Comparison of the absorption spectra of trimers and aggregates of chlorophyll a/b light-harvesting complex LHC II

K. Razi Naqvi, T. B. Melø, B. Bangar Raju, Tamás Jávorfi, Gyözö Garab

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The absorption spectrum of a suspension containing aggregates of LHC II, the light-harvesting chlorophyll a/b-protein complex associated with photosystem II, when corrected for distortions introduced by scattering and mutual shadowing of trimers within a single aggregate, turns out to be almost superposable on the absorption spectrum recorded after disrupting the aggregates by the addition of a detergent at a concentration close to its critical micelle concentration (CMC). The correction for scattering is effected by implementing a strategy proposed in 1962 by Latimer and Eubanks; that for shadowing, by using a relation derived by Duysens in 1956, which also furnishes an estimate of the aggregate size. The standard procedure for bringing down scattering-related distortions, namely the use of an opal-glass plate, is found to be unsatisfactory for LHC II samples. Extinction spectra (i.e. scattering-contaminated experimental absorption spectra), recorded over a limited range of the detergent concentration (lying between zero and the CMC), are found to pass through two isosbestic points, which differ from their counterparts in true absorption spectra: being points at which total extinction stays constant, their locations depend on the instrumental geometry as well as on the size of the aggregates.

Original languageEnglish
Pages (from-to)1925-1936
Number of pages12
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Issue number11
Publication statusPublished - Oct 1 1997



  • Absorption flattening
  • Light-harvesting complex
  • Photosynthesis
  • Selective scattering
  • Sieve effect

ASJC Scopus subject areas

  • Analytical Chemistry
  • Atomic and Molecular Physics, and Optics
  • Instrumentation
  • Spectroscopy

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