The protozoan parasite Toxoplasma gondii possesses a triple
surface membrane called the pellicle. This is made of an outer
plasmalemma and an inner membrane complex lying under the plasmalemma.
Using a
high salt glycerol treatment
followed by sonication, we have obtained a partial dissociation of the
pellicle.
A plasmalemma-enriched fraction was
isolated on 0·7M sucrose. It was identified by immunodetection
of
the tachyzoite major surface antigens. Protein content,
resolved by SDS–PAGE, revealed that the surface protein SAG1 is the
major component of the plasmalemma. The
plasmalemma fraction is made of small vesicles (20–100 nm) which
possess
a low density (1·085–1·090 g/cm3 in
sucrose)
contrasting with other eukaryotic plasma membranes
(1·12–1·16 g/cm3).