PHOSPHOLIPASE C-MEDIATED RELEASE OF NEURAMINIDASE FROM TRITRICHOMONAS-FETUS CELL-SURFACE

The release of the Tritrichomonas foetus plasma-membrane ectoenzyme ne uraminidase by exogenous specific phospholipase C (PI-PLC) was investi gated. Neuraminidase activity was determined using both the peanut agg lutinin (PNA) hemagglutination test and the specific substrate N-acety lneuramin-lactose in a colorimetric assay. The release of the neuramin idase by PI-PLC was dependent on the reaction time and the concentrati on of PI-PLC. Neuraminidase activity was also detected in supernatant of untreated T. foetus. Spontaneous or PI-PLC-induced release of neura minidase from protozoan cells was markedly decreased by 10 mM ZnCl2, s uggesting the occurrence of an endogenous PI-PLC in the parasite. Afte r T. foetus lysis at 37 degrees C with a solution of Triton X-114, neu raminidase activity was preferentially found in the aqueous phase rath er than in the detergent phase, again suggesting that the parasite con tains an endogenous PI-PLC that converts the hydrophobic form of neura minidase anchored to the T. foetus cell membrane into a hydrophilic fo rm. These results show that neuraminidase is linked to the T. foetus p lasma membrane via a glycosylphosphatidylinositol anchor.