Spectroscopic studies of phycobilisome subcore preparations lacking key core chromophores: Assignment of excited state energies to the Lcm, β18 and αAP-B chromophores

Yvonne M. Gindt, Jianhui Zhou, Donald A. Bryant, Kenneth Sauer

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Abstract

Chromophore absorption and emission characteristics of the αAP-B, β18 and Lcm (large core-membrane linker) chromopeptides within the phycobilisome core are investigated using genetically engineered strains of Synechococcus sp. PCC 7002. Steady-state and time-resolved emission were used to examine energy transfer in subcore preparations from the wild-type organism and two mutants. Low-temperature (77 K) emission spectra were also measured for intact phycobilisomes from the wild-type and five mutant strains. Mutants retaining either the αAP-B subunit or the unaltered Lcm chromophore resulted in only small changes in the low-temperature emission spectra, while retention of only the β18 subunit resulted in blue-shifted emission spectra. The Lcm chromophore has a room-temperature absorption maximum at 675 nm. In phycobilisomes at 77 K the αAP-B and Lcm chromophores emit at 682-683 nm, and they are the best candidates for long-wavelength emitters also at room temperature. Overlap of these emission spectra with the absorption of chlorophyll a in the associated thylakoid membrane plays a significant role in excitation transfer from the antenna complexes in cyanobacteria.

Original languageEnglish
Pages (from-to)153-162
Number of pages10
JournalBBA - Bioenergetics
Volume1186
Issue number3
DOIs
StatePublished - 29 Jul 1994

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Keywords

  • Cyanobacterium
  • Energy transfer
  • Fluorescence relaxation
  • Phycobilisome
  • Subcore particle, 18 S

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