Copper Based
To date, there have been several types of Copper Nitrite Reductases discovered. These CuNIR are found in many different plants and bacteria; for example, the bacterial genera Pseudomonas, Bordetella, Alcaligenes, and Achromobacter all contain CuNIR. What is common to all CuNIR is the presence of at least one type 1 copper center in the protein. These centers are similar to Azurin in their bonding structure. Each type 1 Cu is strongly bonded to a thiolate sulfur from a cysteine and to two imidazole nitrogens from different Histidines. This induces a distorted trigonal planar molecular geometry that is stabilized by two weaker interactions with a Methionine sulfur and a peptide oxygen.
The cysteine ligated to the type 1 Cu center is located directly next to a Histidine in the primary structure of the amino acids. This Histidine is bound to the Type 2 Cu center responsible for binding and reducing nitrite. This Cys-His bridge plays an important role in facilitating rapid electron transfer from the type 1 center to the type 2.
Read more about this topic: Nitrite Reductase
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