Glutathione reductase
Encyclopedia
Glutathione reductase, also known as GSR or GR, is an enzyme
that reduces glutathione
disulfide (GSSG) to the sulfhydryl
form GSH
, which is an important cellular antioxidant
.
For every mole
of oxidized glutathione (GSSG), one mole of NADPH is required to reduce GSSG to GSH. The enzyme
forms a FAD
-bound homodimer. The glutathione reductase is conserved between all kingdoms
. In bacteria
, yeasts, and animal
s, one glutathione reductase gene is found; however, in plant
genomes, two GR genes are encoded. Drosophila
and Trypanosomes do not have any GR at all. In these organisms, glutathione reduction is performed by either the thioredoxin
or the trypanothione
system, respectively.
present in GSR to produce a transient FADH- anion. This anion then quickly breaks a disulfide bond (Cys58 - Cys63) and leads to Cys63's nucleophilically attacking the nearest sulfide unit in the GSSG molecule (promoted by His467), which creates a mixed disulfide bond (GS-Cys58) and a GS- anion. His467 of GSR then protonates the GS- anion to form the first GSH. Next, Cys63 nucleophilically attacks the sulfide of Cys58, releasing a GS- anion, which, in turn, picks up a solvent proton
and is released from the enzyme, thereby creating the second GSH. So, for every GSSG and NADPH, two reduced GSH molecules are gained, which can again act as antioxidants scavenging reactive oxygen species
in the cell
.
, like red blood cells, up to 10% of the glucose
consumption may be directed to the pentose phosphate pathway
(PPP) for production of the NADPH needed for this reaction. In the case of erythrocytes, if the PPP is non-functional, then the oxidative stress in the cell will lead to cell lysis
and anemia
.
. The activity can be monitored by the NADPH consumption, with absorbance at 340 nm, or the formed GSH can be visualized by Ellman's reagent
. Alternatively the activity can be measured using roGFP
(redox-sensitive Green Fluorescent Protein).
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that reduces glutathione
Glutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
disulfide (GSSG) to the sulfhydryl
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
form GSH
Glutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
, which is an important cellular antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
.
For every mole
Mole (unit)
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...
of oxidized glutathione (GSSG), one mole of NADPH is required to reduce GSSG to GSH. The enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
forms a FAD
FAD
In biochemistry, flavin adenine dinucleotide is a redox cofactor involved in several important reactions in metabolism. FAD can exist in two different redox states, which it converts between by accepting or donating electrons. The molecule consists of a riboflavin moiety bound to the phosphate...
-bound homodimer. The glutathione reductase is conserved between all kingdoms
Kingdom (biology)
In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...
. In bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, yeasts, and animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, one glutathione reductase gene is found; however, in plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
genomes, two GR genes are encoded. Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
and Trypanosomes do not have any GR at all. In these organisms, glutathione reduction is performed by either the thioredoxin
Thioredoxin
Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes. In humans, it is encoded by the TXN gene. Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the...
or the trypanothione
Trypanothione
Trypanothione is an unusual form of glutathione containing two molecules of glutathione joined by a spermidine linker. It is found in parasitic protozoa such as leishmania and trypanosomes. These protozoal parasites are the cause of leishmaniasis, sleeping sickness and Chagas' disease....
system, respectively.
Reaction mechanism of human glutathione reductase
NADPH reduces FADFAD
In biochemistry, flavin adenine dinucleotide is a redox cofactor involved in several important reactions in metabolism. FAD can exist in two different redox states, which it converts between by accepting or donating electrons. The molecule consists of a riboflavin moiety bound to the phosphate...
present in GSR to produce a transient FADH- anion. This anion then quickly breaks a disulfide bond (Cys58 - Cys63) and leads to Cys63's nucleophilically attacking the nearest sulfide unit in the GSSG molecule (promoted by His467), which creates a mixed disulfide bond (GS-Cys58) and a GS- anion. His467 of GSR then protonates the GS- anion to form the first GSH. Next, Cys63 nucleophilically attacks the sulfide of Cys58, releasing a GS- anion, which, in turn, picks up a solvent proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
and is released from the enzyme, thereby creating the second GSH. So, for every GSSG and NADPH, two reduced GSH molecules are gained, which can again act as antioxidants scavenging reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....
in the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
.
Glutathione reductase in human cells
In cells exposed to high levels of oxidative stressOxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
, like red blood cells, up to 10% of the glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
consumption may be directed to the pentose phosphate pathway
Pentose phosphate pathway
The pentose phosphate pathway is a process that generates NADPH and pentoses . There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars...
(PPP) for production of the NADPH needed for this reaction. In the case of erythrocytes, if the PPP is non-functional, then the oxidative stress in the cell will lead to cell lysis
Lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....
and anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
.
Monitoring glutathione reductase activity
The activity of glutathione reductase is used as indicator for oxidative stressOxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
. The activity can be monitored by the NADPH consumption, with absorbance at 340 nm, or the formed GSH can be visualized by Ellman's reagent
Ellman's reagent
Ellman's reagent is a chemical used to quantify the number or concentration of thiol groups in a sample.-Preparation:...
. Alternatively the activity can be measured using roGFP
RoGFP
The reduction-oxidation sensitive green fluorescent protein is a redox sensitive biosensor. Two cysteines were introduced into the beta barrel structure of the GFP, the oxidation state of the engineered thiols determines the fluorescence properties of the sensor...
(redox-sensitive Green Fluorescent Protein).