Document Detail

The Accumulation of the Light-Harvesting 2 Complex During Remodeling of the Rhodobacter sphaeroides Intracytoplasmic Membrane Results in a Slowing of the Electron Transfer Turnover Rate of Photochemical Reaction Centers.
MedLine Citation:
PMID:  21366273     Owner:  NLM     Status:  Publisher    
ABSTRACT: A functional proteomic analysis of the intracytoplasmic membrane (ICM) development process was performed in Rhodobacter sphaeroides during adaptation from high intensity illumination to indirect diffuse light. This initiated an accelerated synthesis of the peripheral light-harvesting (LH2) complex relative to that of LH1-reaction center (RC) core particles. After 11 days, ICM vesicles (chromatophores) and membrane invagination sites were isolated by rate-zone sedimentation and subjected to clear native gel electrophoresis. Proteomic analysis of gel bands containing the RC-LH1 and LH2 complexes from digitonin-solubilized chromatophores revealed high levels of co-migrating electron transfer enzymes, transport proteins and membrane assembly factors relative to their equivalent gel bands from cells undergoing adaptation to direct low illumination. The GroEL chaperonin accounted for >65% of the spectral counts in the RC-LH1 band from membrane invagination sites, which together with the appearance of a universal stress protein suggested that the viability of these cells was challenged by light limitation. Functional aspects of the photosynthetic unit assembly process were monitored by near-IR fast repetition rate analysis of variable fluorescence arising from LH-bacteriochlorophyll a components. The quantum yield of the primary charge separation during the early stages of adaptation showed a gradual increase (variable/maximal fluorescence = 0.78 - 0.83 between 0 and 4 h, while the initial value of ~70 for the functional absorption cross-section (σ) gradually rose to 130 over four days. These dramatic σ increases showed a direct relation to gradual slowing of the RC electron transport turnover rate (tQA) from ~1.6 to 6.4 ms and an ~3- fold slowing of the rate of re-oxidation of the ubiquinone pool. These slowed rates are not due to changes in UQ pool size, suggesting that the relation between increasing σ and tQA reflects the imposition of constraints upon free diffusion of ubiquinone redox species between the RC and cytochrome bc1 complex as the membrane bilayer becomes densely packed with LH2 rings.
Kamil Woronowicz; Daniel Sha; Raoul N Frese; Robert A Niederman
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-3-2
Journal Detail:
Title:  Biochemistry     Volume:  -     ISSN:  1520-4995     ISO Abbreviation:  -     Publication Date:  2011 Mar 
Date Detail:
Created Date:  2011-3-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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