Abstract
There are only minor changes in the amounts of the major lipid constituents of Dictyostelium discoideum plasma membranes during the early stages in the differentiation of this organism. By the time cells reach the pseudoplasmodial stage of development there are small increases in the amounts of phosphatidylinositol, phosphatidylglycerol, and lysophosphatidylethanolamine, and small decreases in the amounts of phosphatidylethanolamine and its plasmalogen form. There is also a slight decrease in the total amount of sterol in the plasma membrane during the transition from aggregation to pseudoplasmodium formation. However, no significant change in membrane fluidity as determined by electron paramagnetic resonance (EPR) accompanies these minor changes in lipid composition. It can be concluded that the establishment of cell-cell interaction in D. discoideum does not involve gross changes in plasma membrane fluidity or lipid composition. It was found that the plasmalogen form of phosphatidylethanolamine is a major phospholipid constituent in D. discoideum, and that this species is somewhat enriched in the plasma membrane.-Weeks, G., and F. G. Herring. The lipid composition and membrane fluidity of Dictyostelium discoideum plasma membranes at various stages during differentiation.
Highlights
M formation.,nosignificantchange in membrane fluidity as determined by electron paramagnetic resonance (EPR) accompanies these minor changes in lipid composition
Since theselatterstudies were on intact cells, changes in plasma membrane fluidity may have been masked by the incorporation of the fatty acid spin probe into internal membrane structures [19]
T h e strain was grown on Second, differentiation of some cell types is accom- HL5 medium as previously described [20] to a density panied by alterations in membrane fluidity [7,8,9,10]. of 5-7 x lo6 cells/ml
Summary
Supplementarykey words electron paramagnetic resonance spin probe . phospholipids . sterol fatty acid obtainedfromOxoidLtd. Since cell-cell contacts are essential for the differ- plasmodial (16 hr) cells, vegetative cells were washed entiationof Dictyosteliumdiscoideum butarenotrequired for growth, this organism is a convenient one Abbreviation: EPR, electron paramagnetic resonance. That conveniently separatedphosphatidylethanolaminefrom its plasmalogen form.The positions of theseparatedphospholipids were determined by iodinevapor treatment,andtheareascontaining lipid were scraped off and assayed for phospholipid content by the method of Bartlett [17], except that samples were digested in 70%perchloric acid for 45 min at 180°C. The aggregates or pseudoplasmodia were harvested from the plates and either analyzed directly for phospholipid composition or used for membrane preparation
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