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Studies on energy dissipation in phycobilisomes using the Kennard-Stepanov relation between absoption and fluorescence emission spectra

Author:
  • Lars Olof Björn
  • G S Björn
Publishing year: 1986
Language: English
Pages: 535-542
Publication/Series: Photochemistry and Photobiology
Volume: 44
Issue: 4
Document type: Journal article
Publisher: American Society for Photobiology

Abstract english

Absorption and fluorescence emission spectra were measured at room temperature (ca. 22.degree.C) for solutions of phycocyanin-1, phycocyanin-2, and allophycocyanin from Phormidium luridum, and also for phycobilisome preparations from various blue-green algae (Anabaena variabilis, Nostoc muscorum strain A, Nostoc sp. strain Mac. Phormidium luridum). Kennard-Stepanov (KS) temperatures (T) were computed using the Kennard-Stepanov relationship F(.lambda.) = b A (.lambda.) (.lambda.-5 exp(-hc/.lambda.kT), where F(.lambda.) stands for fluorescence (energy per wavelength interval) as a function of wavelength (.lambda.), A(.lambda.) is absorbance as a function of wavelength, b a proportionality factor, and h, c and k are Planck's constant, the velocity of light and Boltzmann's constant, respectively. In most cases experimental data followed the expected relationship, but at low ionic strength allophycocyanin gave a clearly biphasic KS plot, i.e. In .lambda.5 F(.lambda.)/A(.lambda.) vs l /.lambda.. This could be due to the presence of both monomers and trimers in the sample at low ionic strength. For purified allophycocyanin and phycocyanins (PC-1 and PC-2) as well as phycobilisomes from Phormidium luridum, the KS temperatures were only slightly (insignificantly) elevated above the sample temperature. Thus, after absorption of a photon, vibrational and configurational equilibration is essentially completed before emission of the fluorescence photon takes place. For phycobilisomes from Anabaena variabilis and the two Nostoc species the KS temperatures were moderately elevated. Since there was no correlation between radiation temperature and excitation wavelength, the elevation is not due to excess (undissipated) vibrational energy, but rather to incomplete configurational equilibration.

Keywords

  • Biological Sciences

Other

Published
  • ISSN: 0031-8655
Lars Olof Björn
E-mail: lars_olof [dot] bjorn [at] biol [dot] lu [dot] se

Professor emeritus

Molecular Cell Biology

+46 46 222 72 53

B-A340

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