Methyl green

Methyl green (CI 42585) is a cationic or positive charged stain, related to Ethyl Green, that has been used for staining DNA since the 19th century.[1] It has been used for staining cell nuclei either as a part of the classical Unna-Pappenheim stain, or as a nuclear counterstain ever since.
In recent years, its fluorescent properties[2] when bound to DNA have positioned it useful for far-red imaging of live cell nuclei.[3] Fluorescent DNA staining is routinely used in cancer prognosis.[4] Methyl green also emerges as an alternative stain for DNA in agarose gels, fluorometric assays and flow cytometry.[3][5] It has also been shown that it can be used as an exclusion viability stain for cells. Its interaction with DNA has been shown to be non-intercalating, in other words not inserting itself into the DNA, but instead electrostatic with the DNA major groove.[6] It is used in combination with pyronin in the methyl green–pyronin stain which stains and differentiates DNA and RNA.

Methyl green
Identifiers
CAS Number
PubChem CID
UNII
CompTox Dashboard (EPA)
ECHA InfoCard100.001.316
Chemical and physical data
FormulaC27H35Cl2N3
Molar mass458.47

When excited at 244 or 388 nm in neutral aqueous solution, methyl green produces a fluorescent emission at 488 or 633 nm respectively. The presence or absence of DNA does not effect these fluorescence behaviors. When binding DNA under neutral aqueous conditions, methyl green also becomes fluorescent in the far red with an excitation maximum of 633 nm and an emission maximum of 677 nm.[3]

Commercial Methyl green preparations are often contaminated with Crystal violet. Crystal violet can be removed by chloroform extraction.[3]

References
  1. Carnoy JB (1884). La biologie cellulaire, étude comparée de la cellule dans les deux règnes / par le chanoine J.B. Carnoy... Bibliothèque nationale de France, département Sciences et techniques, 8-S-6259: J. Van In. p. 148. Retrieved 3 November 2017.CS1 maint: location (link)
  2. "fluorophores.org". www.fluorophores.tugraz.at. Retrieved 8 August 2016.
  3. Prieto D, Aparicio G, Morande PE, Zolessi FR (September 2014). "A fast, low cost, and highly efficient fluorescent DNA labeling method using methyl green". Histochemistry and Cell Biology. 142 (3): 335–45. doi:10.1007/s00418-014-1215-0. PMID 24671497. S2CID 11094194.
  4. Klonisch T, Wark L, Hombach-Klonisch S, Mai S (September 2010). "Nuclear imaging in three dimensions: a unique tool in cancer research". Annals of Anatomy = Anatomischer Anzeiger. 192 (5): 292–301. doi:10.1016/j.aanat.2010.07.007. PMID 20800459.
  5. Prieto D, Aparicio G, Machado M, Zolessi FR (May 2015). "Application of the DNA-specific stain methyl green in the fluorescent labeling of embryos". Journal of Visualized Experiments (99): e52769. doi:10.3791/52769. PMC 4542129. PMID 25993383.
  6. Kim SK, Nordén B (January 1993). "Methyl green. A DNA major-groove binding drug". FEBS Letters. 315 (1): 61–4. doi:10.1016/0014-5793(93)81133-K. PMID 8416812.


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