The identity of the proximal ligand of its catalytic heme 1 center - lysine or histidine - may directly affect how efficiently pentaheme cytochrome c nitrite reductase catalyzes the six-electron reduction of nitrite (NO 2 − ) to ammonium (NH 4 + ) and may also alter substrate specificity. This reaction is part of the pathway of dissimilatory nitrate reduction to ammonium, which competes with denitrification and avoids the form...