An Active Variant of Staphylococcal Nuclease Containing Norleucine in Place of Methionine

A methionine auxotroph of Staphylococcus aureus was grown with limiting methionine in the presence of a large excess of l-norleucine. Extracellular nuclease was produced that contained significant amounts of the latter amino acid. Treatment of such enzyme preparations with CNBr destroyed methionine-containing nuclease. The residual enzyme exhibited essentially normal activity, and it contained norleucine residues in place of the usual methionine residues.