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

Abstract

Abstract-The CD spectra of a range of antenna complexes from several different species of purple photosynthetic bacteria were recorded in the wavelength range of 190 to 930 nm. Analysis of the far UV CD (190 to 250 nm) showed that in each case except for the B800-850 from Chr. vinosum the secondary structure of the light-harvesting complexes contains a large amount of a-helix ( 2 5 0 % ) and very little p-pleated sheet. This confirms the predictions of the group of Zuber of a high a-helical content based upon consideration of the primary structures of several antenna apoproteins. The CD spectra from the carotenoids and the bacteriochlorophylls show considerable variations depending upon the type of antenna complex. The different amplitude ratios in the CD spectrum for the bacteriochlorophyll Qy, Qx and Soret bands indicate not only different degrees of exciton coupling, but also a strong and variable hyperchromism (Scherz and Parson, 1984a, b).

Crystallization of two integral membrane pigment–protein complexes from the purple‐sulfur bacterium Chromatium purpuratum

“…The basic structure of all LHs is thought to be a heterodimer of the small a and polypeptides (5-10 kDa) that bind pigments in a specific stoichiometry distinctive of LH1 or LH2. Sequence analysis and circular dichroism measurements of antenna complexes of purple-nonsulfur bacteria suggest that each LH1 or LH2 antenna polypeptide spans the membrane once in the form of an a-helix (Cogdell & Scheer, 1985;Brunisholz et al, 1986). The limited biochemical data on purple-sulfur organisms (members of the Chromatiaceae) indicate subunit homology at the level of function and of primary sequence (Bissig et al, 1990;Kerfeld et al, manuscripts submitted and in prep.…”

Determination of the Molar Extinction Coefficients of the B800 and B850 Absorption Bands in Light-harvesting Complexes 2 Derived from Three Purple Photosynthetic Bacteria Rhodoblastus acidophilus, Rhodobacter sphaeroides, and Phaeospirillum molischianum by Extraction of Bacteriochlorophyll a

“…[11][12][13][14][15][16][17][18][19][20] Such confusion would originate from poor experimental evidence and/or chain citations; some reports just referred to the previous publications for the ε values of LH2. Therefore, it is necessary to reconsider the ε values of the B800 and B850 bands of the LH2 proteins based on precise experimental measurements.…”

“…To the best of our knowledge, four research groups actually estimated the molar extinction coefficients of LH2 from Rba. sphaeroides, [12][13][14] Rbl. acidophilus, 13,15 and Allochromatium (Alc.)…”

“…sphaeroides, [12][13][14] Rbl. acidophilus, 13,15 and Allochromatium (Alc.) vinosum (formerly known as Chromatium vinosum) 13 as summarized in Table S1 (Supporting Information).…”

“…acidophilus, 13,15 and Allochromatium (Alc.) vinosum (formerly known as Chromatium vinosum) 13 as summarized in Table S1 (Supporting Information). However, the lack of structural information on the LH2 proteins, including the number of pigments per protein, would require some assumptions and/or a little circuitous measurements for the estimation of the ε values.…”