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 Phot

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• 作者：Kamil Woronowicz ; Daniel Sha ; Raoul N. Frese ; Robert A. Niederman
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：June 7, 2011
• 年：2011
• 卷：50
• 期：22
• 页码：4819-4829
• 全文大小：978K
• 年卷期：v.50,no.22(June 7, 2011)
• ISSN：1520-4995

文摘

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 2 (LH2) complex relative to that of LH1鈭抮eaction 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鈭扡H1 and 鈭扡H2 complexes from digitonin-solubilized chromatophores revealed high levels of comigrating electron transfer enzymes, transport proteins, and membrane assembly factors relative to their equivalent gel bands from cells undergoing adaptation to direct low-level illumination. The GroEL chaperonin accounted for >65% of the spectral counts in the RC鈭扡H1 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鈭抌acteriochlorophyll 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鈭?.83 between 0 and 4 h), while the initial value of 70 for the functional absorption cross section (蟽) gradually increased to 130 over 4 days. These dramatic 蟽 increases showed a direct relation to gradual slowing of the RC electron transport turnover rate (蟿_QA) from 1.6 to 6.4 ms and an 3-fold slowing of the rate of reoxidation of the ubiquinone pool. These slowed rates are not due to changes in UQ pool size, suggesting that the relation between increasing 蟽 and 蟿_QA 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.