sentence: Examples of this strategy include the activation of the DNA cross ‐ linking pro ‐ drug CB1954 ( Figure 5 A ) 78 by wild ‐ type NTR with catalytic efficiency ( k / K ) in the range of 7 × 10 m s and the use of an engineered variant of the bacterial NTR for cell ‐ specific delivery of various small molecules in mammalian cells.79 Mutant NTRs can activate substrates such as CB1954 and nitrofurazone with up to 6 ‐ fold increase in catalytic efficiency ( k / K = 4.3 × 10 m s ) compared to wild ‐ type NTR .