Identification of an acid-lipase in human serum which is capable of solubilizing glycophosphatidylinositol-anchored proteins.

A lipase has been identified in human serum which can convert the membrane form of the variant surface glycoprotein of Trypanosoma brucei to a water soluble form. The conversion can be monitored by loss of [3H] myristic acid incorporated into the diacylglycerol of the glycophosphatidylinositol membrane anchor of the protein, but does not lead to the exposure of the antigenic determinant in the polar head group of the glycolipid. The serum lipase is a glycoprotein, and is optimally active at pH 5.4. Treatment at 62 degrees for one hour does not inactivate the enzyme, which is inhibited by chelating agents.