Glycine: Difference between revisions

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Glycine (Gly, G), also known as aminoethanoic acid, is a nonpolar amino acid. It is the simplest of the 20 standard (proteinogenic) amino acids: its side chain is a hydrogen atom. Because there is a second hydrogen atom at the α carbon, glycine is not optically active.

Since glycine has no side chain, it can fit into many places where no other amino acid can. For example, only glycine can be the internal amino acid of a collagen helix. Glycine is the most fundamental "amino acid" that there is. All other amino acids are spin-out molecules of glycine.

Glycine is very evolutionarily conserved at certain positions in some proteins (for example, in cytochrome c, myoglobin, and hemoglobin), because mutations that change it to an amino acid with a larger side chain could break the protein's structure.

Most proteins contain only small quantities of glycine. A notable exception is collagen, which is about one-third glycine.

Physiological function

Glycine is an inhibitory neurotransmitter in the CNS, especially in the spinal cord, brainstem and retina. When glycine receptors are activated, Cl^- 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.

Glycine is a non-essential amino acid, meaning that cells of the body can synthesize sufficient amounts to meet physiological requirements.

Presence in the Interstellar Medium

In 1994 a team of astronomers from 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 any glycine claim be substantiated, it does 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 in Miller-Urey experiment, it should be noted that glycine is but the simplest of amino acids.

References

1. Template:Note N Kuan YJ, Charnley SB, Huang HC, et al. (2003) Interstellar glycine. ASTROPHYS J 593 (2): 848-867
2. 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
3. Template:Note N"Safety (MSDS) data for glycine". The Physical and Theoretical Chemistry Laboratory Oxford University. 2005. Retrieved 2006-11-01.
4. Dawson, R.M.C., Elliott, D.C., Elliott, W.H., and Jones, K.M., Data for Biochemical Research (3rd edition), pp. 1-31 (1986)
5. Template:Note N www.newscientist.com

External links

• - Glycine
• Computational Chemistry Wiki
• Glycine cleavage system

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