Generation of glycerophospholipid molecular species in the yeast Saccharomyces cerevisiae. Fatty acid pattern of phospholipid classes and selective acyl turnover at sn‐1 and sn‐2 positions

Abstract

Acyl chains linked to phospholipids of the yeast, Saccharomyces cerevisiae, are mainly C16:1 and C18:1 accompanied by minor amounts of C14:0, C16:0 and C18:0. In view of this rather simple fatty acid composition, the question arose whether in yeast, as in higher eukaryotes, fatty acyl groups were characteristically distributed among the sn-1 and sn-2 positions of distinct phospholipid classes. Analysis of fatty acids linked to the sn-1 and sn-2 positions of the major phospholipids showed that indeed saturated fatty acyl groups predominated in the sn-1 positions. While the percentage of saturated fatty acids was low (10%) in phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) from cells grown on rich medium, it was higher in phosphatidylserine (PtdSer) (25%) and highest in phosphatidylinositol (PtdIns) (41%). Oleate was mainly linked to position sn-2, while palmitoleate predominated in position sn-1. Striking differences in the fatty acid distribution of phospholipids that are metabolically closely related (e.g. PtdSer and PtdEtn, PtdEtn and PtdCho, and PtdIns and PtdSer) suggest that pathways must exist for the generation of distinct phospholipid molecular species within the different phospholipid classes. The highly selective incorporation of exogenous [14C]palmitic acid (90%) and [3H]oleic acid (99%) into the sn-2 position of PtdCho, and the preferential incorporation of these fatty acids into the sn-2 position of PtdEtn (70 and 90%, respectively, for palmitic and oleic acid) are compatible with the postulate that phospholipase A2-mediated deacylation followed by reacylation of the lysophospholipids is involved in the generation of phospholipid species in yeast.

Biochemistry, cell biology and molecular biology of lipids ofSaccharomyces cerevisiae

“…Distinct phospholipid molecules are produced, for example, by phospholipase A 2 -catalysed deacylation in the sn-2 position of existing phospholipids, followed by reacylation of the lysophospholipid with a coenzyme-A-activated fatty acid. Deacylation and reacylation of glycerophospholipids appear to be very efficient, 284 but cellular functions that depend on this energetically expensive process have yet to be identified.…”

Lipid-dependent Subcellular Relocalization of the Acyl Chain Desaturase in Yeast

“…Cells were then pulselabeled by the addition of 1 Ci [ 14 C]palmitic acid (NEN, Boston, MA) for 15 min at 30 or 37°C. Labeling was terminated by the addition of 10 mM NaN 3 , cells were broken with glass beads in a Merckenschlager homogenizer, and lipids were extracted and analyzed as previously described by Wagner and Paltauf (1994).…”

Characterization and Function in Vivo of Two Novel Phospholipases B/Lysophospholipases fromSaccharomyces cerevisiae

“…Preparation of Radioactively Labeled Phospholipid Substrates-Radioactively labeled phospholipids were prepared biosynthetically by incubating yeast cells with [1-14 C]palmitic acid (NEN Life Science Products) for 2 h, followed by extraction of lipids and isolation of phospholipid classes by thin-layer chromatography (16). Purity was typically Ͼ95%, as checked by TLC.…”

“…Purity was typically Ͼ95%, as checked by TLC. Radioactively labeled lyso-phospholipids were prepared from [1-14 C]palmitate-labeled phospholipids by hydrolysis with phospholipase A 2 from Naja naja (Sigma) and TLC separation (16). Phospholipid/Triton X-100 mixed micelles were prepared by combining phospholipid and detergent dissolved in chloroform/methanol (2:1, v/v), evaporation of the solvent under a stream of nitrogen, and subsequent dispersion in water (17).…”