What is Glutathione？
What is Glutathione？
Glutathione is a tripeptide antioxidant naturally produced in the body, and it plays a crucial role in safeguarding our proteins and DNA from damage caused by free radicals and oxidative stress. Beyond its physiological functions, this highly versatile molecule—and the proteins that interact with it—are widely used for various purposes in biotechnology research.
Structurally, glutathione is a tripeptide composed of glutamate, cysteine, and glycine. It is essential for maintaining cellular redox homeostasis and supporting detoxification pathways. In addition to these native roles, glutathione has several important applications in scientific research, including protein purification, protein refolding, and cell culture.
In this article, we will explore the cellular functions of glutathione, the different forms in which it exists, and its key applications in scientific research.
Figure 1. Structure of reduced glutathione (γ-L-Glu-L-Cys-Gly). The three amino-acid residues are color-coded: glutamate (pink), cysteine (orange), and glycine (green). The γ-peptide bond links the side-chain γ-carboxyl group of glutamate to the amino group of cysteine.
Why is glutathione so important?
Glutathione is absolutely essential for survival. Experimental studies have shown that mice lacking the ability to synthesize glutathione die before birth. Likewise, when glutathione production is switched off after birth, the animals die within about a month (Ashley, 2018). These findings underscore that glutathione is vital for both normal development and the maintenance of physiological balance in mammals.
So why is glutathione so crucial? You can think of glutathione as the cell’s internal pest control service. It captures and neutralizes small reactive molecules that would otherwise attack and damage the proteins and nucleic acids your cells depend on. These “pests” include oxidants and toxic metals. We will explore these harmful molecules in more detail in the next section, where we discuss how glutathione binds to and detoxifies them.
Glutathione is also a key cofactor for enzymes such as glutathione peroxidases and glutathione-S-transferases (Marí et al., 2009). A cofactor is a molecule that an enzyme needs in order to catalyze a chemical reaction. Unlike reactants, which are consumed, or products, which are formed during the reaction, cofactors emerge unchanged and can support the same reaction again and again. These glutathione-dependent enzymes likewise detoxify oxidizing molecules, so glutathione helps combat oxidants both directly and indirectly through enzyme catalysis.
Most healthy individuals synthesize sufficient glutathione on their own. However, certain patient groups—such as people with mutations in glutathione-synthesizing enzymes, as well as patients with AIDS or cystic fibrosis—may benefit from glutathione supplementation (Ashley, 2018).
We have now outlined many of glutathione’s major roles—but what exactly is glutathione at the molecular level?
The different forms of glutathione
Glutathione can exist in several related forms, and it’s useful to understand these differences because each form is preferred in different experimental applications.
The molecule shown in Figure 1 is reduced glutathione. In redox chemistry, you can think of the reduced state as the form in which a molecule holds on to its electrons, and the oxidized state as the form in which those electrons are instead shared in bonds with other atoms. For glutathione, this redox change centers on the sulfur atom of the cysteine residue: in the reduced form, the sulfur keeps its electrons in a free thiol group (–SH) rather than sharing them in a bond (Figure 2).
Figure 2. Reduced glutathione with the lone pair electrons on the sulfur atom shown as dots. This is the reduced form of glutathione because the sulfur atom is retaining these electrons instead of sharing them in a covalent bond with another atom.
The oxidized form, in contrast, is generated when the cysteine residue uses those electrons to form a covalent bond with another molecule. This is how glutathione interacts with oxidants and toxic metals. Accordingly, one biologically relevant oxidized form of cysteine occurs when it is bound to a metal ion or another cellular oxidant (Figure 3).
Figure 3. Oxidized glutathione bound to arsenic (purple), a human carcinogen (Rubino, 2015). By binding arsenic, glutathione helps neutralize it and facilitate its removal from cells before it can damage other biomolecules.
When we talk about the oxidized form of glutathione sold as a purified chemical, we are usually referring to the dimeric form, in which two glutathione molecules are linked through a bond between their cysteine sulfur atoms (Figure 4).
Figure 4. Oxidized glutathione in which one glutathione molecule is covalently linked to another.
This difference in form may sound subtle, but it is actually very important. For several of the applications described in the next section, it is critical to choose the appropriate form of glutathione—either reduced or oxidized.
The final form of glutathione we will mention is glutathione reduced ethyl ester. This derivative shows much more efficient cellular uptake than either of the two forms discussed above. Therefore, when adding glutathione to cultured cells or animals, glutathione reduced ethyl ester is typically the preferred option. Once inside the cell, endogenous enzymes rapidly convert glutathione reduced ethyl ester back into reduced glutathione (Levy et al., 1993).
Scientific applications of glutathione
Glutathione is employed in a wide range of scientific workflows, including:
(1) Protein purification
(2) Protein refolding
(3) Cell culture
Protein purification
Glutathione S-transferase (GST) is a commonly used solubility tag. In this strategy, GST is genetically fused to a protein of interest to generate a GST-fusion protein, which helps keep the target protein soluble and prevents it from precipitating.
