2-Mercaptoethanol

2-Mercaptoethanol (also β-mercaptoethanol, BME, 2BME, 2-ME or β-met) is the chemical compound with the formula HOCH₂CH₂SH. ME or βME, as it is commonly abbreviated, is used to reduce disulfide bonds and can act as a biological antioxidant by scavenging hydroxyl radicals (amongst others). It is widely used because the hydroxyl group confers solubility in water and lowers the volatility. Due to its diminished vapor pressure, its odor, while unpleasant, is less objectionable than related thiols.

Preparation

2-Mercaptoethanol may be prepared by the action of hydrogen sulfide on ethylene oxide:^[3]

Reactions

2-Mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes. This makes 2-mercaptoethanol useful as a protecting group.^[4]

Applications

Reducing proteins

Some proteins can be denatured by 2-mercaptoethanol, which cleaves the disulfide bonds that may form between thiol groups of cysteine residues. In the case of excess 2-mercaptoethanol, the following equilibrium is shifted to the right:

RS–SR + 2 HOCH₂CH₂SH ⇌ HOCH₂CH₂S–SCH₂CH₂OH + 2 RSH

By breaking the S-S bonds, both the tertiary structure and the quaternary structure of some proteins can be disrupted.^[5] Because of its ability to disrupt the structure of proteins, it was used in the analysis of proteins, for instance, to ensure that a protein solution contains monomeric protein molecules, instead of disulfide linked dimers or higher order oligomers. However, since 2-mercaptoethanol forms adducts with free cysteines and is somewhat more toxic, dithiothreitol (DTT) is generally more used especially in SDS-PAGE. DTT is also a more powerful reducing agent with a redox potential (at pH 7) of −0.33 V, compared to −0.26 V for 2-mercaptoethanol.^[6]

2-Mercaptoethanol is often used interchangeably with dithiothreitol (DTT) or the odorless tris(2-carboxyethyl)phosphine (TCEP) in biological applications.

Although 2-mercaptoethanol has a higher volatility than DTT, it is more stable: 2-mercaptoethanol's half-life is more than 100 hours at pH 6.5 and 4 hours at pH 8.5; DTT's half-life is 40 hours at pH 6.5 and 1.5 hours at pH 8.5.^[7]^[8]

Preventing protein oxidation

2-Mercaptoethanol and related reducing agents (e.g., DTT) are often included in enzymatic reactions to inhibit the oxidation of free sulfhydryl residues, and hence maintain protein activity. It is used in several enzyme assays as a standard buffer.^[9]

Denaturing ribonucleases

2-Mercaptoethanol is used in some RNA isolation procedures to eliminate ribonuclease released during cell lysis. Numerous disulfide bonds make ribonucleases very stable enzymes, so 2-mercaptoethanol is used to reduce these disulfide bonds and irreversibly denature the proteins. This prevents them from digesting the RNA during its extraction procedure.^[10]

Safety

2-Mercaptoethanol is considered toxic, causing irritation to the nasal passageways and respiratory tract upon inhalation, irritation to the skin, vomiting and stomach pain through ingestion, and potentially death if severe exposure occurs.^[11]

References

↑ Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 697. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. The prefixes ‘mercapto’ (–SH), and ‘hydroseleno’ or selenyl (–SeH), etc. are no longer recommended.
1 2 2-Mercaptoethanol
↑ Knight, J. J. (2004) "2-Mercaptoethanol" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette), J. Wiley & Sons, New York. doi:10.1002/047084289.
↑ "1,3-Dithiolanes, 1,3-Dithianes". Organic Chemistry Portal. Archived from the original on 17 May 2008. Retrieved 27 May 2008.
↑ "2-Mercaptoethanol". Chemicalland21.com. Archived from the original on 5 October 2006. Retrieved 8 October 2006.
↑ Aitken CE; Marshall RA, Puglisi JD (2008). "An oxygen scavenging system for improvement of dye stability in single-molecule fluorescence experiments". Biophys J. 94 (5): 1826–35. doi:10.1529/biophysj.107.117689. PMC 2242739. PMID 17921203.
↑ Yeh, J. I. (2009) "Additives and microcalorimetric approaches for optimization of crystallization" in Protein Crystallization, 2nd Edition (Ed: T. Bergfors), International University Line, La Jolla, CA. ISBN 978-0-9720774-4-6.
↑ Stevens R.; Stevens L.; Price N.C. (1983). "The Stabilities of Various Thiol Compounds used in Protein Purifications". Biochemical Education. 11 (2): 70. doi:10.1016/0307-4412(83)90048-1.
↑ Verduyn, C; Van Kleef, R; Frank, J; Schreuder, H; Van Dijken, J. P.; Scheffers, W. A. (1985). "Properties of the NAD(P)H-dependent xylose reductase from the xylose-fermenting yeast Pichia stipitis". The Biochemical Journal. 226 (3): 669–77. doi:10.1042/bj2260669. PMC 1144764. PMID 3921014.
↑ Nelson, David R.; Lehninger, Albert L; Cox, Michael (2005). Lehninger principles of biochemistry. New York: W.H. Freeman. p. 148. ISBN 0-7167-4339-6.
↑ "Material Safety Data Sheet". JT Baker. Retrieved 31 July 2011.

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