study on reaction of copper(II)-nitrito complexes with tridentate and tetradentate, with either O,O'-bidentate or O-unidentate modes of nitrite binding to the cupric center . Differing modes of nitrite coordination to the copper(II) ion lead to differing kinetic behavior
active site heme Fe(III) iron, the NrfA active site consists of a hexacoordinate high-spin heme with a lysine ligand on the proximal side and water/hydroxide or substrate on the distal side. There are four further highly conserved active site residues including a Q263 positioned near the heme iron for which the side chain, unusually, coordinates a conserved, essential calcium ion, overview
the NrfA active site consists of a hexacoordinate high-spin heme with a lysine ligand on the proximal side and water/hydroxide or substrate on the distal side. There are four further highly conserved active site residues including a Q263 positioned near the heme iron for which the side chain, unusually, coordinates a conserved, essential calcium ion, overview. An important function of the unusual Q263-calcium ion pair is to increase substrate affinity through its role in supporting a network of hydrogen bonded water molecules stabilizing the active site heme distal ligand
a conserved calcium ion (calcium I) with octahedral coordination is present near the active site. A second calcium site with octahedral geometry, coordinated to propionates of hemes 3 and 4, and caged by a loop non-existent in the previous structures. The main role of this calcium may not be electrostatic but structural
the highly conserved calcium located in the direct proximity of the active site plays an important role in the substrate conversion through the facilitation of the proton transfer steps
study on the reducing ability of the ferrous heme center, using two different tetraarylporphyrinate-iron(II) complexes, one with electron-donating paramethoxy peripheral substituents and the other with electron withdrawing 2,6-difluorophenyl substituents. The ferrous heme gives in all cases the reducing equivalent required to convert nitrite to nitric oxide, but the reduction ability of the heme center does not play a key role in the observed overall reaction rate
1.7.2.2 nitrite reductase (cytochrome; ammonia-forming)
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