1. Streptococcal proteinase is derived from an inactive precursor found in culture filtrates of proteinase-producing streptococci.

2. The precursor can be converted into the proteinase by low concentrations of trypsin but not by chymotrypsin.

3. In cultures grown in suitable media the conversion of precursor to proteinase is effected autocatalytically. This reaction occurs under reducing conditions and is initiated by active proteinase present in low concentrations with the precursor.

4. The autocatalytic reaction is suppressed or retarded by conditions which decrease the activity of the proteinase, e.g. by growing cultures at 22°C. instead of at 37°C. or by growing them under markedly aerobic conditions. It is also retarded in the presence of casein.

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