Branching in the Bacteriorhodopsin Photochemical Cycle

Sherman, Warren V.; Eicke, Robert R.; Stafford, Shirley R.; Wasacz, F. M.

doi:10.1111/j.1751-1097.1979.tb07204.x

Cited by 32 publications

(19 citation statements)

References 15 publications

(7 reference statements)

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“…The effect of temperature on the photocycle has been studied by several investigators (20)(21)(22). Racker and Hinkle (23) studies showed that increasing temperature decreased the efficiency of proton uptake by reconstituted phospholipid vesicles containing bR, a result qualitatively similar to that reported here.…”

Section: Discussionsupporting

confidence: 78%

A correlation between proton pumping and the bacteriorhodopsin photocycle.

Li¹,

Govindjee²,

Ebrey³

1984

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

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In an attempt to establish a relationship between proton pumping and the photocycle intermediates of bacteriorhodopsin, we have studied the effects of pH and tem. perature on flash-induced proton pumping and the photointermediates 0640 and M412. The relative quantum yield of flashinduced proton pumping is both pH and temperature dependent. It is high in the acid pH range and at low temperatures but decreases in the basic pH range and at high temperatures. The decay of M412 is biphasic. The amplitude of the slowly decaying component (MS) was found to be pH dependent with a pK similar to that of the ApH. The pH dependence of the fast-decaying component (Mf) is opposite to that of Ms and ApH. Like that of MS, the amplitude of 060 is high in the acid pH range, but unlike the amplitude of MS, it declines very rapidly at pHs greater than 6.5; the amplitude of 060 becomes zero around pH 8. The temperature dependence of the amplitude of Ms was found to be similar to that of ApH, being high at low temperatures and low in the high-temperature range.The temperature dependence of Mf and 060 is opposite to that of ApH and MS. Whereas, 06o and Ms seem to be likely candidates (from the pH dependence) for coupling between proton pumping and the photocycle, M" is more likely because ('l the relative quantum yield of both Ms and ApH seem not to go to zero at higher pHs and (it) M! and ApH have similar temperature dependence.Bacteriorhodopsin (bR) is the only protein in the purple membrane of Halobacterium halobium. The color of bR is due to its chromophore, retinal, which is attached to the apoprotein via a protonated Schiff base linkage. Light initiates a photocycle consisting of a series of transient metastable intermediates usually identified by an appropriate absorption maximum-K630, L550, M410, 06O, etc. The cycle is completed with the reformation of the original pigment, bR570. During the photocycle, protons are released at the external surface of the purple membrane and taken up at its cytoplasmic side (see general reviews in refs. 1 and 2). Resonance Raman studies (3,4) show that when the intermediate M412 is formed, the Schiff base becomes deprotonated, suggesting both that protons which are pumped across the cell membrane may be from the pigment's protonated Schiff base and that intermediate M412 should couple with proton translocation. However, the first suggestion is belied by quantitative measurements showing that, under some experimental conditions, more than one proton can be pumped out per deprotonated Schiff base intermediate formed (5-8).As regards the second suggestion, several studies have examined the correlation between proton movements and the photocycle and have given different answers. A complicating feature of the coupling question is that proton release and uptake both are single exponential processes, but M412 rise and decay are the sum of at least two exponential processes, Mslow (MS) and Mfast (Me) (6,(9)(10)(11). To study the correlation of the kinetics of proton movement with the kinetics o...

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Section: Discussionsupporting

confidence: 78%

A correlation between proton pumping and the bacteriorhodopsin photocycle.

Li¹,

Govindjee²,

Ebrey³

1984

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

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“…At 45°C the maximum concentration of 0 -B R is more than 3 times higher than at 14°C (Gillbro, 1978). The reason for this temperature effect is probably that the rate of 0 -B R formation is much slower than its decay rate at lower temperatures (Gillbro, 1978) or alternatively that there is a temperature-sensitive branching of the photocycle between M-BR and 0 -B R (Sherman et a/., 1979). We did not notice any change in the ps signal of Figure 1 as the temperature of the sample was varied between 0 and 30°C.…”

Section: Identification Of the Photoproductmentioning

confidence: 75%

PICOSECOND KINETICS and A MODEL FOR THE PRIMARY EVENTS OF BACTERIORHODOPSIN

Gillbro

Sundström

1983

Photochem & Photobiology

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The picosecond absorption kinetics of light adapted bacteriorhodops in (BR) are reported for water and glycerol‐water suspensions of purple membrane from Halobacieriwn hulobium at different temperatures (77‐300 K) and pH (5‐10). It is shown that a photoproduct of BR, called P‐BR (pseudo‐bacteriorhodopsin). is responsible for the 16 ± 2 ps relaxation lifetime observed under steady state irradiation (i.e. with a train of ps pulses) at room temperature. At 77 K the absorption recovery lifetime is 62 ± 5 ps in good agreement with previous fluorescence lifetime studies. The observed signal is very sensitive to the sample flow rate and at the highest flow rates a fast absorbance increase (≤ 2 ps) is observed at λ > 620 nm. while at 576 nm a similarly fast absorption recovery alter bleaching is observed. These results imply that the reaction BR → K‐BR occurs within 2 ps. In order to explain the simultaneous formation of P‐BR and K‐BR at 77 K. a model for the primary events including a traus‐cis isomerization and a protein relaxation about the chromophore is suggested. The same model can also be used in explaining the simultaneous formation of batho‐ and hypsorhodopsin in some rhodopsins. Finally, a scheme for the last steps in the photocycle of bacteriorhodopsin including protonation, protein relaxation and cis‐trans isomerization is proposed

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“…1 a). This assumption is based on the observation that the ratio between apparent time constants of formation and decay of the O0 intermediate is practically temperature independent (7); hence, the temperature dependence of the O0 maximum reflects the dependence of the transient concentration of the O0 intermediate, which is illustrated in the transmittance record of Fig. 1 tional T-jump pulses at two diffc photocycle.…”

Section: Resultsmentioning

confidence: 99%

Temperature and pH sensitivity of the O640 intermediate of the bacteriorhodopsin photocycle

Chizhov¹,

Engelhard²,

Chernavskii³

et al. 1992

Biophysical Journal

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The temperature and pH dependencies of the O(640) intermediate of the photocycle of bacteriorhodopsin (bR) were investigated by flash photolysis and T-jump experiments. The maximal concentration of the O(640) intermediate was found to be dependent on the temperature, which is described by a sigmoidal relationship. With increasing pH the midpoint of the sigmoidal curves shifts to higher temperatures. The Van't Hoff equation provides enthalpy and entropy values of the observed states. These results indicate that, in the investigated temperature (0-60 degrees C) and pH (pH 4.0-10.0) range, the sequence of the principal intermediates in the pathway "M-N-O-bR" does not change. The observations of the O(640) intermediate at pH < 8.0 and of the N(550) intermediate at pH > 8.0 are most probably due only to changes of the intrinsic rate constants of the bR photocycle, not to a different mechanism.

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Branching in the Bacteriorhodopsin Photochemical Cycle

Cited by 32 publications

References 15 publications

A correlation between proton pumping and the bacteriorhodopsin photocycle.

A correlation between proton pumping and the bacteriorhodopsin photocycle.

PICOSECOND KINETICS and A MODEL FOR THE PRIMARY EVENTS OF BACTERIORHODOPSIN

Temperature and pH sensitivity of the O640 intermediate of the bacteriorhodopsin photocycle

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