Purification and characterization of two protein antigens from the heterogeneous BCG85 complex in Mycobacterium bovis BCG.

The heterogeneous BCG85 complex is a major component of BCG culture fluid. BCG85A and BCG85B were purified by combining ammonium sulphate precipitation with chromatography on hydroxyapatite, DEAE-Sephacel and phenyl-Sepharose columns. Twenty percent of BCG85B was recovered. The chromatographic separation procedures were monitored by fused rocket immunoelectrophoresis. The BCG85 complex was found to consist of three antigens, which were heterogenous with regard to electrophoretic mobility, molecular weight (MW), hydrophobic and immunological properties. They were designated A, B and C in increasing order, according to their electrophoretic mobilities. Thus BCG85A had the lowest electrophoretic mobility, BCG85C the highest. The MW of BCG85A was found to be 31,000, while BCG85B had a slightly lower MW, 29,000, as determined by SDS-PAGE. The antigenic relationship between the components was evaluated by crossed immunoelectrophoresis and double diffusion, and reactions of partial identity between the antigens were found. The BCG85 complex occurs in far lower concentration in sonicates of BCG than in culture fluid.