DmdNK was produced as described before. Briefly, it was expressed as a GST-fusion protein in Escherichia coli BL21 and purified using glutathione sepharose. The GST tag was cleaved off using thrombin and the enzyme was stored in aliquots at -20°C including 50 % glycerol, 1 % Triton X-100 and 1 mM dithiothreitol.