Pigment organization and energy transfer in green bacteria. 2. Circular and linear dichroism spectra of protein-containing and protein-free chlorosomes isolated from Chloroflexus aurantiacus strain Ok-70-fl

Abstract

We have measured the circular dichroism (CD) and linear dichroism (LD) spectra of chlorosomes isolated from Chloroflexus aurantiacus strain Ok-70-fl obtained by two different isolation procedures. The gel-electrophoretic filtration procedure yields chlorosomes that are essentially free of BChl a 790 and proteins, while isolation by sucrose density gradient centrifugation yields the conventional chlorosome preparations. The LD spectra of the two kinds of preparation were very similar. In both cases the Q y LD signals correspond to an average angle between the BChl- c -Q y transition and the long axis of the chlorosome of approx. 15 ± 10°. In contrast to the LD spectra, the CD spectra of different preparations (membranes, BChl- a -free chlorosomes, BChl- a -containing chlorosomes) show pronounced differences both in the ellipticity as well as in the shape of the spectra and the number of maxima. However, these differences are not caused by the isolation procedure or the detergents used. We show that even freshly prepared membranes (of different, parallel grown batch cultures) give rise to very different CD spectra. The set of different CD spectra we obtained could be simulated well by linear combinations of two basic spectra. This strongly suggests that the variations in the CD spectra are caused by a variation in the relative amounts of two different species, two different types of chlorosome, or possibly by two different types of pigment aggregate within the chlorosomes.