In vivo labeling of myelin lipids and proteolipid protein with [3H]myristate, [14C]linoleate,and [14C]linolenate

To investigate the incorporation of essential fatty acids into myelin components, 24-day-old rabbits were injected intracerebrally with ¹⁴C]linoleate, ¹⁴C]linolenate, or ³H]Myristate for comparison. Animals were killed 22 hr later and myelin was isolated. ³H]myristate labeled all myelin lipids including monogalactosyl diglyceride, with the exception of sulfatides. With¹⁴C-essential fatty acids, only glycerophospholipids were efficiently labeled and their specific activities were in the following decreasing orders: PC>PI>PE>PS with ¹⁴C]linoleate, and PE>PC>PI=PS with ¹⁴C]linolenate. Among myelin proteins, PLP and DM-20 were labeled with all 3 precursors. PLP was purified from myelin labeled with¹⁴C-essential fatty acids. The label was then cleaved from the protein by alkaline methanolysis and was identified as a dienoic (¹⁴C]linoleate) or a tetraenoic (¹⁴C]linolenate) fatty acid. MBP was not labeled with ³H]myristate, but was slightly labeled with both¹⁴C-essential fatty acids. The signification of the latter result is discussed.Abbreviations FA fatty acid(s) - HPTLC high-performance thin-layer chromatography - MBP myelin basic protein - PLP proteolipid protein - PC phosphatidylcholine - PE phosphatidylethanolamine and ethanolamine plasmalogens - PI phosphatidylinositol - PS phosphatidylserine - SDS sodium dodecylsulfate