Complex sphingolipid synthesis in plants: characterization of inositolphosphorylceramide synthase activity in bean microsomes.

Complex glycophosphosphingolipids present in plants are composed of ceramide, inositolphosphate, and diverse polar oligosaccharide substituents. The activity of inositolphosphorylceramide (IPC) synthase (phosphatidylinositol:ceramide inositolphosphate transferase), the enzyme proposed to catalyze the initial committed step in the formation of these complex sphingolipids, was characterized in wax bean hypocotyl microsomes. Enzyme activity was assayed by monitoring the incorporation of fluorescent NBD-C(6) ceramide or [3H]inositolphosphate from radiolabeled phosphatidylinositol (PI) into product identified by TLC.