Phospholipid Synthesis and Incorporation Into Membranes of Rhodopseudomonas Sphaeroides
Cain, Brian Dale
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Permalink
https://hdl.handle.net/2142/77670
Description
Title
Phospholipid Synthesis and Incorporation Into Membranes of Rhodopseudomonas Sphaeroides
Author(s)
Cain, Brian Dale
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
Language
eng
Abstract
This thesis represents the first comprehensive study of phospholipid biosynthesis as it relates to intracytoplasmic membrane (ICM) assembly in Phodopseudomonas sphaeroides. Description of the phospholipid biosynthetic pathway and demonstration of cell cycle specific intermembrane transfer of phospholipids extend our understanding of photosynthetic membrane assembly in R. sphaeroides.
In the course of these studies the novel phospholipid N-acylphosphatidylserine (NAPS) was discovered, purified and characterized. In R. sphaeroides, NAPS accumulates largely at the expense of phosphatidylethanolamine (PE) in response to the addition of Tris(hydroxymethyl)-aminomethane (Tris) to the growth medium. High concentrations of Tris (40 mM) in the medium resulted in NAPS becoming the predominant phospholipid species present in the cell. With the exception of NAPS, R. sphaeroides synthesizes phospholipids essentially as described in other eubacteria. NAPS is representative of a third previously unknown branch of phospholipid metabolism. Tris apparently alters the equilibrium of CDP-diglyceride utilization to favor formation of NAPS at the expense of phosphatidylserine and to a lesser degree phosphatidylglycerolphosphate syntheses. Coupling the NAPS synthesis data with the observation that PE may be a product of NAPS metabolism leads to the suggestion of a pathway accounting for the synthesis of phospholipids in R. sphaeroides.
Studies of the incorporation of phospholipids into the ICM are entirely supportive of the hypothesis of Lueking et al. (1978) that phospholipids are only inserted into the ICM just prior to cell division. Localization of the phospholipid biosynthetic enzymes to a cytoplasmic membrane (CM) enriched membrane fraction of photoheterotrophically grown R. sphaeroides identified the CM as the site of cellular phospholipid synthesis. In vivo kinetic studies demonstrated cell cycle specific transfer of phospholipids into the ICM. Therefore, it follows that cell cycle regulation of phospholipid transfer, and not de novo synthesis accounts for discontinuous incorporation of phospholipids into the ICM.
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