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Protonation of a novel intermediate P is involved in the M → bR step of the bacteriorhodopsin photocycle
Author(s) -
Drachev L.A.,
Kaulen A.D.,
Skulachev V.P.,
Zorina V.V.
Publication year - 1986
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(86)81134-6
Subject(s) - bacteriorhodopsin , protonation , chemistry , absorption (acoustics) , molar absorptivity , absorption spectroscopy , photochemistry , halobacteriaceae , proton , crystallography , deprotonation , schiff base , analytical chemistry (journal) , halobacterium salinarum , membrane , chromatography , ion , materials science , organic chemistry , optics , biochemistry , physics , quantum mechanics , composite material
A novel intermediate (P) of the bacteriorhodopsin (bR) photocycle, appearing between M412 and bR is described. Like bR, intermediate P shows an absorption maximum at 560–570 nm. However, the extinction coefficient of P is somewhat lower than that of bR. Moreover, there are some differences in spectra of bR and P at wavelengths shorter than 450 nm. The P → bR transition correlates with the absorption of H + from the water medium. The following conditions proved to be favourable for the detection of the new intermediate: a high salt concentration, low light intensity and low temperature (0.5°C). The P → bR transition is strongly decelerated by a small amount of Triton X‐100. Illumination of P does not produce M412 before bR is formed. It is assumed that M412 converts to P when the Schiff base is protonated by a proton transferred from a protein protolytic group which participates in the inward H + ‐conductivity pathway. Reprotonation of this group results in the conversion of P to bR. No more than 1 H + is transported per bR photocycle.