Trypanosoma brucei: release of variant surface glycoprotein during the parasite life cycle.

African trypanosome variant surface antigen, which was released from the Trypanosoma brucei parasite at two stages in its life cycle, has been characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of 4 M urea. Variant surface antigen released as exoantigen into the bloodstream of infected rats resembled the soluble form of the surface antigen. Variant surface antigen released from parasites undergoing transformation to the uncoated procyclic stage was detected as two molecular species: soluble variant surface antigen and a cleavage product of variant surface antigen. The data presented are consistent with enzymatic cleavage of the variant surface antigen C-terminal hydrophobic moiety operating to release parasite surface coat from living parasites.