Rhodopin glucoside

Estimated by scaling the rhodopin glucoside Si-Bchl Qy electronic couplings in LH2 of Rps. acidophila calculated by the TDC method [83]. 

Figure 9. A comparison of transition densities for rhodopin glucoside calculated using TDDFT (6-31++g basis set). On the right the So —> S2 transition is shown, with its large dipole transition moment being evidenced by the change in sign of this TD from one end of the molecule to the other. On the left the So — Si transition is shown. The symmetry of the TD causes the transition to be optically forbidden. See color insert.

Proteobacteria (Imhoff, 1995). The functions of carotenoids in photosynthetic bacteria have been investigated in most detail in the Rhodospirillaceae (other chapters in this book). Their RC resembles that of PS 11 of green plants. Their major BChl is BChl a or b. The RC was firstly crystallized from Bla. (previously, Rhodopseudomonas) viridis, and the localization of one carotenoid, 1,2-dihydroneuro-sporene, four BChl b and two bacteriopheophytin b molecules was determined (Deisenhofer et al., 1995). A similar localization of spheroidene in the RC of Rba. sphaeroides has also been described (Yeates et al., 1988 Ermler et al., 1994). The fine crystal structure of the LH II antenna complex from Rps. acidophila strain 10050 has shown the localization of one rhodopin glucoside and three BChl a molecules per ap monomer (McDermott et al., 1995). A similar localization of lycopene in the LH II complex from Rsp. molischiamm has also described (Koepke et al,... 

The absorption spectrum of the LH2 complex from Rps. acidophila is shown in Fig. 2. In the NIR two strong absorption peaks due to the Qy transition of BChl a are seen, one at -800 nm and the other at -860 nm (this complex is also called by the generic name B800-850). There are also two other prominent absorption bands due to BChl a, the Qx band at -590 nm and the Soret band at -380 nm. The three bands seen between 450 550 nm arise from the carotenoid, rhodopin-glucoside, which has 11 conjugated double bands. The BChls and the carotenoids are non-covalently bound to two low molecular weight, very... 

Fig. 4. A section of the structure of the LH2 complex from Rhodopseudomonas acidophila strain 10050 only showing the pigment. I n Color Plate 5 the representation is B850 BChi a/s - red, B800 BChl a/s - green, rhodopin glucoside - yellow. This figure was redrawn from McDermott et al. (1995). See also Color Plate 5.

Fig. 5. A schematic representation of the arrangement of the pigments in the LH2 complex from Rhodopseudomonas acidophila strain 10050 within one a/3 apoprotein pair. The rhodopin glucoside molecule can be seen coming into contact with the edge of the B800 BCh a molecule and passing over the face of the a-bound B850 BChl a molecule.

The initial description of the structure of LH2 (McDermottt et al., 1995) resolved a single molecule of rhodopin glucoside pera)3 apoprotein pair (Fig. 5). It has an extended sigmoidal shaped conformation and spans the whole depth of the complex. This conformationis atypical all-fran conformation (Fig. 

Fig. 6. A space filling model of the structure of rhodopin-glucoside in the LH2 complex from Rhodopseudomonas acidophila strain 10050. (Top) A side view (Bottom) A view looking down the long axis of the carotenoid.

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