Correlation of photochemical cycle, H<sup>+</sup> release and uptake, and electric events in bacteriorhodopsin

Drachev, Lel A.; Kaulen, Andrey D.; Skulachev, V. P.

doi:10.1016/0014-5793(84)80628-6

Cited by 138 publications

(111 citation statements)

References 18 publications

Supporting

Mentioning

103

Contrasting

Order By: Relevance

“…In the extravesicular space, at early times (Fig. 3), proton concentration changes are detected resulting from the release of protons by BR during (or even before) the formation of the M intermediate (5,6). These protons are released by the outward pumping fraction ofproteins (outside out).…”

Section: Resultsmentioning

confidence: 98%

“…However, the molecular mechanism by which, during the complex photochemical cycle, one proton per BR molecule (2)(3)(4)(5)(6) is vectorially translocated across the membrane is far from understood. Interpretation of measured functional data is hampered by the extraordinary organization of the photopigment in the cytoplasmic membrane of the cell.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Grzesiek

Dencher

1988

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

View full text Add to dashboard Cite

The question of the basic functional transport unit of bacteriorhodopsin (BR) has been addressed by comparing the proton pumping stoichiometry as well as the photocycle kinetics of monomeric and aggregated BR in phospholipid vesicles. When time-resolved laser spectroscopy was used in combination with the optical pH-indicator pyranine, single-turnover experiments revealed approximately 0.5-0.8 and 0.8-1.2 protons vectorially translocated per photocycling monomeric and aggregated BR molecule, respectively. Since both these values are akin and very similar to the pumping stoichiometry of crystalline BR molecules in the purple membrane, the BR monomer has been proven to be the essential transport unit. The natural arrangement of the photopigments in a crystalline array of immobilized trimers is not required for efficient vectorial proton translocation.The light-energy-converting membrane protein bacteriorhodopsin (BR), which has a covalently bound retinal as chromophore (1), has gained special attention due to its relative simplicity. However, the molecular mechanism by which, during the complex photochemical cycle, one proton per BR molecule (2-6) is vectorially translocated across the membrane is far from understood. Interpretation of measured functional data is hampered by the extraordinary organization of the photopigment in the cytoplasmic membrane of the cell. As the only protein of the so-called purple membrane (PM), it is arranged in a two-dimensional hexagonal lattice of protein trimers (7,8) which are separated from neighboring trimer clusters by only one shell of lipids (9). To interpret various experimental results with the aim of constructing a working model for BR's proton-transport mechanism, the basic functional unit of this light-driven proton pump has to be defined; the functional unit could be the monomer, the trimer, or even the lattice.BR monomers do exhibit vectorial H+-transport activity (10-13). However, the important question whether or not monomeric BR has the same efficiency as the aggregate is controversial (12)(13)(14) To accelerate the relaxation of a pH gradient and a membrane potential generated after a single flash or after light adaptation, the vesicles were incubated with 1 ,M of the ion channel gramicidin above the phase transition temperature of the lipids for 10 min and thereafter sonicated for 20 s to improve the incorporation. The sample was then divided into two 1-ml aliquots, one was incubated additionally with 50 ,M pyranine in the extravesicular medium, and both were degassed at 0.1 torr (13 Pa) for 3 min. After pH adjustment (pH 7.0) at the temperature of the flash-spectroscopic experiments, the measurements were carried out at once. The buffer capacity of the samples containing pyranine was determined by titration with KOH and HCl in the range of pH 6.7-7.3. Flash Spectroscopy. The flash spectrometer (excitation wavelength Aex = 580 ± 20 nm; 1 mJ; flash duration 5-10 ns) equipped with a logarithmic time base has been described elsewhere (6). Before the flash and ...

show abstract

Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Grzesiek

Dencher

1988

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

View full text Add to dashboard Cite

show abstract

“…However, the 'electrical' distance ratios may differ significantly from the spatial ones due to variation in the intraprotein dielectric constant along the charge transfer traectory, as has been demonstrated for instance for bacteriorhodopsin (cf. [36,37]) or R. viridis reaction centres [18]. According to the classical work of Hinkle and Mitchell [33], heme a is localized electrically in the middle of the COX dielectric barrier, so we assume 1 = 0.5 in Eq.…”

