We have used time-resolved absorption and fluorescence spectroscopy with nanosecond resolution to study triplet energy transfer from chlorophylls to carotenoids in a protective process that prevents the formation of reactive singlet oxygen. The light-harvesting complexes studied were isolated from Chromera velia, belonging to a group Alveolata, and Xanthonema debile and Nannochloropsis oceanica, both from Stramenopiles. All three light-harvesting complexes are related to fucoxanthin-chlorophyll protein, but contain only chlorophyll a and no chlorophyll c. In addition, they differ in the carotenoid content. This composition of the complexes allowed us to study the quenching of chlorophyll a triplet states by different carotenoids in a comparable environment. The triplet states of chlorophylls bound to the light-harvesting complexes were quenched by carotenoids with an efficiency close to 100%. Carotenoid triplet states were observed to rise with a ~5 ns lifetime and were spectrally and kinetically homogeneous. The triplet states were formed predominantly on the red-most chlorophylls and were quenched by carotenoids which were further identified or at least spectrally characterized.

• Klíčová slova
• Algae, Energy transfer, Light harvesting, Photoprotection, Photosynthesis, Transient spectroscopy,
• MeSH
• anaerobióza MeSH
• časové faktory MeSH
• chlorofyl metabolismus   MeSH
• fluorescenční spektrometrie MeSH
• fotochemické procesy * MeSH
• Heterokontophyta metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• kinetika MeSH
• proteiny vázající chlorofyl metabolismus   MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• chlorofyl MeSH
• karotenoidy MeSH
• proteiny vázající chlorofyl MeSH
• světlosběrné proteinové komplexy MeSH

The green filamentous bacterium Chloroflexus aurantiacus employs chlorosomes as photosynthetic antennae. Chlorosomes contain bacteriochlorophyll aggregates and are attached to the inner side of a plasma membrane via a protein baseplate. The structure of chlorosomes from C. aurantiacus was investigated by using a combination of cryo-electron microscopy and X-ray diffraction and compared with that of Chlorobi species. Cryo-electron tomography revealed thin chlorosomes for which a distinct crystalline baseplate lattice was visualized in high-resolution projections. The baseplate is present only on one side of the chlorosome, and the lattice dimensions suggest that a dimer of the CsmA protein is the building block. The bacteriochlorophyll aggregates inside the chlorosome are arranged in lamellae, but the spacing is much greater than that in Chlorobi species. A comparison of chlorosomes from different species suggested that the lamellar spacing is proportional to the chain length of the esterifying alcohols. C. aurantiacus chlorosomes accumulate larger quantities of carotenoids under high-light conditions, presumably to provide photoprotection. The wider lamellae allow accommodation of the additional carotenoids and lead to increased disorder within the lamellae.

• MeSH
• bakteriální chromatofory MeSH
• bakteriochlorofyly fyziologie   MeSH
• buněčná membrána MeSH
• Chloroflexus metabolismus   MeSH
• difrakce rentgenového záření MeSH
• intracelulární membrány MeSH
• organely fyziologie   ultrastruktura   MeSH
• světlosběrné proteinové komplexy fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• bakteriochlorofyly MeSH
• světlosběrné proteinové komplexy MeSH