Although to a smaller extent than NaRs, nitrite reductases have also been
explored for the construction of biosensing devices. NiRs are structurally diverse
enzymes that contain heme, copper, and Fe-S prosthetic groups [240, 241]. They
are organized into two groups: ammonia-forming (Eq. 11) and nitric oxide-forming
(Eq. 12) NiRs. Each group is further divided into two classes, according to the
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