Section: Quantitation Of the Electric Responsementioning

confidence: 99%

Flash‐induced membrane potential generation by cytochrome c oxidase

et al. 1993

View full text Add to dashboard Cite

Flash‐induced single‐electron reduction of cytochrome c oxidase. Compound F (oxoferryl state) by RuII(2,2'‐bipyridyl)2+ 3 [Nilsson (1992) Proc. Natl. Acad. Sci. USA 89, 6497‐6501] gives rise to three phases of membrane potential generation in proteoliposomes with τ values and contributions of ca. 45 μs (20%), 1 ms (20%) and 5 ms (60%). The rapid phase is not sensitive to the binuclear centre ligands, such as cyanide or peroxide, and is assigned to vectorial electron transfer from CuA to heme a. The two slow phases kinetically match reoxidation of heme a, require added H2O2 or methyl peroxide for full development, and are completely inhibited by cyanide; evidently, they are associated with the reduction of Compound F to the Ox state by heme a. The charge transfer steps associated with the F to Ox conversion are likely to comprise (i) electrogenic uptake of a ‘chemical’ proton from the N phase required for protonation of the reduced oxygen atom and (ii) electrogenic H+ pumping across the membrane linked to the F to Ox transition. Assuming heme a ‘electrical location’ in the middle of the dielectric barrier, the ratio of the rapid to slow electrogenic phase amplitudes indicates that the F to Ox transition is linked to transmembrane translocation of 1.5 charges (protons) in addition to an electrogenic uptake of one ‘chemical’ proton required to form Fe3+‐OH− from Fe4+ = O2−. The shortfall in the number of pumped protons and the biphasic kinetics of the millisecond part of the electric response matching biphasic reoxidation of heme a may indicate the presence of 2 forms of Compound F, reduction of only one of which being linked to full proton pumping.

show abstract

“…This perpetual, release and binding sequence is the major cause of proton delay on the surface. The discharge of proton to the bulk is controlled by the density of the protonable sites on the surface and the concentration of the diffusing proton binding molecules (pyranine or buffer) [16,17]. This mechanism has been experimentally and theoretically investigated by Gutman, Nachliel and co-workers [12,18 20].…”

Section: Introductionmentioning

confidence: 99%

Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk

Nachliel

Gutman

1996

FEBS Letters

View full text Add to dashboard Cite

It has been reported by many research groups that protons released during the photocycle of bacteriorhodopsin are detected by surface bound indicators much faster than by indicators in the bulk. In this study we used numerical simulation of chemical reaction's dynamics for analyzing the delayed appearance of protons in the bulk. The results indicate that the low pK surface groups of the membrane, which form an undilutable concentrated matrix of proton binding sites, retain the protons in this space according to the mass action law. The main sites for proton accumulation are the cluster of carboxylates on the cytoplasmic side of the membrane. The protonation of an indicator in the bulk does not proceed by its reaction with free proton, but rather through self-diffusion of the indicator to the membrane and abstraction of proton from the protonated surface group. The detailed mechanisms which correspond with these reactions are reported.

show abstract

Correlation of photochemical cycle, H⁺ release and uptake, and electric events in bacteriorhodopsin

Cited by 138 publications

References 18 publications

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Flash‐induced membrane potential generation by cytochrome c oxidase

Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk

Contact Info

Product

Resources

About

Correlation of photochemical cycle, H+ release and uptake, and electric events in bacteriorhodopsin

Cited by 138 publications

References 18 publications

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

Flash‐induced membrane potential generation by cytochrome c oxidase

Quantitative evaluation of the dynamics of proton transfer from photoactivated bacteriorhodopsin to the bulk

Contact Info

Product

Resources

About

Correlation of photochemical cycle, H⁺ release and uptake, and electric events in bacteriorhodopsin