Enzyme

1.8.1.7 - Glutathione-disulfide reductase

Alternative Name(s)
  • NADPH-glutathione reductase.
  • Glutathione reductase.
  • NADPH:oxidized-glutathione oxidoreductase.
  • GSH reductase.
  • Glutathione S-reductase.
  • GSSG reductase.
  • NADPH-GSSG reductase.
  • Glutathione reductase (NADPH).

Catalytic Activity

2 glutathione + NADP(+) = glutathione disulfide + H(+) + NADPH

Cofactors

FAD.

Reaction Mechanism

    The pyrimidine nucleotide-disulphide oxidoreductases are a family of proteins which transfer electrons from NAD(P)H via FAD to a redox-active disulphide bond in the enzyme active site, which then reduces the substrate.

    The structure of the ubiquitous enzyme glutathione reductase (EC 1.6.4.2), which helps protect cells from oxidative stress, is similar to trypanothione reductase (EC 1.6.4.8), lipoamide dehydrogenase (EC 1.8.1.4), higher eukaryotic thioredoxin reductase (EC 1.6.4.5) and mercuric reductase (1.16.1.1).

    Initially, the enzyme is in the oxidised state, with its redox active cysteines 58 and 63 forming a disulphide bond to each other. A hydride is transferred from NAD(P)H to FAD, a process facilitated by Glu201, Lys66 and Tyr197, as demonstrated by mutagenesis and structural studies. From there the electron makes an SN2 attack on the sulfur atom of Cys63, causing Cys58 to be displaced as thiolate. This residue is now ready to attack the substrate, which in all cases except mercuric reductase is another disulphide bond. His467 from the other subunit of the dimer has an essential role here, as shown by mutagenesis; first it seems to withdraw a proton from Cys58, activating the latter residue for a nucleophilic attack on the substrate. The proton is then poised to polarise the resulting Cys58-substrate mixed disulphide bond, making it vulnerable to attack from Cys63 to return the enzyme to its rest state. In addition to His467, another residue from the second subunit is found in the active site: Glu472 is shown to be essential by mutagenesis, and in structures is seen to orientate the catalytic Histidine.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    His P00390 511 2gh5 467
    Glu P00390 516 2gh5 472
    Tyr P00390 241 2gh5 197
    Cys P00390 102 2gh5 58
    Cys P00390 107 2gh5 63
    Lys P00390 110 2gh5 66
    Glu P00390 245 2gh5 201
    Step Components

    overall product formed, overall reactant used, proton transfer, enzyme-substrate complex formation, native state of cofactor regenerated, intermediate formation, bimolecular nucleophilic substitution, intermediate terminated, aromatic bimolecular nucleophilic addition, aromatic unimolecular elimination by the conjugate base, native state of enzyme regenerated, rate-determining step, cofactor used, intermediate collapse, hydride transfer, enzyme-substrate complex cleavage

    Step 1.

    NADP eliminates a hydride ion, which attacks the FAD cofactor with concomitant double bond rearrangement.

    Step 2.

    The FAD oxyanion collapses, initiating a nucleophilic attack on Cys63 in a substitution reaction that eliminates Cys58 from the disulfide bond.

    Step 3.

    The FAD cofactor eliminates Cys63 with concomitant deprotonation of the nitrogen to which the hydride was added.

    Step 4.

    His467B deprotonates Cys63A.

    Step 5.

    Cys58 initiates a nucleophilic attack on the disulfide bond of oxidised glutathione in a substitution reaction, eliminating glutathione with concomitant deprotonation of His467B.

    Step 6.

    Cys63 initiates a nucleophilic attack on Cys58 in a substitution reaction, eliminating glutathione with concomitant deprotonation of water.

    Products.

    The products of the reaction.

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Protein name Organism
Glutathione reductase Slime mold
Glutathione reductase, cytosolic Mouse-ear cress
Glutathione reductase, mitochondrial Caenorhabditis elegans
Glutathione reductase, chloroplastic/mitochondrial Garden pea
Glutathione reductase, chloroplastic Mouse-ear cress

Citations