Characterization of sodium and proton flows in sub-bacterial particles of Halobacterium halobium in terms of nonequilibrium thermodynamics

Cooper, Shulamit; Michaeli, I.; Caplan, S. Roy

doi:10.1016/0005-2736(83)90165-7

Cited by 4 publications

(1 citation statement)

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“…5 and 7 of Lanyi et al, 1979). In this and calculations given below, a membrane potential or protonmotive force of about -120 mV will be assumed for illuminated cell envelope vesicles if no measured value is reported LK (2 X 10-6 mol Cooper et al (1983) have reported measurements of LHu and…”

Section: Estimates Of the Phenomenological Coupling Coefficientsmentioning

confidence: 99%

Coupling between the bacteriorhodopsin photocycle and the protonmotive force in Halobacterium halobium cell envelope vesicles. III. Time-resolved increase in the transmembrane electric potential and modeling of the associated ion fluxes

Helgerson¹,

Mathew²,

Bivin³

et al. 1985

Biophysical Journal

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Bacteriorhodopsin functions as an electrogenic, light-driven proton pump in Halobacterium halobium. In cell envelope vesicles, its photocycle kinetics can be correlated with membrane potential. The initial decay rate of the M photocycle intermediate(s) decreases with increasing membrane potential, allowing the construction of a calibration curve. The laser (592.5 nm) was flashed at various time delays following the start of background illumination (592 +/- 25 nm) and transient absorbance changes at 418 nm monitored in cell envelope vesicles. The vesicles were loaded with and suspended in either 3 M NaCl or 3 M KCl buffered with 50 mM HEPES at pH 7.5 and the membrane permeability to protons modified by pretreatment with N,N'-dicyclohexylcarbodiimide. In each case the membrane potential rose with a halftime of approximately 75 ms. The steady-state potential achieved depends on the cation present and the proton permeability of the membrane, i.e., higher potentials are developed in dicyclohexylcarbodiimide treated vesicles or in NaCl media as compared with KCl media. The results are modeled using an irreversible thermodynamics formulation, which assumes a constant driving reaction affinity (Ach) and a variable reaction rate (Jr) for the proton-pumping cycle of bacteriorhodopsin. Additionally, the model includes a voltage-gated, electrogenic Na+/H+ antiporter that is active when vesicles are suspended in NaCl. Estimates for the linear phenomenological coefficients describing the overall proton-pumping cycle (Lr = 3.5 X 10(-11)/mol2/J X g X s), passive cation permeabilities (LHu = 2 X 10(-10), LKu = 2.2 X 10(-10), LNau = 1 X 10(-11)), and the Na+/H+ exchange via the antiporter (Lex = 5 X 10(-11)) have been obtained.

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Section: Estimates Of the Phenomenological Coupling Coefficientsmentioning

confidence: 99%