Low-Temperature Optical and Resonance Raman Spectra of a Carotenoid Cation Radical in Photosystem II

John S. Vrettos, David H. Stewart, Julio C. De Paula, Gary W Brudvig

Research output: Contribution to journalArticle

64 Citations (Scopus)


Low-temperature (77 K) illumination of manganese-depleted Synechocystis PCC 6803 photosystem II core complexes caused the reversible photooxidation of a carotenoid, forming a carotenoid cation radical with an absorbance maximum at 984 nm. Resonance FT-Raman spectra obtained with 1064 nm excitation gave a spectrum characteristic of carotenoid cation radicals in solution. This is the first example of a resonance Raman spectrum of a carotenoid cation radical in a protein. The carotenoid photooxidation requires prior chemical oxidation of cytochrome b559 which implicates the carotenoid in the secondary electron-transfer pathway of photosystem II that may play a role in photoprotection. The possible nature of the pathway and the structure of the carotenoid cation radical are discussed.

Original languageEnglish
Pages (from-to)6403-6406
Number of pages4
JournalJournal of Physical Chemistry B
Issue number31
Publication statusPublished - Aug 5 1999


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this