| Abstract
| - CO complexes formed in reduced nitric oxide reductase from Bacillus azotoformans were investigated with resonance Raman and FTIR techniques. These experiments shows the presence of two ν(C−O) bands, one at ∼1970 cm-1 assigned to the heme-CO complex, and one at ∼2070 cm-1 from the non-heme iron, FeBCO. At cryogenic temperatures, the heme-CO complex adopts a semi-bridging configuration with FeB which decreases its stretching frequency to ∼1910 cm-1 and decreases the ν(C−O) of FeBCO by ∼20 cm-1. The concomitant binding of two CO molecules, one per iron(II) at the active site, is consistent with the formation of a [{FeNO}7]2 iron-nitrosyl dimer during substrate turnover. This study strongly supports the notion that this family of enzymes utilizes a reaction mechanism based on catalysis by proximity, where the formation of two iron-nitrosyl groups promotes N−N bond formation.
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