Purification and characterization of a novel glycan-phosphatidylinositol-specific phospholipase C from <em>Trypanosoma brucei</em>

A novel membrane-bound glycan-phosphatidylinositol-specific phospholipase C, which catalyzes the conversion of membrane form variant surface glycoproteins to soluble variant surface glycoproteins, with the release of sn-1,2-dimyristylglycerol, has been isolated from Trypanosoma brucei. The activity was solubilized from trypanosome membrane fractions in nonionic detergent and purified by anion exchange chromatography on DEAE-cellulose followed by chromatography on phosphatidylinositol-Sepharose. The enzyme constitutes about 0.1% of the total cellular protein and has an apparent molecular weight of 39,800. The enzyme shows a head group specificity for molecules containing carbohydrate covalently linked to glycan-phosphatidylinositol, but can also act on the monoacyl derivative of membrane form variant surface glycoprotein. It shows no specific ion requirements but is stimulated by thiol-reducing agents and inhibited by ions that thiols chelate.