Phospholipase C-mediated release of neuraminidase from Tritrichomonas foetus cell surface

The release of the Tritrichomonas foetus plasma-membrane ectoenzyme neuraminidase by exogenous specific phospholipase C (PI-PLC) was investigated. Neuraminidase activity was determined using both the peanut agglutinin (PNA) hemagglutination test and the specific substrate N-acetylneuramin-lactose in a colorimetric assay. The release of the neuraminidase by PI-PLC was dependent on the reaction time and the concentration of PI-PLC. Neuraminidase activity was also detected in supernatant of untreated T. foetus. Spontaneous or PI-PLC-induced release of neuraminidase from protozoan cells was markedly decreased by 10 mM ZnCl2, suggesting the occurrence of an endogenous PI-PLC in the parasite. After T. foetus lysis at 37 degrees C with a solution of Triton X-114, neuraminidase activity was preferentially found in the aqueous phase rather than in the detergent phase, again suggesting that the parasite contains an endogenous PI-PLC that converts the hydrophobic form of neuraminidase anchored to the T. foetus cell membrane into a hydrophilic form. These results show that neuraminidase is linked to the T. foetus plasma membrane via a glycosylphosphatidylinositol anchor.