The isolation by immunoabsorbent affinity chromatography and physicochemical characterization of Mycobacterium tuberculosis antigen 5.

Mycobacterium tuberculosis antigen 5 was purified from unheated culture filtrates by absorption onto an immunoabsorbent prepared with globulin from a monospecific goat antiserum and elution with 4.0 M urea at pH 9.0. The product was a homogeneous protein giving a single stainable band in acrylamide gel electrophoresis and a single precipitin arc in immunoelectrophoresis. It was found to have a molecular weight of 28,500 to 35,000 daltons and a sedimentation constant of 2.0. Amino acid analysis demonstrated it to be rich in aspartic acid, suggesting a cytoplasmic origin.