ABSTRACT
Phosphatidylcholine (PC) is the major phospholipid found in eukaryotic membranes. In the unicellular eukaryote, the yeast Saccharomyces cerevisiae, PC accounts for approximately 40 to 50% of the total membrane phospholipids. The regulation of PC biosynthesis by the water-soluble phospholipid precursor choline was first demonstrated by Lester and co-workers. The regulation of the enzymes in the de novo biosynthetic route of PC synthesis by water-soluble phospholipid precursors is absolutely dependent upon inositol. The regulation of the de novo pathway for PC biosynthesis in S. cerevisiae is complex. Cytidylyltransferase-Diacylglycerol synthase is associated with the mitochondrial and microsomal fractions of S. cerevisiae. Phosphatidylinositol synthase is associated with the mitochondrial and microsomal fractions of S. cerevisiae. Inositol-1-phosphate synthase is associated with the cytosolic fraction of S. cerevisiae and has been purified 500-fold relative to the activity in cell extracts with yields of 20 to 40%.
