Effect of quinones on formation and properties of bacteriochlorophyll c aggregates

• Published in: Photosynthesis research 2008-02, Vol.95 (2-3), p.183-189
• Main Authors: Alster, Jan, Zupcanova, Anita, Vacha, Frantisek, Psencik, Jakub
• Format: Article
• Language: English
• Subjects: Bacteria; Bacterial Proteins - metabolism; Bacteriochlorophyll aggregates; Bacteriochlorophylls - metabolism; Biochemistry; Biomedical and Life Sciences; Chlorobium - metabolism; Chlorobium tepidum; Chlorophyll; Chlorosomes; Green sulphur bacteria; Life Sciences; Photosynthesis; Plant biology; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; quinones; Quinones - metabolism; Redox-dependent excitation quenching; Regular Paper; Spectrometry, Fluorescence
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-007-9259-9

Chlorosomes of green photosynthetic bacterium Chlorobium tepidum contain aggregates of bacteriochlorophyll c (BChl c) with carotenoids and isoprenoid quinones. BChl aggregates with very similar optical properties can be prepared also in vitro either in non-polar solvents or in aqueous buffers with addition of lipids and/or carotenoids. In this work, we show that the aggregation of BChl c in aqueous buffer can be induced also by quinones (vitamin K₁ and K₂), provided they are non-polar due to a hydrophobic side-chain. Polar vitamin K₃, which possess the same functional group as K₁ and K₂, does not induce the aggregation. The results confirm a principal role of the hydrophobic interactions as a driving force for the aggregation of chlorosomal BChls. The chlorosomal quinones play an important role in a redox-dependent excitation quenching, which may protect the cells against damage under oxygenic conditions. We found that aggregates of BChl c with vitamin K₁ and K₂ exhibit an excitation quenching as well. The amplitude of the quenching depends on quinone concentration, as determined from fluorescence measurements. No lipid is necessary to induce the quenching, which therefore originates mainly from interactions of BChl c with quinones incorporated in the aggregate structure. In contrast, only a weak quenching was observed for dimers of BChl c in buffer (either with or without vitamin K₃) and also for BChl c aggregates prepared with a lipid (lecithin). Thus, the weak quenching seems to be a property of BChl c itself.