Changes in the pattern of cell surface proteins during transformation of bloodstream forms of Trypanosoma brucei in vitro.

Transformation of coated bloodstream forms of Trypunosomu hrircei t o procyclic forms in vitro occurs over a period of 4-5 days 111, during which time the parasite changes its morphology and adapts its metabolism to life within the insect mid-gut [2,3]. One of the best characterized events during transformation is the loss o f the variable surface glycoprotein (VSG) that constitutes the dense surface coat of bloodstream forms of the parasite [4]. However, very little is known about the membrane proteins that are located beneath the VSG; for example, it is not clear whether these other 'masked' antigens are also shed during transformation or whether they remain on the surface of the procyclic forms. In this present report, we have used lactoperoxidasecatalysed radioiodination of the cell surface to label proteins that are located underneath the VSG of bloodstream forms and to follow the change in composition of the surface antigen population at various stages during transit through the transformation pathway.