STREPTOCOCCAL NUCLEASES : I. FURTHER STUDIES ON THE A, B, AND C ENZYMES

Streptococcal DNAse C is more resistant to heat inactivation than the A or B enzyme. DNAses A and C are indifferent to the bacterial ribonucleic acid inhibitor whereas the B enzyme is markedly inhibited. Prolonged digestion with relatively large amounts of DNAse B results in chemical and biological destruction of the inhibitor. Ribonuclease as well as deoxyribonuclease activity is associated with the B enzyme. Both activities require divalent cations and both are inhibited by bacterial ribonucleic acid. The ratios of the two activities are constant in various preparations and after partial heat inactivation. Mutual inhibition of the two activities can be demonstrated in mixed substrate systems. The evidence presented is consistent with the view that the B enzyme is a single nuclease which can attack both deoxyribonucleic and ribonucleic acids.