The Mechanism of Nitrite Reductase.

Area of Science:

• Biochemistry
• Enzymology
• Bioinorganic Chemistry

Background:

• Cytochrome c nitrite reductase (CcNiR) catalyzes nitrite activation and ammonia production.
• CcNiR utilizes a redox-active heme cofactor with lysine and arginine ligands, and four additional bis-histidine hemes for electron transfer.
• The precise mechanistic role of a nearby tyrosine residue has remained unclear.

Purpose of the Study:

• To elucidate the complex reaction mechanism of Cytochrome c nitrite reductase (CcNiR).
• To investigate the roles of specific amino acid residues and hemes in the catalytic cycle.
• To reconcile computational findings with experimental observations.

Main Methods:

• Computational modeling of enzyme mechanisms.
• Analysis of redox-active cofactors and ligand interactions.
• Comparison with previous experimental and computational studies.

Main Results:

• The tyrosine residue was found to be redox-active during the final ammonia production step.
• The arginine residue was observed to remain protonated throughout the entire catalytic mechanism.
• The proposed mechanism involves six reduction steps, differing from prior investigations.

Conclusions:

• The computational methodology employed accurately reproduces experimental findings for CcNiR.
• The study provides a refined mechanistic model for CcNiR, highlighting the roles of tyrosine and arginine.
• This work contributes to understanding complex enzymatic mechanisms, similar to previous studies on Photosystem II and Nitrogenase.