The biosynthesis of phospholipids by human blood cells

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Abstract
The simultaneous incorporation in vitro of [P32]orthophosphate and [Me-C14]acetate into the phospholipids of human blood cells was measured. The doubly labeled phospholipids obtained after incubation with the radioactive isotopes for 6.5 hr. were fractionated by chromatography on silica gel, into ethanolamine -containing cephalins, serine-containing cephalins, phosphatidylcholine, sphingomyelin and other phospholipids. All fractions were labelled with both P32 and C14. Of the isolated phospholipid P32 the cephalins contained the most (67%), followed by the lecithins (12%) and the sphingomyelins (6.5%). The incorporation of C14 followed the same order, the cephalins containing 54%, the lecithins 11% and the sphingomyelins 10% of the isolated lipid C14. The fatty acids of the fractionated phospholipids were analysed by vapor-phase chromatography and different distributions of fatty acids for each fraction were observed. Two ethanolamine-containing phospholipid fractions were isolated. These differed in the rates of phosphate and acetate incorporation, and in fatty acid composition.