Energy Transduction by Electroconformational Coupling

Astumian, R. Dean; Chock, P. Boon; Westerhoff, Hans V.; Tsong, Tian Yow

doi:10.1007/978-1-4612-3744-0_30

Cited by 3 publications

(8 citation statements)

References 13 publications

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“…In Fig. 3 this was the transmembrane concentration gradient of P. In accord with the previously mentioned optimal oscillation frequency with respect to transport or synthesis rate (1,2), an optimal fluctuation lifetime was also demonstrated in the case of random electric pulses (9,13,14,19). To enable an enzyme to absorb and transduce free energy from a fluctuating electric field, it is sufficient (for other possibilities, see ref.…”

Section: Discussionsupporting

confidence: 65%

“…The above driving forces contain the terms 4Rfln(o) = 2FAq. This implies that there must be a free energy source worth at least 2FAqi (14).…”

Section: Discussionmentioning

confidence: 99%

“…In the case of autonomous noise, the diagonal terms Another possibility that we have investigated quantitatively is the case in which the fluctuations in the position of the generator charge were driven by the translocation of a substance, P, from the right-hand to the left-hand compartment (13,14,19). Fig.…”

Section: Randomly Fluctuating Electric Fields Canmentioning

confidence: 99%

“…5), and, certainly, large potential fluctuations must occur in the vicinity of ion channels upon opening or closing. This has been used (1,6) as the basis for a model ofATP synthesis via the FO/Fl-ATPase, in which coupling factor Fo serves as a field-modulating channel, the opening and closing of which is linked to the binding and release of ligands in F1. Also, it was suggested that the electric field around HW-transporting ATPase in free energytransducing membranes might oscillate because of turnover of neighboring electron-transfer chains, and that these oscillations might contain the free energy often missing in free energy balances (2).…”

mentioning

confidence: 99%

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Can free energy be transduced from electric noise?

Astumian¹,

Chock²,

Tsong³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

120

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Recently, it was shown that free energy can be transduced from a regularly oscillating electric field to do chemical or transport work when coupled through an enzyme with appropriate electrical characteristics. Here we report that randomly pulsed electric fields can also lead to work being done, giving rise to speculation as to whether appropriately designed enzymes can extract and convert free energy from the inherent fluctuations in their environment. The paradox is resolved by showing that equilibrium electrical noise resulting from the environment around an enzyme cannot be completely random but is correlated to the state that the enzyme is in. If the noise has the appropriate reciprocal interaction with the enzyme, its potential to serve as a free-energy source disappears. This is shown by Monte Carlo and other numerical calculations and is proven analytically by use of the diagram method. This method also is used to provide an explicit equation showing that, under a range of conditions, our model enzyme will be induced by uncorrelated ("autonomous") noise to undergo net cyclic flux. That work can be transduced from the "random" noise is demonstrated by using numerical methods.Recently, it was demonstrated (1, 2) that an oscillating electric field is competent to do chemical work when coupled through an enzyme with differences in macroscopic polarization and basic free energy between its conformational states. These results might well account for the observation that the Na+/K+-ATPase mediates active transport when subjected to an oscillating electric field (1, 3, 4).In vivo, fluctuating electric fields have been observed around cells (reviewed in ref. 5), and, certainly, large potential fluctuations must occur in the vicinity of ion channels upon opening or closing. This has been used (1, 6) as the basis for a model ofATP synthesis via the FO/Fl-ATPase, in which coupling factor Fo serves as a field-modulating channel, the opening and closing of which is linked to the binding and release of ligands in F1. Also, it was suggested that the electric field around HW-transporting ATPase in free energytransducing membranes might oscillate because of turnover of neighboring electron-transfer chains, and that these oscillations might contain the free energy often missing in free energy balances (2).In preliminary calculations, we found that totally random noise, when applied to the system described previously (1, 2), led to work being done. This result suggests that many (indeed most) forms offield fluctuations can do work. Yet we must realize that, in keeping with the laws of thermodynamics, internal noise arising in a system at equilibrium certainly cannot do work.Although the effects of field fluctuations have been studied before for both noncyclic (7) and cyclic (8) systems, our results demonstrate that energy can be transduced from a randomly fluctuating field, allowing an enzyme to do work.In a subsequent paper (9), the general asymmetry requirements for a four-state enzyme to work will be studied i...

