Gas-phase photochemistry of the photoactive yellow protein chromophore trans-p-coumaric acid

Wendy L Ryan, David J Gordon, Donald H Levy

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


The photoisomerization of trans-p-coumaric acid (trans-CA) triggers a photocycle in photoactive yellow protein that ultimately mediates a phototactic response to blue light in certain purple bacteria. We have used fluorescence excitation and dispersed emission methods in a supersonic jet to investigate the nature of the electronic excited states involved in the initial photoexcitation and subsequent photoisomerization of trans-CA. We observed three distinct regions in the fluorescence excitation spectrum of trans-CA. Region I is characterized by sharp features that upon excitation exhibit trans-CA S(1) emission. In region II, features increase in width and decrease in intensity with increasing excitation energy. Upon excitation, we observed dual emission from the S(1) state of trans-CA and what may be the S(1) state of cis-CA. The onset of dual emission corresponds to an isomerization barrier of about 3.4 kcal/mol. Finally, the extremely broad absorption feature in region III is excitation to the S(2) electronic excited state and excitation results in trans-CA S(1) emission. Furthermore, we collected CA from the molecular beam after laser excitation in each of the three regions as further evidence of the photoisomerization process. The relative amounts of trans- and cis-CA in the collected molecules were measured with high-pressure liquid chromatography. Although trans-CA was excited in all three regions, a significant cis-CA peak appeared only in region II, though a small cis peak was observed in region III.

Original languageEnglish (US)
Pages (from-to)6194-201
Number of pages8
JournalJournal of the American Chemical Society
Issue number21
StatePublished - May 29 2002
Externally publishedYes


  • Bacterial Proteins/chemistry
  • Chromatography, High Pressure Liquid
  • Coumaric Acids/chemistry
  • Gases
  • Photochemistry
  • Photoreceptors, Microbial
  • Protein Conformation
  • Spectrometry, Fluorescence

PubMed: MeSH publication types

  • Journal Article


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