Cell-Cycle Specific Biosynthesis of the Photosynthetic Membrane of Rhodopseudomonas Sphaeroides: Structural Implications
Yen, Grace Shau-Ling
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https://hdl.handle.net/2142/71165
Description
Title
Cell-Cycle Specific Biosynthesis of the Photosynthetic Membrane of Rhodopseudomonas Sphaeroides: Structural Implications
Author(s)
Yen, Grace Shau-Ling
Issue Date
1983
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Abstract
Fusion of chromatophores, the photosynthetic membrane vesicle isolated from the intracytoplasmic membranes (ICM) of the photosynthetic bacterium Rhodopseudomonas sphaeroides, was achieved by the use of polyethylene glycol as fusogen. Ultracentrifugation, electron microscopy (EM), intrinsic density and isotope labeling were used to demonstrate chromatophore fusion. Except increased ion permeability, the orientation and integrity of fused chromatophores were demonstrated to be identical to control chromatophores by freeze-fracture EM, proteolytic enzyme digestion, enzymatic radioiodination, and transfer of chromatophore phospholipids mediated by phospholipid exchange protein extracted from R. sphaeroides.
Structural changes associated with the ICM during the cell cycle of R. sphaeroides have been studied by freeze-fracture EM. The isolated ICM vesicles, chromatophores, were fused in order to obtain large fracture faces. The density of the intramembrane particles (IMP) of the protoplasmic face (PF) of the ICM (from 50 to 83/10('4)nm('2)) was shown to be a linear function of the protein/phospholipid ratio (from 2.5 to 5.1, w/w) of the ICM. Under constant light intensity, both the average particle size and particle size distribution remained unchanged during the cell cycle. These results provide the structural basis for the earlier reported cell-cycle specific variations in both protein/phospholipid ratio and alteration in phospholipid structure of the ICM of R. sphaeroides during its photosynthetic mode of growth.
The average IMP diameter was 8.25, 9.08 and 9.75 nm at 4000, 500 and 30 ft-c, respectively. These results together with the increased frequency of larger particles, increased bacteriochlorophyll (Bchl) content at lower light intensities, and the unimodal distribution of particle size at different light intensities suggest that light harvesting Bchl-protein complexes are added randomly to new as well as pre-existing core particles. The lateral distribution of IMP were determined to be uniform in all samples.
When chromatophores were fused with small unilamellar liposomes, the IMP density decreased as input liposome phospholipid increased, whereas the average particle size remained constant and particle distribution became random in most cases.
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