Role of a conserved glutamine residue in tuning the catalytic activity of Escherichia coli cytochrome c nitrite reductase

The glutamine at position 263 in Escherichia coli NrfA was mutated to understand the roles of the active site calcium ion and coordinating glutamine residue in nitrite reduction to ammonia by cytochrome c nitrite reductase. The findings provided insight into important function of unusual Q263-calcium ion pair to increase substrate affinity through its role in stabilization of a network of hydrogen bonded water molecules in the active site heme distal ligand.