scholarly journals Transfer of Genes Coding for Apoproteins of Reaction Centre and Light-harvesting LH1 Complexes to Rhodobacter sphaeroides

Microbiology ◽  
1988 ◽  
Vol 134 (6) ◽  
pp. 1471-1480 ◽  
Author(s):  
C. N. Hunter ◽  
G. Turner
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Light Harvesting ◽  
Reaction Centre

scholarly journals Effect of oxygen on levels of mRNA coding for reaction-centre and light-harvesting polypeptides of Rhodobacter sphaeroides

1987 ◽  
Vol 247 (2) ◽  
pp. 489-492 ◽  
Author(s):  
C N Hunter ◽  
M K Ashby ◽  
S A Coomber
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Light Harvesting ◽  
Photosynthetic Apparatus ◽  
Maximum Level ◽  
Reaction Centre ◽  
Puf Operon ◽  
Effect Of Oxygen

The relative levels of mRNA for the reaction-centre L and M subunits, B875 (LH1) alpha and beta polypeptides and B800-850 (LH2) alpha and beta polypeptides, have been measured during pigment induction of Rhodobacter sphaeroides. Over the 6 h of the experiment, bacteriochlorophyll levels increased by at least 100-fold. No transcripts for photosynthetic components were detectable at the start of induction; after 2 h the levels of transcripts from the puf operon (encoding reaction-centre and B875 subunits) had reached the maximum; these transcripts were 2.7 and 0.5 kb respectively. The transcript for the puc operon (B800-850 complex) was estimated to be 0.55 kb and reached a maximum level after 6 h. These results are consistent with the proposal that, during the assembly of the photosynthetic apparatus, the synthesis of B875 reaction-centre aggregates precedes that of the major antenna, B800-850.

scholarly journals Cryo-EM structure of the Rhodobacter sphaeroides RC-LH1 core monomer complex at 2.5 Å

2021 ◽  
Author(s):  
Pu Qian ◽  
David JK Swainsbury ◽  
Tristan Ian Croll ◽  
Jack H Salisbury ◽  
Elizabeth C Martin ◽  
...  
Keyword(s):  
Rhodobacter Sphaeroides ◽  
Light Harvesting ◽  
Ring Structure ◽  
Bacterial Photosynthesis ◽  
Reaction Centre ◽  
Cytochrome Bc1 Complex ◽  
Protein Subunit ◽  
Proton Transfers ◽  
Monomeric Complex ◽  
Essential Components

Reaction centre light-harvesting 1 (RC-LH1) complexes are the essential components of bacterial photosynthesis. The membrane-intrinsic LH1 complex absorbs light and the energy migrates to an enclosed RC where a succession of electron and proton transfers conserves the energy as a quinol, which is exported to the cytochrome bc1 complex. In some RC-LH1 variants quinols can diffuse through small pores in a fully circular, 16-subunit LH1 ring, while in others missing LH1 subunits create a gap for quinol export. We used cryogenic electron microscopy to obtain a 2.5 Å resolution structure of one such RC-LH1, a monomeric complex from Rhodobacter sphaeroides. The structure shows that the RC is partly enclosed by a 14-subunit LH1 ring in which each αβ heterodimer binds two bacteriochlorophylls and, unusually for currently reported complexes, two carotenoids rather than one. Although the extra carotenoids confer an advantage in terms of photoprotection and light harvesting, they could block small pores in the LH1 ring and impede passage of quinones, necessitating a mechanism to create a dedicated quinone channel. The structure shows that two transmembrane proteins play a part in stabilizing an open ring structure; one of these components, the PufX polypeptide, is augmented by a hitherto undescribed protein subunit we designate as protein-Y, which lies against the transmembrane regions of the thirteenth and fourteenth LH1α polypeptides. Protein-Y prevents LH1 subunits 11-14 adjacent to the RC QB site from bending inwards towards the RC and, with PufX preventing complete encirclement of the RC, this pair of polypeptides ensures unhindered

Spectroscopic methods in photosynthesis: photosystem stoichiometry and chlorophyll antenna size

1989 ◽  
Vol 323 (1216) ◽  
pp. 397-409 ◽  
Keyword(s):  
Plant Species ◽  
Light Harvesting ◽  
Electron Flow ◽  
Vascular Plant ◽  
Thylakoid Membranes ◽  
Reaction Centre ◽  
Antenna Size ◽  
Fluorescence Measurements ◽  
Photosystem Stoichiometry ◽  
Absorption Of Light

Light-induced absorbance change and fluorescence measurements were employed in the quantitation of photosystem stoichiometry and in the measurement of the chlorophyll (Chl) antenna size in thylakoid membranes. Results with thylakoid membranes from diverse photosynthetic tissues indicated a PSII/PSI reaction-centre stoichiometry that deviates from unity. Cyanobacteria and red algae have a PSII/PSI ratio in the range of 0.3 to 0.7. Chloroplasts from spinach and other vascular-plant species grown under direct sunlight have PSII/PSI = 1.8±0.3. Chlorophyll b -deficient and Chi b -lacking mutants have PSII/PSI > 2. The observation that PSII/PSI ratios are not unity and show a large variation among different photosynthetic membranes appears to be contrary to the conventional assumption derived from the Z-scheme. However, the photosystem stoichiometry is not the only factor that needs to be taken into account to explain the coordination of the two photosystems in the process of linear electron transport. The light-harvesting capacity of each photosystem must also be considered. In cyanobacterial thylakoids (from Synechococcus 6301, PSII/PSI = 0.5±0.2), the phycobilisome-PSII complexes collectively harvest as much light as the PSI complexes. In vascular plant chloroplasts, the light-harvesting capacity of a PSI I complex (250 molecules, Chi a/Chi b = 1.7) is lower than that of a PSI complex (230 Chl, Chl a /Chl b = 8.0) because Chi b has a lower extinction coefficient than Chi a . A differential attenuation of light intensity through the grana further reduces the light absorbed by PSII. Hence, a PSII/PSI ratio greater than one in vascular-plant chloroplasts compensates for the lower absorption of light by individual PSII complexes and ensures that, on average, PSII will harvest about as much light as PSI. In conclusion, distinct light-harvesting strategies among diverse plant species complement widely different photosystem stoichiometries to ensure a balanced absorption of light and a balanced electron flow between the two photoreactions, thereby satisfying the requirement set forth upon the formulation of the Z-scheme by Hill & Bendall ( Nature, Lond. 186, 136-137 (1960)) and by Duysens, Amesz & Kamp ( Nature, Lond . 190, 510-511 (1961)).

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