Abstract
This review is the first on the composition and metabolism of Paramecium lipids. This ciliated protozoa is a useful system for studying the structure and function of biomembranes since it can be grown under chemically defined culture conditions in large numbers; much is known about its genetics, membrane electrophysiology, and ultrastructure; and mutants with defective membrane functions are available which are reported to have lipid alterations. Pure preparation of the cell surface ciliary membrane are readily isolated. The organism and its ciliary membrane contain a variety of polar lipids, sterols, and steryl esters. The polar lipids include substantial amounts of ether lipids, sphingolipids, and phosphonolipids. the biosyntheses of fatty acids and specific moieties of complex lipids in this organism are beginning to be examined with promises of elucidating biosynthetic mechanisms that are more difficult to study in other organisms. More information on lipid metabolism is required to identify the bases for the defects in putative lipid/membrane mutants.
Highlights
This review is the first on the composition and metabolism of Pammcciwn lipids
The extrusion organelle, the trichocyst, is synthesized and assembled in the cytoplasm, moves to the cell surface, docks at predetermined sites at the cell surface where it attaches to the cell membrane, and the contents of the membrane-bound organelle are released upon fusion of trichocyst and cell surface membranes [21,22,23,24,25]
Changes in molecular bulky groups such as O H groups in SPL long chain bases and neutral sphingolipid fatty acids, and the lengths of aliphatic chains that affect hydrophobic interactions in the bilayer have not been sufficiently examined to determine their importance in maintaining membrane fluidity of the ciliary membrane or as possible thermosensory receptors [50]
Summary
The first ciliated protozoan that was found to require lipids for growth was Paramecium This organism requires a Cz4alkyl-substituted sterol with a double bond at the A5 or the A7 position, best fulfilled by stigmasterol or poriferasterol [33, 34]. In stationary and death phases, and in clonally aged cells, membrane-bound lipofuscin-like vesicles are present in the cytoplasm [41, 42] These vesicles have not been isolated and direct analyses of their contents have not been done. Phagocytotic rates (food vacuole formation) in 19 multimicronucleatum were highest at early culture ages [38] which could account for the rapid increase in lipids in lag phase cells. The rate of lipid uptake in 19 tetraurelia is not correlated with the rate of food vacuole formation, suggesting that bulk transport
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