Further studies on the cell surface charge of Trypanosoma cruzi.

Trypanosoma cruzi has a negative surface which varies according to the ionic strength and the pH of the solution in which the cells are suspended. At low pH there is a decrease in the negative surface charge with an isoelectric point at pH 2.6 and 3.0 for epimastigote and trypomastigote forms, respectively. Below these pH values the cells have a positive surface charge. At higher pH there is an increase in the surface charge. Glutaraldehyde fixation did not interfere with the electrophoretic mobility (EPM) of the cells. Epimastigote and trypomastigote forms of T. cruzi have a characteristic EPM independent of the medium in which the cells were grown, the origin of the trypomastigotes or the strain of the parasite. Trypomastigotes have a higher negative surface charge than epimastigotes. Based on the change in the EPM of the cells treated with neuraminidase, is concluded that sialic acid is present on the cell surface of T. cruzi and that it is the main component responsible for the high negative surface charge of the trypomastigote form. Trypsin treatment also reduces the EPM of T. cruzi. Neuraminidase or trypsin-treated parasites recovered their normal EPM when incubated for 4 h in fresh culture medium. This process involves synthesis of protein since it is inhibited by puromycin.