THE INWARD H+ PATHWAY IN BACTERIORHODOPSIN: THE ROLE OF M412 AND P(N)560 INTERMEDIATES* |
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Authors: | S V Danshina L A Drachev † A D Kaulen V P Skulachev |
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Institution: | A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia |
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Abstract: | Abstract— In purple bacteriorhodopsin sheets adsorbed onto the phospholipid-impregnated collodion film, electrogenic stages are identified correlating with decays of the M and N(P)-type intermediates. It is concluded that both M → N and N → bR transitions are electrogenic. The M decay is shown to be of a complex kinetics. In purple sheets, the lower the light intensity, the higher the rate of "slow M" decay. Such a dependence, which is absent from monomeric bacteriorhodopsin in proteoliposomes and from Triton X-100-solubilized protein, may be explained by the inhibiting effect of a light-induced conformation change in a bacteriorhodopsin molecule upon the M decay in some other bacteriorhodopsin molecules within the same sheet. The light intensity-independent "slow M" decay in solubilized bacteriorhodopsin is shown to correlate with the decay of the N intermediate and H+ uptake after the flash. In contrast to "fast M", "slow M" is pH dependent, closely resembling in this respect the N intermediate. It is suggested that there is a fast light-independent equilibration between M and N so that "slow M" represents the portion of the M pool that monitors the N concentration. The M → N equilibrium is assumed to be involved in the effect of the light-induced electric field on the M decay. No direct effect of light on the equilibrium was found. |
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