Glycine
  
| |
Glycine | |
| Systematic (IUPAC) name | |
| aminoethanoic acid | |
| Identifiers | |
| CAS number | 56-40-6 |
| PubChem | 750 |
| Chemical data | |
| Formula | C2H5NO2 |
| Mol. weight | 75.07 |
| SMILES | NCC(O)=O |
| Complete data | |
Glycine is the organic compound with the formula HO2CCH2NH2. It is one of the 20 amino acids commonly found in animal proteins. Its three letter code is gly, its one letter code is G, and its codons are GGU, GGC, GGA and GGG.[1] Because of its structural simplicity, this compact amino acid tends to be evolutionarily conserved in, for example, cytochrome c, myoglobin, and hemoglobin. Glycine is the unique amino acid that is not optically active. Most proteins contain only small quantities of glycine. A notable exception is collagen, which contains about one-third glycine.
Biosynthesis
Glycine is not essential to the human diet, since it is synthesized in the body. It is biosynthesized from the amino acid serine. The enzyme serine hydroxymethyl transferase catalyses this transformation:[2]
- HO2CCH(NH2)CH2OH + H2folate → HO2CCH2NH2 + CH2-folate + H2O
Physiological function
As a biosynthetic intermediate
Glycine is a building block to numerous species. Aminolevulinic acid, the key precursor to porphyrins is biosynthesized from glycine and succinoyl coenzyme A. Glycine provides the central C2N subunit of all purines.[2]
As a neurotransmitter
Glycine is an inhibitory neurotransmitter in the central nervous system, especially in the spinal cord, brainstem, and retina. When glycine receptors are activated, chloride enters the neuron via ionotropic receptors, causing an Inhibitory postsynaptic potential (IPSP). Strychnine is an antagonist at ionotropic glycine receptors. Glycine is a required co-agonist along with glutamate for NMDA receptors. In contrast to the inhibitory role of glycine in the spinal cord, this behaviour is facilitated at the (NMDA) glutaminergic receptors which are excitatory. The LD50 of glycine is 7930 mg/kg in rats (oral),Template:Ref N and it usually causes death by hyperexcitability.
Presence in the interstellar medium
In 1994 a team of astronomers at the University of Illinois, led by Lewis Snyder, claimed that they had found the glycine molecule in space. It turned out that, with further analysis, this claim could not be confirmed. Nine years later, in 2003, Yi-Jehng Kuan from National Taiwan Normal University and Steve Charnley claimed that they detected interstellar glycine toward three sources in the interstellar medium Template:Ref N. They claimed to have identified 27 spectral lines of glycine utilizing a radio telescope. According to computer simulations and lab-based experiments, glycine was probably formed when ices containing simple organic molecules were exposed to ultraviolet light Template:Ref N.
In October 2004, Snyder and collaborators reinvestigated the glycine claim in Kuan et al. (2003). In a rigorous attempt to confirm the detection, Snyder showed that glycine was not detected in any of the three claimed sources Template:Ref N.
Should the glycine claim be substantiated, the finding would not prove that life exists outside the Earth, but certainly makes that possibility more plausible by showing that amino acids can be formed in the interstellar medium. The finding would also indirectly support the idea of panspermia, the theory that life was brought to Earth from space. As the simplest of amino acids, it seems one of the most like to be detected in the interstellar medium.
ReferencesISBN links support NWE through referral fees
- Template:Note N Kuan YJ, Charnley SB, Huang HC, et al. (2003) Interstellar glycine. ASTROPHYS J 593 (2): 848-867
- Template:Note N Snyder LE, Lovas FJ, Hollis JM, et al. (2005) A rigorous attempt to verify interstellar glycine. ASTROPHYS J 619 (2): 914-930
- Template:Note NSafety (MSDS) data for glycine. The Physical and Theoretical Chemistry Laboratory Oxford University (2005). Retrieved 2006-11-01.
- Dawson, R.M.C., Elliott, D.C., Elliott, W.H., and Jones, K.M., Data for Biochemical Research (3rd edition), pp. 1-31 (1986)
- Template:Note N www.newscientist.com
External links
Template:ChemicalSources
| Major families of biochemicals | ||
| Peptides | Amino acids | Nucleic acids | Carbohydrates | Nucleotide sugars | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides | ||
| Analogues of nucleic acids: | The 20 Common Amino Acids | Analogues of nucleic acids: |
| Alanine (dp) | Arginine (dp) | Asparagine (dp) | Aspartic acid (dp) | Cysteine (dp) | Glutamic acid (dp) | Glutamine (dp) | Glycine (dp) | Histidine (dp) | Isoleucine (dp) | Leucine (dp) | Lysine (dp) | Methionine (dp) | Phenylalanine (dp) | Proline (dp) | Serine (dp) | Threonine (dp) | Tryptophan (dp) | Tyrosine (dp) | Valine (dp) | ||
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- ↑ IUPAC-IUBMB Joint Commission on Biochemical Nomenclature. Nomenclature and Symbolism for Amino Acids and Peptides. Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc. Retrieved 2007-05-17.
- ↑ 2.0 2.1 Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
