A water-soluble analogue of glucosaminylphosphatidylinositol distinguishestwo activities that palmitoylate inositol on GPI anchors

2-Palmitoylation of the inositol residue occurs during biosynthesis of glyc osylphosphatidylinositol (GPI) anchors, but the enzymology of this step has been enigmatic, With endogenously synthesized glucosamine-PI (GlcN-PI; a G PI intermediate), a CoA-dependent palmitoyl-CoA-independent acyl-transfer a ctivity (AT-1) has been reported in rodent preparations, In contrast, a pal mitoyl-CoA-dependent GlcN-PI acyltransferase activity (AT-2) was reported i n both rodent and yeast preparations with a novel water-soluble dioctanoyl GlcN-PI analogue, GlcN-PI(Cg), We report that AT-1, as well as AT-2, can be detected in rodent microsomes with GlcN-PI(C8), thus demonstrating the coe xistence of these activities in a single membrane preparation and the gener al utility of GlcN-PI(C8) for studying the GPI pathway, Unexpectedly, AT-2 was peripherally associated with microsomes, a property atypical for GPI bi osynthetic enzymes. (C) 2000 Academic Press.