Intracellular localization of the glycosyl-phosphatidylinositol-specific phospholipase C of Trypanosoma brucei.

Glycosyl-phosphatidylinositol-specific phospholipase C (GPI-PLC) is a membrane-bound enzyme of bloodstream forms of Trypanosoma brucei, which cleaves the GPI-membrane anchor of the variant surface glycoprotein forming diacylglycerol and 1,2-cyclic phosphate on the inositol ring. The cellular localization of the enzyme was studied by fractionation of sub-cellular organelles and immunofluorescence microscopy and was found to be primarily cytoplasmic. This was confirmed by immuno-electron microscopy using cryo-sections, which showed that the labelling was predominantly on the cytoplasmic side of intracellular membranes but was absent from the plasma membrane including the region lining the flagellar pocket. The significance of these results for the possible function of the phospholipase is discussed.