Purification and immunocytochemical localization of neuraminidase from Tritrichomonas foetus

Lysis of Tritrichomonas foetus with a solution of the non-ionic detergent Triton X-114 at 0 °C, followed by low-speed centrifugation, resulted in a detergent-insoluble pellet and a detergent-soluble supernatant. The supernatant was further fractionated by phase separation at 30 °C into a detergent-rich phase and an aqueous phase. Neuraminidase activity was mostly located in the detergent-insoluble pellet. When the parasites were incubated with bacterial phosphatidylinositol phospholipase C (PI–PLC) prior to detergent solubilization and phase separation neuraminidase activity was predominantly recovered in aqueous phase, rather than in the pellet and detergent phase. The molecular mass determined by gel permeation in high performance liquid chromatography (HPLC) and SDS–PAGE was 80000 Da. Indirect immunofluorescence microscopy using polyclonal antibodies raised in rabbits against the purified neuraminidase, indicated that the enzyme is exposed on the cell surface. Previous treatment of the cells with PI–PLC significantly reduced antibody binding. Incubation of cryo-sections with the antibodies followed by detection using gold-labelled anti-rabbit IgG confirmed the presence of neuraminidase in the plasma membrane enclosing the cell body and flagella and in the membrane of vesicles preferentially located at the peripheral region of the protozoan.