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Trimethylglycine
Trimethylglycine.png
Betaine-from-xtal-1999-3D-balls.png
IUPAC name
Other names Betaine, TMG, glycine betaine, betaine anhydrous, N,N,N-trimethylglycine
Identifiers
CAS number 107-43-7 Yes check.svgY
PubChem 247
MeSH Betaine
SMILES
ChemSpider ID 242
Properties
Molecular formula C5H11NO2
Molar mass 117.146
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Trimethylglycine (also commonly known as TMG), is an organic compound described by the formula (CH3)3N+CH2CO2H. Trimethylglycine was originally named betaine after its discovery in sugar beets (Beta vulgaris) in the 19th century. This small N-trimethylated amino acid exists as the zwitterion (CH3)3N+CH2CO2 - at neutral pH. This substance is often called ‘‘glycine betaine’’ to distinguish it from other betaines that are widely distributed in biology. Betaine hydrochloride is merely glycine betaine with a chloride counterion and is usually the first crystallised form obtained after extraction from beets. Glycine betaine is a byproduct of the sugar industry.

TMG is related to choline (trimethylaminoethanol), with the difference that the terminal carboxylic acid group of trimethylglycine has been reduced to a hydroxyl group in choline. The product of demethylation of TMG is dimethylglycine. Alkylated derivates of trimethylglycine have uses as quaternary ammonium zwitterionic surfactants.

Contents

Sources

Betaine is obtained by humans from foods, either as betaine or as choline-containing compounds. Food items with the highest content of betaine are wheat, spinach, shellfish, and sugar beets. Estimates of betaine intake are from 0.1 to 1 g/day and as high as 2.5 g/day for a diet high in whole wheat and seafood. Thus, the intake depends on food composition but is probably also related to production of the food items, including growing and osmotic conditions. Also, betaine is formed from choline.

The conversion of choline to betaine is a two-step enzymic process, which occurs in the liver and kidney. Choline is first oxidised to betaine aldehyde, a reaction catalysed by the mitochondrial choline oxidase (choline dehydrogenase, EC 1.1.99.1). In a subsequent step, betaine aldehyde is further oxidised in the mitochondria or cytoplasm to betaine by betaine aldehyde dehydrogenase (EC 1.1.1.8).

Functions

Betaine has three known functions in mammals: It is an organic osmolyte that accumulates in renal medullary cells and some other tissues to balance extracellular hypertonicity. Second, it acts as a chaperone to stabilise protein structure under denaturing conditions. Third, it serves as a methyl donor in the betaine homocysteine methyltransferase (BHMT) reaction, which converts homocysteine to methionine. Betaine is also present as an osmolyte in high concentrations (10s of millimolar) in many marine invertebrates, such as crustaceans and molluscs, and acts as a potent appetitive attractant to generalist carnivores such as the predatory sea-slug Pleurobranchaea californica[1].

Therapeutic uses

Anhydrous trimethylglycine (called Cystadane®) is approved by the FDA to treat homocystinuria, a disease caused by a birth defect in which homocysteine levels are too high.[2] Laboratory studies and two clinical trials have indicated that TMG is a potential treatment of nonalcoholic steatohepatitis.[3][4][5]

Many scientific papers have speculated on other potential uses for this substance, but none of these ideas have passed the drug approval process or been approved by the FDA. However, trimethylglycine (aka betaine) is available as a dietary supplement, and there is a great deal of confusing discussion on the internet about ways that this substance might be useful to "treat" certain diseases or conditions. As mentioned above, none of these uses have been approved by the FDA. Although betaine supplementation decreases the amount of adipose tissue in pigs, research in human subjects has shown no effect on body weight, body composition, or resting energy expenditure, calling into question its usefulness as a fat loss aid.[6]

In the veterinary/food production field, TMG is used by the ton in livestock farming, paired with lysine to increase "carcass yield", thereby helping increase muscle mass. It is also used in salmon farming, to relieve osmotic pressure in cells, as the animals make the switch from freshwater to saltwater.

Biochemical mechanisms

TMG functions very closely with choline, folic acid, vitamin B12, and S-adenosyl methionine SAMe. All of these compounds function as methyl donors. They carry and donate methyl functional groups to facilitate necessary chemical processes. The donation of methyl groups is important to proper liver function, cellular replication, and detoxification reactions. TMG also plays a role in the manufacture of carnitine and serves to protect the kidneys from damage.

Trimethylglycine/betaine donates a methyl group to convert homocysteine to methionine in a reaction catalysed by BHMT (Betaine Homocysteine Methyltransferase, E.C. 2.1.1.5, a zinc metalloenzyme). Methionine is then converted to SAMe by Methionine Adenosyl Transferase (MAT) using magnesium and adenosine triphosphate as co-factors.

Uses in molecular biology

Trimethylglycine can act as an adjuvant of the polymerase chain reaction (PCR) process, and of all other DNA polymerase-based assays such as DNA sequencing. By an unknown mechanism, it aids in the prevention of secondary structures in the DNA molecules, and prevents problems associated with the amplification and sequencing of GC-rich regions. Trimethylglycine makes guanosine and cytidine (strong binders) behave with thermodynamics similar to those of thymidine and adenosine (weak Binders). It has been determined under experiment that it is best used at a final concentration of 1M [7].

See also

References

  1. ^ Gillette R, Huang R-C, Hatcher N, Moroz LL (2000)Cost-benefit analysis potential in feeding behavior of a predatory snail by integration of hunger, taste and pain. Proc Natl Acad Sci USA 97: 3585-90 PMID: 10737805
  2. ^ Holm PI, Ueland PM, Vollset SE, Midttun O, Blom HJ, Keijzer MB, den Heijer M. (2005) Betaine and folate status as cooperative determinants of plasma homocysteine in humans. Arterioscler Thromb Vasc Biol. 379-85. PMID 15550695
  3. ^ Angulo P, Lindor KD (2001). "Treatment of nonalcoholic fatty liver: present and emerging therapies". Semin Liver Dis 21 (1): 81–88. doi:10.1055/s-2001-12931.  
  4. ^ Abdelmalek MF, Sanderson SO, Angulo P, et al. (December 2009). "Betaine for nonalcoholic fatty liver disease: results of a randomized placebo-controlled trial". Hepatology 50 (6): 1818–26. doi:10.1002/hep.23239. PMID 19824078.  
  5. ^ Miglio F, Rovati LC, Santoro A, Setnikar I (August 2000). "Efficacy and safety of oral betaine glucuronate in non-alcoholic steatohepatitis. A double-blind, randomized, parallel-group, placebo-controlled prospective clinical study". Arzneimittelforschung 50 (8): 722–7. PMID 10994156.  
  6. ^ Schwab U, Törrönen A, Toppinen L, et al. (November 2002). "Betaine supplementation decreases plasma homocysteine concentrations but does not affect body weight, body composition, or resting energy expenditure in human subjects". Am. J. Clin. Nutr. 76 (5): 961–7. PMID 12399266. http://www.ajcn.org/cgi/pmidlookup?view=long&pmid=12399266.  
  7. ^ Henke W, Herdel K, Jung K, Schnorr D, Loening SA (October 1997). [www.pubmed.com/9380524 "Betaine improves the PCR amplification of GC-rich DNA sequences."]. Nucleic Acids Res 25 (19): 3957–8. doi:10.1093/nar/25.19.3957. PMID 9380524. www.pubmed.com/9380524.  

External links








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