Evaluation of methods used to purify acid-extracted group A streptococcal M protein.

The literature includes descriptions of both acid-soluble and acid-insoluble M protein in the preparation of "hot acid-extracted group A streptococcal M protein." We present evidence for the contamination of crude type 1 acid-insoluble M protein. The purification of preparations of crude and partially purified acid-soluble type 1 and type 12 M protein is described. Our quantitative criteria for purification were recovery of M precipitin activity, improvement in specific activity, and removal of carbohydrate. Exclusion of nucleic acid is also discussed. Greater purification in a single passage was found with a carboxymethylcellulose column (with acidic elution) than with hydroxyapatite, diethylaminoethyl-Sephadex, or carboxymethyl-cellulose (with neutral elution) columns or with ammonium sulfate fractional precipitation. Carboxymethylcellulose with acidic elution was found to be a satisfactory standard laboratory procedure for the preparation of purified acid-extracted (acid-soluble) group A streptococcal M protein.