Mechanism of generation and regulation of photopotential by bacteriorhodopsin in bimolecular lipid membrane. The quenching effect of blue light

Ormos, Pál; Dancsházy, Zsolt; Karvaly, Béla

doi:10.1016/0005-2728(78)90190-1

Cited by 48 publications

(38 citation statements)

References 28 publications

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“…The intensity of this light is similar to ambient daylight. The highest intensity was only 2^5 times higher than that was measured in a sunny day in our country [7]. BR is one of the best candidates as a biological material for data storage [4].…”

Section: Discussionmentioning

confidence: 56%

Bleaching of bacteriorhodopsin by continuous light

1999

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A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50^60³C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation-like process. These facts may question the generally held belief that BR is a stable protein in vivo for a long period of time. Our results may have relevance also to practical applications of bacteriorhodopsin where the stability of bacteriorhodopsin is a key issue. In certain instances, the use of bacteriorhodopsin may require cooled conditions. Here, we defined the conditions under which bacteriorhodopsin is stable. The permanent photobleaching offers a new way of picture imaging and information input for bacteriorhodopsinbased optical devices.z 1999 Federation of European Biochemical Societies.

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Section: Discussionmentioning

confidence: 56%

Bleaching of bacteriorhodopsin by continuous light

1999

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“…For both molecules, side-specific protonation reactions have been demonstrated. In halorhodopsin, azide mediates proton equilibration between medium and Schiff base through the cytoplasmic channel (8) and photon absorption by the M state in bacteriorhodopsin leads to proton uptake specifically through the extracellular channel (19). This prompted our reinvestigation of halorhodopsin's ion transport properties in white light.…”

mentioning

confidence: 99%

Light-driven proton or chloride pumping by halorhodopsin.

Bamberg

Tittor

Oesterhelt

1993

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

119

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Halorhodopsin from Halobaceriwn halobium was purified and reconstituted with lipids from purple membranes. The resulting protein-containing membrane sheets were adsorbed to a planar lipid membrane and photoelectric properties were analyzed. Depending on light conditions, halorhodopsin acted either as a light-driven chloride pump or as a proton pump: green light caused chloride transport and additional blue light induced proton pumping. In the living cell, both of these vectorial processes would be directed toward the cytoplasm and, compared to ion transport by bacteriorhodopsin, this is an inversed proton flow. Azide, a catalyst for reversible deprotonation of halorhodopsin, enhanced proton transport, and the deprotonated Schiff base in the 13-cis configuration (11410) was identified as the key intermediate of this alternative catalytic cycle in halorhodopsin. While chloride transport in halorhodopsin is mediated by a one-photon process, proton transport requires the absorption of two photons: one photon for formation of H410 and release of a proton, and one photon for photoisomerization of H410 and re-formation of H578 with concomitant uptake of a proton by the Schiff base.The retinal protein halorhodopsin occurs in the cell membrane of Halobacterium halobium in addition to the proton pump bacteriorhodopsin (for review, see ref. 1). Its function was identified as that ofan inwardly directed Cl-pump (2, 3). After photoisomerization of all-trans-retinal to the 13-cis isomer, halorhodopsin passes a series of distinct intermediates characterized by their respective absorption maxima before returning to the initial state within =14 ms (4). No reversible deprotonation of the Schiff base is connected with the Cl-transport cycle. However, halorhodopsin can produce in a side reaction a species called H410. This product is produced from the photocycle intermediate H520 and contains a deprotonated Schiff base in the 13-cis configuration (5) (see Fig. 7). From the H410 state halorhodopsin returns in a thermal reaction in the time range of seconds to the initial state. Thus, continuous green light inhibits Cl-pumping under concomitant accumulation of H410 (6). Photochemically, the H410 state after isomerization returns much faster to the initial state, and this phenomenon causes the observed blue light regulation of halorhodopsin activity. Thus, irradiance with white light (blue and green light) resulted in an optimal Cl--dependent stationary photocurrent in black lipid membrane experiments (6).Azide accelerates accumulation of H410 drastically, and this was seen as an accelerated inhibition of Cl-transport in green light and a fast reactivation by additional blue light. The effect ofazide is catalysis of the deprotonation reaction of the Schiff base (7,8). Recent elucidation of the proton transport mechanism in bacteriorhodopsin by structural, genetic, biochemical, and biophysical studies (9, 10) helped considerably in understanding the analogue molecular processes in halorhodopsin. Halorhodopsin lacks the aspartic...

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“…This is explained as follows: Since the Schiff-base of BR is deprotonated in BRQ12 state, proton translocation occurs in the pumping direction during the formation of BRw, observed as the fast rise (7-50 ps) in the photopotential [3]. It was proposed [2] that blue light excitation of Bb12 either prevents proton release from the membrane, or causes proton rebinding from the side of the membrane to which it has been released. In both cases proton translocation to the Schiff-base, against the pumping direction (from either the intramolecular or the extramolecular space) takes place, which causes this fast fall in photopotential.…”

Section: Resultsmentioning

confidence: 99%

“…In control measurements on the steady-state behaviour of two model systems: BR in bimolecular lipid membrane [2] and BR in lipid-impregnated collodion membrane (BR-CLM) [3] it turned out that as far as the effects under investigation are concerned both of them demonstrate qualitatively the I;EBS LETTERS December 1978 same responses. The BR-CLM was chosen for the present work since it demonstrated higher stability and larger photopotential values.…”

Section: Methodsmentioning

confidence: 99%