Quenching of bacteriochlorophyll fluorescence in chlorosomes from Chloroflexus aurantiacus by exogenous quinones

The quenching of bacteriochlorophyll (BChl) c fluorescence in chlorosomes i solated from Chloroflexus aurantiacus was examined by the addition of vario us benzoquinones, naphthoquinones (NQ), and anthraquinones (AQ), Many quino nes showed strong quenching in the micromolar or submicromolar range, The n umber of quinone molecules bound to the chlorosomes was estimated to be as small as one quinone molecule per 50 BChl c molecules. Quinones which exhib it a high quenching effect have sufficient hydrophobicity and one or more h ydroxyl groups in the alpha positions of NQ and AQ, Chlorobiumquinone has b een suggested to be essential for the endogenous quenching of chlorosome fl uorescence in Chlorobium tepidum under oxic conditions. We suggest that the quenching effect of chlorobiumquinone in chlorosomes from Chl. tepidum is related to the 1'-oxo group neighboring the dicarbonyl group.