Spectroscopic characterization of pigment binding proteins in normal-grownand iron-stressed thermophilic cyanobacteria Synecococcus sp.

The results of low temperature absorption, fluorescence and hole burning sp ectroscopy of pigment binding proteins in normal-grown and iron-stressed th ermophilic Synecococcus sp. are reported. These experiments revealed that t he growing of Synecococcus sp. under the iron-limited condition affects spe ctral characteristics and excited energy transfer (EET) in pigment proteins . The comparison of low temperature absorption spectra of normal-grown and ir on-stressed thermophilic cyanobacteria well documents major changes in comp osition of the antenna systems and in composition of the core of photosyste m II. The absorption of membrane chlorophyll in particular, is blue-shifted from 679 nm in normal cells to 673 nm which is caused by absorption of chlorophy ll binding protein CP 34 in stressed sample. The presence of CP 34 in the p hotosystem II (PS' IT) has also been seen in the low temperature fluorescen ce spectra where the increased luminescence at 685 nm has been observed. Th is implies the decreased efficiency of photosynthesis in iron-limited sampl e. We studied the energy transfer in PS II by the means of fluorescence and ab sorption hole-burning spectroscopy which enabled to study the influence of iron-stressed condition on energy transfer and pigment-protein interaction (Debye-Waller factor). The stressed cells exhibit the broadened spectral ho le: width at 682 and 685.5 nm. (C) 1999 Elsevier Science B.V. All rights re served.