Because GST specifically binds glutathione, this interaction is widely exploited for affinity purification. The GST-fusion protein is first captured on glutathione–agarose resin. After non-specific and contaminating proteins are washed away, reduced glutathione is added to elute the GST-fusion protein from the resin (Figure 5).
Protein refolding
Reducing agents are routinely included in protein purification buffers because they help prevent many proteins from forming non-native disulfide bonds and aggregating. Disulfide bonds are covalent linkages between the sulfur atoms of cysteine side chains, as illustrated for oxidized glutathione (Figure 4).
Common reducing reagents include TCEP, DTT, and βME. These are relatively strong reductants and are very effective at suppressing disulfide bond formation.
Glutathione, however, behaves as a somewhat gentler reducing agent—here is what that means. Glutathione is typically used when you want a protein to “sample” different possible disulfide bond arrangements so that it can settle into the most energetically favorable pattern of disulfide bonds (Lundström-Ljung & Holmgren, 1995).
For instance, during expression and purification of a recombinant protein, a disulfide bond may form that would not normally exist in the protein’s native environment. By adding a mixture of reduced and oxidized glutathione, the protein can explore multiple disulfide bond states and, if the native configuration is thermodynamically preferred, it should eventually adopt this “correct” disulfide pattern (Figure 5).
“Energetically favorable” here literally means that the state has a more negative Gibbs free energy, which generally corresponds to a more compact protein structure with more internal interactions, similar to the schematic protein shown on the right side of Figure 5. In this way, glutathione helps ensure that the purified protein adopts the proper conformation.
Figure 5. The protein on the left represents a kinetically trapped species that arises during heterologous expression: the first and second cysteine residues form a disulfide bond simply because they are the earliest to appear during translation. By treating the protein with a mixture of reduced and oxidized glutathione, this non-native disulfide can be reshuffled, allowing the protein to refold into the more compact and thermodynamically favorable state shown on the right, where the disulfide bond is now formed between the first and third cysteine residues.
Cell culture
Glutathione plays a key role in maintaining redox homeostasis in cultured cells and is already included in many standard cell culture media formulations (Ishii & Mann, 2014). In some experiments, however, it can be useful to supplement additional glutathione—for example, to add it to media that does not contain any, to raise its concentration in media that already includes glutathione, or to refresh older media in which glutathione may have gradually become oxidized.
As discussed above, glutathione reduced ethyl ester is the preferred form for cell culture, because it is taken up by cells much more efficiently than other forms (Levy et al., 1993).
Glutathione is more than just a small tripeptide—it is an essential tool for both living systems and laboratory research. Whether you are investigating redox biology, optimizing protein folding, or improving cell culture performance, having a solid grasp of glutathione will serve you well.
Related Products from Aladdin
Aladdin catalog | Product name | Grade & purity | CAS |
Glutathione Agarose Resin (GST tag) | BioReagent 50% v/v | _ | |
Glutathione Reduced(GSH Reduced) | Moligand™ BioReagent Plus ≥98% | 70-18-8 | |
Glutathione Reduced(GSH Reduced) | Moligand™ 10mM in Water | 70-18-8 | |
Glutathione Reduced(GSH Reduced) | Moligand™ ≥98% | 70-18-8 | |
Glutathione Reduced(GSH Reduced) | Moligand™ for cell culture ≥98% | 70-18-8 | |
Glutathione Reduced(GSH Reduced) | GMP PharmPure™ Ph.Eur. | 70-18-8 | |
L-Glutathione oxidized | BioReagent ≥98% | 27025-41-8 | |
L-Glutathione oxidized | High-purity | 27025-41-8 | |
L-Glutathione oxidized | ≥98% | 27025-41-8 | |
Glutathione reduced ethyl ester | ≥90% | 92614-59-0 | |
Glutathione reduced ethyl ester | Moligand™ 10 mM in DMSO | 92614-59-0 |
References
[1] Ashley RD. Ask the Doctors – What do glutathione supplements do? UCLA Health News. 2018 Jul 10.
[2] Marí M, Morales A, Colell A, García-Ruiz C, Fernández-Checa JC. Mitochondrial glutathione, a key survival antioxidant. Antioxid Redox Signal. 2009;11(11):2685–2700. doi:10.1089/ars.2009.2695.
[3] Rubino FM. Toxicity of glutathione-binding metals: a review of targets and mechanisms. Toxics. 2015;3(1):20–62. doi:10.3390/toxics3010020.
[4] Levy EJ, Anderson ME, Meister A. Transport of glutathione diethyl ester into human cells. Proc Natl Acad Sci U S A. 1993;90(19):9171–9175.
[5] Lundström-Ljung J, Holmgren A. Glutaredoxin accelerates glutathione-dependent folding of reduced ribonuclease A together with protein disulfide-isomerase. J Biol Chem. 1995;270(14):7822–7828.
[6] Ishii T, Mann GE. Redox status in mammalian cells and stem cells during culture in vitro: Critical roles of Nrf2 and cystine transporter activity in the maintenance of redox balance. Redox Biol. 2014;2:786–794.
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