Glycosyl-phosphatidylinositol-phospholipase type D: a possible candidate for the generation of second messengers

Membrane associated glycosyl-phosphatidylinositols have been shown to be the precursors of inositol phosphoglycan second messengers. Extraction of human liver membranes and purification by serial thin layer chromatography revealed three glycolipids which co-migrated with glycosyl-phosphatidylinositol from rat liver. These lipidic fractions were partially sensitive to treatment with nitrous acid and to hydrolysis by glycosyl-phosphatidylinositol-specific phospholipase D from bovine serum. In parallel, glycosyl-phosphatidylinositol isolated from rat liver was found to be a substrate for the enzyme generating a biologically active inositol phosphoglycan species (determined by measuring inhibition of protein kinase A activity and stimulation of cell proliferation within the chicken embryo cochleovestibular ganglion). This molecule was recognised by an anti-inositol phosphoglycan antibody. Hence, we propose that glycosyl-phosphatidylinositol-specific phospholipase D could be implicated in cellular signalling.