Deciphering excited state evolution in halorhodopsin with stimulated emission pumping

Oshrat Bismuth, Pavel Komm, Noga Friedman, Tamar Eliash, Mordechai Sheves*, Sanford Ruhman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

The primary photochemical dynamics of We. pharaonis Halorhodopsin (pHR) are investigated by femtosecond visible pump-near IR dump-hyperspectral probe spectroscopy. The efficiency of excited state depletion is deduced from transient changes in absorption, recorded with and without stimulated emission pumping (SEP), as a function of the dump delay. The concomitant reduction of photocycle population is assessed by probing the "K" intermediate difference spectrum. Results show that the cross section for stimulating emission is nearly constant throughout the fluorescent state lifetime. Probing "K" demonstrates that dumping produces a proportionate reduction in photocycle yields. We conclude that, despite its nonexponential internal conversion (IC) kinetics, the fluorescent state in pHR constitutes a single intermediate in the photocycle. This contrasts with conclusions drawn from the study of primary events in the related chloride pump from Hb. salinarum (sHR), believed to produce the "K" intermediate from a distinct short-lived surpopulation in the excited state. Our discoveries concerning internal conversion dynamics in pHR are discussed in light of recent expectations for similar excited state dynamics in both proteins.

Original languageEnglish
Pages (from-to)3046-3051
Number of pages6
JournalJournal of Physical Chemistry B
Volume114
Issue number8
DOIs
StatePublished - 4 Mar 2010

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