Thermal equilibration between the M and N intermediates in the photocycle of bacteriorhodopsin

S. Druckmann, M. P. Heyn, J. K. Lanyi, M. Ottolenghi, L. Zimanyi

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The stages in the photocycle of bacteriorhodopsin (BR) involving the M and N intermediates are investigated using a double pulse excitation method. A first (cycling) pulse at 532 nm is followed, with an appropriate time delay, by a second pulse (337, 406, 446, or 470 nm) which induces the M-->BR back-photoreaction. After depletion by the second pulse a repopulation of M in the millisecond range is observed which is interpreted in terms of a thermal N-->M relaxation. It is thus concluded that a (thermal) M<-->N equilibrium accounts for the biphasic decay of M in the BR photocycle. Other models for this stage of the light-driven proton-pump are therefore unnecessary.

Original languageEnglish
Pages (from-to)1231-1234
Number of pages4
JournalBiophysical journal
Issue number3
Publication statusPublished - Jan 1 1993


ASJC Scopus subject areas

  • Biophysics

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