Summary
The yield of the M-substance from undried whole streptococci is shown to be about 4 per cent, half of which is nucleic acid and half the type-specific M-protein.
The nucleic acid is shown to be in the free state and to be the principal, and in some cases the sole, contaminant. It accompanies the protein on precipitation with acid in salt-like combination. The M-protein is separated from the nucleic acid by half-saturation with neutral ammonium sulfate; several successive precipitations are required to reduce the phosphorus-content from 3.0 to 0.1 per cent or less. Some of the properties of the purified protein are described.
An interesting property of the M-protein is its considerable increase in solubility at elevated temperatures. The utilization of this property for purification is possible for the rare cases where considerable protein contamination accompanies the M-protein.
The M-proteins studied are from strains 1048 (untyped) and 1685 (type 3). Similar chemical properties have been found. In the precipitin-reaction with antiserum to whole streptococci the 1685 M-protein gives a strong cross-reaction with 1048 antiserum, the 1048 M-protein appears to give less cross-reaction with 1685 antisera. A quantitative study of the precipitation of these proteins with a 1048 antiserum was made.
Good absorption of protective antibodies from homologous streptococcal antisera is obtained with the 1048 M-protein. The preparation of 1685 M-protein studied was poor in this respect.
