Pigment organization of the B800–850 antenna complex of Rhodopseudomonas sphaeroides

Circular Dichroism of Light‐harvesting Complexes From Purple Photosynthetic Bacteria*

“…sphaeroides agrees well with those previously reported (Bolt and Sauer, 1981;Kramer et al, 1984;Sauer and Austin, 1978), while the CD spectrum of the 'type I' B800-850 complex from Rp. acidophila is more closely related to the CD spectrum of the "high" 850 complex from Rp.…”

“…Once they have been solubilized they can be isolated essentially free of other components. Depending on the detergent used, the size of the complexes varies considerably (Niedermann, 1983;van Grondelle et al, 1983;Kramer et al, 1984). The smallest functional unit (as defined by retention of the native absorption spectrum and efficient energy transfer among its pigments) usually has an apparent molecular weight of appx.…”

“…The smallest functional unit (as defined by retention of the native absorption spectrum and efficient energy transfer among its pigments) usually has an apparent molecular weight of appx. 100 kDa (Picorel et al, 1984;Peters and Drews, 1983a;Shiozawa et al, 1982;Miller, 1982;Jay et al, 1984;Kramer et al, 1984). This corresponds to an aggregate of about six of each of the individual subunits, 12-18 molecules 'Dedicated to the memory of Warren L. Butler.…”

“…CD data on bacteriochlorophyll a containing, membrane-derived complexes and/or membrane fractions is available for R p . sphaeroides (Bolt et al, 1981b;Kramer et al, 1984;Miyazaki et al, 1979), R p . palustris (Hayashi et al, 1982;Miyazaki and Morita, 198l), Rp.…”

8.5 Å Projection Map of the Light-Harvesting Complex I from Rhodospirillum Rubrum Reveals a Ring Composed of 16 Subunits

“…Part of the central density may be contributed by an edge-on view of a pair of BChl a molecules: (i) model calculations suggest that the red-shift observed for the absorption spectrum of the native complex arises principally from a strongly interacting dimer of BChl a (Pearlstein and Zuber, 1985;Rosenbach-Belkin et al, 1988); (ii) the dimensions of the central density correspond roughly to the sum of those observed for interacting chlorophyll dimers obtained by X-ray crystallography of several chlorophyll derivatives (Kratky and Dunitz, 1977); (iii) putative interacting BChl a dimers would be separated from their nearest neighbours by a distance of -7.5 A, which is within the critical distance (10 A) for efficient Forster energy transfer; (iv) the two conserved histidines 636 implicated in binding to the bacteriochlorophyll magnesium are predicted to be within the helical transmembrane segments of the polypeptides (Zuber, 1985); (v) linear dichroism data of chromatophores of R.rubrum suggest that both BChl a molecules of the ax-heterodimer are oriented parallel to the membrane normal (Kramer et al, 1984). This proposed arrangement with the bacteriochlorophylls sandwiched between the histidines of the xand ,-subunits therefore fits both the density map and the prior biochemical data well; the carotenoid, which has been shown to be bound almost parallel to the membrane plane, is unlikely to be resolved in this projection map.…”