|Molecular formula||C 2 H 5 NO 2|
colorless and odorless, crystalline solid
|External identifiers / databases|
|Molar mass||75.07 g mol −1|
1.161 g cm −3
Decomposition: 232-236 ° C
|pK s value||
easily soluble in water
|ΔH f 0||
−528.5 kJ / mol
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Glycine , abbreviated to Gly or G , (also glycine or glycocolla , from ancient Greek κόλλα kólla: glue, according to systematic chemical nomenclature aminoacetic acid or aminoethanoic acid), is the smallest and simplest α - amino acid and was first obtained in 1820 from gelatin, i.e. from collagen hydrolyzate . It belongs to the group of hydrophilic amino acids and is the only proteinogenic (or protein-forming) amino acid achiral and therefore not optically active .
Glycine is not essential, so it can be synthesized by the human organism itself and is an important component of almost all proteins and an important node in the metabolism.
The name is derived from the sweet taste of pure glycine ( Greek γλυκύς glykýs , German 'sweet' ).
Glycine is the first amino acid that was obtained by acidic digestion of proteins. The director of the Botanical Garden in Nancy, Henri Braconnot , succeeded in isolating glycine after purification by digesting animal glue with sulfuric acid . These were sweet-tasting crystals. Assuming a sugar, he called the substance “sucre de gélatine” ( gelatine is the main component of glutinous glue ), in English glue sugar, according to its origin . Soon afterwards the substance was renamed glycocolla (“sweet glue”) before Jöns Jakob Berzelius decided in 1848 that he would use the shorter name glycine from now on. The chemical structure was not correctly described until 1858 by the French chemist Auguste André Thomas Cahours .
As a partial reaction, this reaction played a special role in the hypothesis that organic molecules as “building blocks” for the first primitive organisms were created around 4 billion years ago from the simple inorganic compounds of the primordial atmosphere of the earth. A composition of water (H 2 O), methane (CH 4 ), ammonia (NH 3 ), hydrogen (H 2 ) and carbon monoxide (CO) as well as helium (He) and other noble gases was assumed for this primordial atmosphere (cf. → Miller -Urey experiment ).
Chemically, glycine can also be produced from monochloroacetic acid and ammonia:
Most of the glycine in the body is absorbed through food, but it can also be made from serine .
Glycine is mainly present as an "inner salt" or zwitterion , the formation of which can be explained by the fact that the proton of the acidic carboxy group migrates to the lone pair of electrons on the nitrogen atom of the basic amino group :
The zwitterion does not migrate in the electric field because it is uncharged as a whole. Strictly speaking, this is the case at the isoelectric point (at a certain pH value, here 5.97), at which the glycine also has its lowest solubility in water.
The following examples give an overview of the glycine content and each relate to 100 g of the food; the percentage of glycine in relation to the total protein is also given:
|Pork , raw||21 g||0.95 g||4.5%|
|Chicken breast fillet , raw||21 g||0.95 g||4.4%|
|Salmon , raw||20.5 g||0.95 g||4.7%|
|Gelatin powder , unsweetened||86 g||19 g||22.3%|
|Chicken egg||12.5 g||0.43 g||3.4%|
|Cow's milk , 3.7% fat||3.3 g||0.07 g||2.1%|
|Walnuts||15 g||0.82 g||5.4%|
|Pumpkin seeds||30 g||1.85 g||6.1%|
|Wholemeal wheat flour||14 g||0.55 g||4.0%|
|Wholemeal corn flour||7.0 g||0.28 g||4.1%|
|Rice , unpeeled||8.0 g||0.39 g||4.9%|
|Soybeans , dried||36.5 g||1.9 g||5.2%|
|Peas , dried||24.5 g||1.1 g||4.4%|
All of these foods contain almost exclusively chemically bound glycine as a protein component, but no free glycine.
The conversion of serine to glycine is used not only to generate glycine but also to convert tetrahydrofolic acid into N 5 -N 10 -methylene tetrahydrofolic acid (TH4), which is required, among other things, for the synthesis of thymine nucleotides ( DNA component).
Conversely, glycine can be used to synthesize serine by absorbing CH 3 from TH4, which is then available for protein synthesis, as the basic substance of choline or as pyruvate.
Glycine is also often required for the synthesis of other components of the genetic material ( purines ).
- Glycine + succinyl-CoA → 5-aminolevulinic acid → porphyrin synthesis to build up the heme.
- Glycine + guanodine group (from arginine ) → guanidinoacetate , which can then be used in creatinine synthesis .
- Glycine + Glu-Cys peptide bond → glutathionic acid
Oxalic acid , which is harmful to health, can also be formed from glycine as a by-product .
It is particularly common in collagen , the most common protein in animal organisms. Here it makes up a good third of all amino acids, because due to its small size it allows the collagen to be rolled up to form its triple helix structure .
Glycine acts in the central nervous system via the glycine receptor as an inhibitory neurotransmitter , i.e. as an inhibiting signal substance. The action takes place via the opening of ligand-controlled chloride channels and thus leads to an inhibitory postsynaptic potential (IPSP), which reduces the activity of the downstream nerve cell.
Glycine-releasing nerve cells (glycinergic neurons) are found mainly in the brain stem and spinal cord , in the latter they inhibit the activity of the motor neurons of the anterior horn , which leads to a reduction in the activity of the muscles innervated by these cells.
Strychnine , which acts as an antagonist and blocks the binding site of the glycine receptor, and tetanus toxin , which inhibits the release of glycine, reduce the effect of glycine. By blocking the glycine receptors or reducing the glycine level, the inhibition of motor neuron activity is reduced, so that life-threatening cramps can occur.
Glycine encephalopathy can result from abnormal accumulation of glycine .
Glycine is added to foods as a flavor enhancer .
Glycine is also a component of infusion solutions for parenteral nutrition.
In molecular biological and biochemical research, glycine is used in the form of a TRIS -Glycine buffer system for protein separation using SDS-PAGE ; the glycine ions act as secondary ions in the stacking gel.
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