ISOLATION OF A GLYCOSYL-PHOSPHATIDYLINOSITOL (GPI) FROM RAT-BRAIN

BRAIN lipids were labelled with [1-C-14]-isethionyl acetimidate and pu rified by sequential thin layer chromatography. Four labelled peaks we re obtained, the first ones migrating with the same Rf as glycosyl-pho sphatidylinositol (GPI). Further proof of the isolation of GPI was obt ained by the observations that 44.8 % of the radioactivity associated with the lipid in peak I was converted to the water phase by the effec t of a PI-specific phospholipase C, and that the soluble material so o btained produced a dose-dependent inhibition of cAMP-dependent protein kinase activity. These findings indicate a biological equivalence bet ween GPI and its polar head group from rat brain and those described i n other cell types, and are consistent with the proposed role of these molecules in cellular signalling.