The cell surface of Plasmodium gallinaceum sporozoites: microelectrophoretic and lectin-binding characteristics

The cell surface properties of Plasmodium gallinaceum sporozoites have been investigated by means of microelectrophoretic and lectin-binding studies. Their electrophoretic mobility has been measured as a function of pH, the results suggesting qualitative and quantitative differences in the surface ionogenic groups between sporozoites from mature oocysts and those from salivary glands. Reaction of sporozoites with citraconic anhydride produced a small but significant increase in mobility, whereas 5,5-dithio-bis-(2-nitrobenzoic) acid had no effect on mobility; thus there appear to be amino groups but not -SH groups at the surface of sporozoites. Treatment of sporozoites with trypsin considerably reduced their mobility and suggests that a significant proportion of the cell surface charge is associated with protein. Incubation with neuraminidase, however, had no effect on sporozoite mobility and indicates that sialic acid residues, responsible for much of the negative charge associated with mammalian cells, are probably not present on the cell surface of sporozoites. Evidence for the presence of carbohydrates on the cell surface membrane of sporozoites was sought using fluorescein isothiocyanate-Concanavalin A. Results demonstrated that ligands similar to alpha-D-glucose and alpha-D-mannose are not present in an exposed or reactive form on the cell surface membrane of P. gallinaceum sporozoites.