In Vitro Studies on the Biosynthesis of the Surface Glycoprotein of Trypanosoma congolense1,2

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Abstract
Tritiated leucine, glucosamine, mannose and galactose were incorporated into the variant specific surface glycoprotein (VSG) of T. congolense in vitro. The uptake of the precursors is shown by sodium dodecylsulfate-polyacrylamide electrophoresis and fluorography, by assay of the radioactivity in immunoprecipitates obtained with specific antisera, and by the isolation of the labeled antigens by affinity chromatography on concanavalin A-sepharose and isoelectric focusing. The in vitro labeled VSG exhibits the same degree of microheterogeneity as that observed in the VSG isolated from trypanosomes grown in animals. Analysis of the incorporated sugars after hydrolysis of the glycoprotein showed that glucosamine and mannose were utilized in biosynthesis of the carbohydrate moiety directly; galactose was converted possibly to other intermediates before being incorporated into the antigen. Tunicamycin completely prevented the incorporation of the radiolabeled sugars into the surface glycoprotein. The unglycosylated VSG with a MW of 47 kDa [dalton] had completely lost its size heterogeneity.
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