Rational design of functional enzymes is a powerful strategy to gain deep insights into more complex native enzymes, such as nitric oxide reductase (NOR). Recently, we engineered a functional model of NOR by creating a two His and one Glu (2-His-1-Glu) non-heme iron center in sperm whale myoglobin (swMb L29E, F43H, H64, called FeBMb(-His)). It was found that FeBMb(-His) adopts a low-spin state with bis-His coordination in the absence of metal ions binding to the designed metal center. However, no structural information was available for the var...
