tepidum, the Y-axis of BChl c along which the Q y transition dipole moment is oriented makes an angle of 55° with the local cylinder axis (Ganapathy et al. 2009). This means that the LD integrated over the Q y band should be very close to zero. Due to exciton coupling, the LD is again expected to be positive on the long-wavelength side and to keep the integrated LD close to zero this should then be compensated

by negative LD on the short-wavelength side. Linear-dichroism spectra of these particular chlorosomes have not been presented in literature. selleck products There is one more issue that should be clarified and this concerns the Stark spectrum of chlorosomes. Chls and BChls possess a difference dipole moment Δµ between ground and excited (Q y) state that is responsible for a feature in the Stark spectrum with the shape of the second-derivative of the absorption spectrum (see, e.g. Boxer, 2009). The intensity of this contribution is a measure for the value of Δµ. Remarkably, in contrast to all the known Stark spectra of photosynthetic complexes, there is no such

feature for the Q y absorption band and Δµ is equal to 0 (Frese et al. 1997). This has been explained by an antiparallel eFT508 molecular weight organization of strongly coupled BChl c molecules in the chlorosome, either because of antiparallel-dimer building blocks or because of the presence of antiparallel linear stacks. Such an antiparallel organization is not present in the model for Depsipeptide the chlorosomes of triple mutant of C. tepidum mentioned above (Ganapathy et al. 2009). Therefore, it is expected that Stark measurements on these chlorosomes will show second-derivative character in the Q y region and together with the LD measurements they might form another way of testing the current model. Finally, it is worthwhile to point out that the lamellar model that was proposed by Pšenčík et al. (2004) cannot explain the pronounced CD spectra

of chlorosomes (Linnanto and Korppi-Tommola 2008) although the authors could not rule out the simultaneous presence of lamellar and cylindrical structures. According to the most recent EM data presented above, such a coexistence seems indeed to be the case (Ganapathy et al. 2009; Oostergetel et al. 2007). Closing remarks In conclusion, chlorosomes are fascinating organelles because of their amazing capacity of light harvesting. The need for harvesting a broad range of the spectrum of light constrains the composition of the BChl molecules and the amount of order in the packing, for which now a consistent model is available. This model describes the molecular and supramolecular packing and can be further tested, for instance, with LD, which will provide LY333531 order useful information on the long-range ordering of the pigments. An intriguing feature is the thin envelope which consists of only one membrane leaflet, an uncommon phenomenon in nature.