Variant surface glycoprotein of Trypanosoma brucei brucei AnTat 1.1: influence of the isolation conditions upon the disulfide linked dimer/monomer ratio

1. Using the variant surface glycoprotein (VSG) isolation procedure described by Baltz et al. (1976] Ann. Immunol. (Inst. Pasteur) 127 C, 761-774) which involves suspension of the trypanosomes in a pH 5.5 buffer, the Antwerpen trypanozoon antigenic type (AnTat) 1.1 VSG is mainly obtained as a disulfide linked dimeric form with a trace amount of a monomeric form. 2. The use of a parasite suspension buffer at pH 7.0 results in a slight decrease of the VSG dimer/monomer ratio. 3. pH 5.5 and 7.0 supernatants of centrifuged parasite suspensions were submitted to kinetic incubations at different temperatures and pH, and we found conditions involving transformation of the AnTat 1.1 VSG dimer into the AnTat 1.1 VSG monomer (shifting the pH 5.5 supernatant to pH 7.0 and incubation at room temperature). 4. This transformation of the AnTat 1.1 VSG dimer into the AnTat 1.1 VSG monomer is activated by the addition of 1 mM reduced glutathione, and is inhibited by the addition of 1 mM oxidized glutathione or 0.1 mM N-ethylmaleimide or cadmium acetate.