• Click the edit this page tab at the top. Save the page after each step, then edit it again.
• Click the 3D button (when editing, above the wikitext box) to insert Jmol.
• show the Scene authoring tools, create a molecular scene, and save it. Copy the green link into the page.
• Add a description of your scene. Use the buttons above the wikitext box for bold, italics, links, headlines, etc.

More help: Help:Editing

For more help, look at this link: http://www.proteopedia.org/wiki/index.php/Help:Getting_Started_in_Proteopedia

Nitrite Reductase

Overview

Nitrite reductase is an enzyme that belongs to the Oxidoreductase family for catalyzing the six-electron reduction of nitrite into ammonia, using the reduced ferredoxin as the electron donor. It is a monomeric protein with molecular mass near 66 kDa characterized by a unique which contains a single [4Fe–4S] cluster and a single siroheme (which serves as the binding site for nitrite) via a bridging sulfur atom from a cysteine residue. The protein has a globular fold consisting of 3 alpha/beta domains with the siroheme-iron sulfur cofactor at the interface of the three domains. The siroheme is surrounded by several ionizable amino acid residues that facilitate the binding and subsequent reduction of nitrite.

Nitrite reductase is found in several organisms and different forms that reduce nitrite to various products. The enzyme to the right contains a siroheme and iron-sulfur cluster to reduce nitrite to ammonia in certain plants. It is found in the stromal space of chloroplasts. Several other types of iron-based enzymes in bacteria reduce nitrite to nitrous oxide. There are also several types of Copper Nitrite Reductases found in many different plants and bacteria.

Mechanism

The electron flow proceeds initially from reduced ferredoxin to the enzyme's [4Fe–4S] cluster and subsequently from the reduced cluster to the siroheme. Since ferredoxin is a one-electron donor, the enzyme must accumulate six electrons in one-electron steps before it can reduce nitrite.

Structure

Secondary Structures

Nitrite Reductase has only one chain consisting of 591 residues. There are 33 (33% of chain) and 33 (21% of chain). The enzyme is composed of three .

Ligands

is an iron-containing, modified tetrapyrrole similar in structure to both heme and chlorophyll. It is a heme-like prosthetic group used by nitrite reductase to carry out the six-electron reduction of nitrogen. Nitrite is reduced to ammonia while still bound to siroheme. The siroheme-iron sulfur cofactor is at the interface of the three domains of the enzyme. The siroheme is surrounded by several ionizable amino acid residues that facilitate the binding and subsequent reduction of nitrite.

Has only one chain consisting of 591 residues. It consists of 33 helices (33% of chain) and 33 beta strands (21% of chain)

Ligand Binding to Active Sites

• binds Siroheme
• binds Iron-Sulfur Complex
• binds Potassium ion
• binds Chloride ion
• binds Chloride ion
• binds Nitrite