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Section: Discussionsupporting

confidence: 65%

“…The above driving forces contain the terms 4Rfln(o) = 2FAq. This implies that there must be a free energy source worth at least 2FAqi (14).…”

Section: Discussionmentioning

confidence: 99%

Section: Randomly Fluctuating Electric Fields Canmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Can free energy be transduced from electric noise?

Astumian¹,

Chock²,

Tsong³

et al. 1987

Proc. Natl. Acad. Sci. U.S.A.

120

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“…Recent work has focused, however, on the possibility of an energy source other than a thermal gradient to power a microscopic motor. If energy is supplied by external fluctuations (5)(6)(7)(8) or a nonequilibrium chemical reaction (9,10), Brownian motion can be biased if the medium is anisotropic, even in an isothermal system. Thus, directed motion is possible without gravitational force, macroscopic electric fields, or long-range spatial gradients of chemicals.…”

Section: R Dean Astumianmentioning

confidence: 99%

Thermodynamics and Kinetics of a Brownian Motor

Astumian

1997

Science

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1,337

1,004

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Nonequilibrium fluctuations, whether generated externally or by a chemical reaction far from equilibrium, can bias the Brownian motion of a particle in an anisotropic medium without thermal gradients, a net force such as gravity, or a macroscopic electric field. Fluctuation-driven transport is one mechanism by which chemical energy can directly drive the motion of particles and macromolecules and may find application in a wide variety of fields, including particle separation and the design of molecular motors and pumps.

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Coupling of vectorial proton flow to a biochemical reaction by local electric interactions.

Kamp

Astumian

Westerhoff

1988

Proc. Natl. Acad. Sci. U.S.A.

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For a transmembrane redox enzyme and a (passive) protonophore, the complete set of rate equations is given. Turnover causes cyclic variation of their electric polarization. This is responsible not only for effects of the electric field on the rate constants but also for the generation of an electric field felt by neighboring molecules. It is calculated that, when the systems are close together at a fixed distance, cycling of the two systems becomes coupled enabling the protonophore to pump protons against their electrochemical gradient. If the electrochemical gradient for protons approaches the input force of the redox reaction, slip (incomplete coupling between the chemical and proton-transport reactions) results. By using different sets of parameters, both kinetically reversible and kinetically irreversible proton pumps can be simulated.Although the involvement of protons in several bioenergetic processes (see ref. 1) is widely acknowledged, the molecular mechanism as well as the stoichiometry (2-4) of proton pumping by membrane-bound proteins remains uncertain. Two lines of thought concerning the mechanism of coupling between vectorial proton flow and biochemical reactions may be distinguished. The first hypothesizes that covalent integration of the pathways of the chemical and pumping reactions is catalyzed by the membrane-bound enzyme (5). The second hypothesizes that the biochemical reaction and vectorial pumping activities take place at different sites on the membrane-embedded enzyme, the free-energy transfer being mediated by the enzyme (6-10).More obviously than the former, the latter mechanism allows for "slip"-i.e., incomplete coupling between the chemical and proton-transport reactions (2)-and, therefore, for proton stoichiometries depending on the balance between the applied thermodynamic forces (for review, see ref. 1). Slip has been experimentally demonstrated in various cases, including the proton pumps involved in oxidative phosphorylation (2-4), the Ca2+-ATPase (11), bacteriorhodopsin (12), and DNA gyrase (13). Fig. 1A shows a kinetic diagram of a proton pump that may display slip. One site (on the translocator part of the pump) may bind or release a proton at either side of the membrane and can go, either without or with a bound proton, from one side of the membrane to the other. Another site (on the enzyme part) can bind a substrate (e.g., NADH, cytochrome c, or ATP), convert it, and release product. Coupling is ensured if the slip transition (Fig. LA) is improbable (1, 14). Although schemes of this sort have been widely applied to studies of slip-related phenomena (e.g., refs. 1, 14-16), they do not explain explicitly what the molecular basis for the restriction on the slip transition 1s.In this paper we present a different type of model for a proton pump. We considered two parts (e.g., subunits) of an enzyme complex, one capable of transporting protons across a membrane (the translocator), the other catalyzing a biochemical reaction (the enzyme) (see Fig. 1B). We will show that if t...

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Energy Transduction by Electroconformational Coupling

Cited by 3 publications

References 13 publications

Can free energy be transduced from electric noise?

Can free energy be transduced from electric noise?

Thermodynamics and Kinetics of a Brownian Motor

Coupling of vectorial proton flow to a biochemical reaction by local electric interactions.

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