Chlorosomes from Chloroflexaceae typically have a ratio BChl c:BChl a of 50

(Blankenship and Matsuura 2003), and the relatively large amount of BChl a with excited-state energy levels that are significantly below those of BChl c leads to fast excited-state population within the selleckchem baseplate (~10 ps, see also above). Transfer from baseplate to RC is a factor of ~50 faster than it would have been from BChl c purely for entropic reasons because N total/N transfer is a factor of 50 smaller for BChl a as compared to BChl c. Of course, this is a simplified view because also other factors play GSI-IX manufacturer a role like overlap of donor emission and acceptor absorption spectra and relative orientations of the transition dipole moments. By increasing the number of BChl a molecules in the baseplate, the rate of extracting excitations from the BChl c pool will increase (also for entropic reasons) but on the other hand it will decrease the transfer to the RC because of lowering the ratio N total/N transfer. It is clear that the ratio of BChl c to Bchl a is an important parameter for determining the efficiency of EET towards the RC but as far as we know no systematic research has been reported on this issue. In this respect, it might be interesting to note that for Chlorobiaceae the BChl c to Bchl a ratio is a factor of 10 higher, i.e. it is around 500 (Blankenship

and Matsuura 2003). The third category of pigments in chlorosomes is the one of the carotenoids, constituting ~8% of the total amount SN-38 research buy of pigments in chloroflexaceae and ~4% in chlorobiaceae (Blankenship and Matsuura 2003). They transfer excitation energy to the BChls and, for instance, in Cf. aurantiacus a transfer efficiency to BChl c of 65% was reported (Van Dorssen et al. 1986), implying that at least 65% of the 3-oxoacyl-(acyl-carrier-protein) reductase carotenoids should be in Van der Waals contact with BChl c. Direct interactions

between BChls and carotenoids have also been inferred from changes in the BChl Stark spectrum (Frese et al. 1997) and the BChl absorption spectrum in the absence of carotenoids (Arellano et al. 2000; Kim et al. 2007). On the other hand, the carotenoids also protect chlorosomes against photodegradation and it was found that carotenoid-free chlorosomes photodegrade approximately three times faster than wild-type ones (Kim et al. 2007). However, no proof for BChl c triplet quenching by carotenoids could be found in Cf. aurantiacus and C. tepidum (Carbonera et al. 2001), whereas Arellano and coworkers found evidence for BChl a triplet quenching by carotenoids but not for BChl e triplet quenching in Chlorobium phaeobacteroides strain CL1401 (Arellano et al. 2000). Triplet quenching of (B)Chls by nearby carotenoids is usually occurring in photosynthetic light-harvesting systems to avoid the formation of deleterious singlet oxygen.