Plasma membrane biogenesis in eukaryotic cells: translocation of newly synthesized lipid.

Abstract

We examined the transfer of sterols and phospholipids from their site of synthesis to the plasma membrane of Acanthamoeba castellanii. Cells were labeled with [3H]acetate, and plasma membrane fractions were isolated under conditions that minimize the nonspecific exchange of lipids between subcellular membrane fractions. Sterols and phospholipids were purified from both whole-cell homogenates and isolated plasma membrane. In whole cells, 3H-labeled lipids were formed, with no apparent time lag, in a linear manner up to 1 hr. Labeled sterol and phospholipids appeared in the plasma membrane, after a 30-min lag, at approximately the same rate. However, the ratio of newly synthesized sterol to phospholipid was significantly enriched in the plasma membrane relative to the whole cell, even at the earlier time points. Pulse-chase experiments indicated that sterols and phospholipids are turned over in the plasma membrane with similar, rather short half-lives. The results of these studies suggest that, although sterols and phospholipids are transported to the cell surface with similar kinetics, some sorting of the lipids must occur at an early stage in membrane biogenesis. The data are consistent with a model of lipid translocation by vesicular transport.

Cell Surface Polarity in Epithelia

“…Most lipids are known to be synthesized in the endoplasmic reticulum (ER), but how· they are moved from there has not yet been elucidated (Bell et al 1981, Pagano & Langmuir 1983. The newly synthesized lipids could move with the proteins by vesicular traffic from the ER over the Golgi complex to the cell surface (Dower et a11982, Pfenninger & Johnson 1983, Mills et al 1984, or by transfer through the aqueous, cytoplasmic phase, possibly by binding to lipid exchange proteins (Wirtz 1974, De Grella & Simoni 1982, Yaffe & Kennedy 1983, Sleight & Pagano 1983. No studies have yet been reported on lipid traffic in epithelial cells.…”

Targeting the Methyl Erythritol Phosphate (MEP) Pathway for Novel Antimalarial, Antibacterial and Herbicidal Drug Discovery: Inhibition of 1-Deoxy-D-Xylulose-5-Phosphate Reductoisomerase (DXR) Enzyme

“…1) [3][4][5]. These include functioning as modulators of membrane properties (prenyllipids in archaebacteria [6] and sterols in eubacteria and eukaryotes [7]), as carriers for electron transport (menaquinone, plastoquinone, phylloquinone and ubiquinone), [8] as light harvesting and photoprotecting pigments (carotenoids, phytol side chain of chlorophyll), as regulators of growth and development (steroid hormones, gibberellins, cytokinins, abscisic acid) [9] and in signal transduction (prenylated proteins) [10]. Isoprenoids also serve as attractants for pollinators and seed dispersers [11] and as antibiotics, and herbivore repellents as well as toxins in plants [12,13].…”

Lipid Traffic In Animal Cells

“…Some eukaryotes, like Acanthamoeba, do not contain SPH, but do enrich sterols in the plasma membrane (Dawidowicz 1987), probably during vesicle transport (Mills et al 1984). It is of possible evolutionary interest that cholesterol also displays a preference for disaturated PC, close to that for SPH (Lange et al 1979;see Phillips et al 1987): the mechanism of cis Golgi sorting may originally have used disaturated phospholipids.…”