Editing Active site (section)

===[[Glutathione reductase]]===
[[File:GSR Catalytic Cycle.PNG|thumb|the mechanism of glutathione reductase|400px]]

The role of [[glutathione]](GSH) is to remove accumulated reactive oxygen species which may damage cells. During this process, its [[thiol]] side chain is [[oxidation|oxidised]] and two glutathione molecules are connected by a [[disulphide bond]] to form a [[dimer (chemistry)|dimer]](GSSG). In order to regenerate glutathione the disulphide bond has to be broken, In human cells, this is done by [[glutathione reductase]](GR).{{citation needed|date=June 2024}}

Glutathione reductase is a dimer that contains two identical subunits. It requires one [[Nicotinamide adenine dinucleotide phosphate|NADP]] and one [[Flavin adenine dinucleotide|FAD]] as the [[cofactor (biochemistry)|cofactor]]s. The active site is located in the linkage between two subunits. The NADPH is involved in the generation of FADH-. In the active site, there are two [[cysteine]] residues besides the FAD cofactor and are used to break the disulphide bond during the catalytic reaction. NADPH is bound by three positively charged residues: Arg-218, His-219 and Arg-224.{{citation needed|date=June 2024}}

The catalytic process starts when the FAD is [[Organic redox reaction|reduced]] by NADPH to accept one electron and from FADH<sup>−</sup>. It then attacks the disulphide bond formed between 2 cysteine residues, forming one SH bond and a single S<sup>−</sup> group. This S<sup>−</sup> group will act as a nucleophile to attack the disulphide bond in the oxidised glutathione(GSSG), breaking it and forming a cysteine-SG complex. The first SG<sup>−</sup> anion is released and then receives one proton from adjacent SH group and from the first glutathione monomer. Next the adjacent S<sup>−</sup> group attack disulphide bond in cysteine-SG complex and release the second SG<sup>−</sup> anion. It receives one proton in solution and forms the second glutathione monomer.

<ref name=":0" />{{Rp|137–9}}