The nature of the 4S antigens of the brucei subgroup trypanosomes

On isoelectric focusing of the supernatant fraction of trypanosome homogenate, the proteins were resolved into a large number of bands which were distributed within the pH range 4.0–8.6. A number of these bands, distributed within the pH range 5.5–6.0, was antigenic since it formed a precipitin line with antiserum on immunodiffusion analysis. This group, identified with the “4S” antigens, was found to be heterogeneous, consisting of at least seven components which differed in their isoelectric points, and hence in their net electric charges. They were, however, related because immunodiffusion analysis showed that they shared a common antigenic determinant. The components are protein-carbohydrate complexes because they stained for both proteins and carbohydrates. Absorption experiments showed that these components were the only protein-carbohydrate complexes in the supernatant. The presence of carbohydrates was further confirmed by the identification of two neutral sugars, d-mannose and d-galactose, in the acid hydrolysates of these antigens.