bioenergetics
Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated io... more Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated ion channels, but differ in containing the conduction pathway. Essential to the functions of HV1 channels in many cells and species is a unique feature called ΔpH dependent gating. The pH on both sides of the membrane strictly regulates the voltage range of channel opening, generally resulting in exclusively outward proton current. Two types of mechanisms could produce ΔpH dependent gating. The "countercharge" mechanism proposes that protons destabilize salt bridges between amino acids in the protein that stabilize specific gating configurations (closed or open). An "electrostatic" mechanism proposes that protons bound to the channel alter the electrical field sensed by the protein. Obligatory proton binding within the membrane electrical field would contribute to measured gating charge. Estimations on the basis of the electrostatic model explain ΔpH dependent gating, but quantitative modeling requires calculations of electric field inside the protein which, in turn, requires knowledge of its structure. We conclude that both mechanisms operate and contribute to ΔpH dependent gating of HV1.