Glycine
- Glycine
- Glykoll
- Amino acetic acid
- Aminoethanoic acid
- Abbreviations: Gly ( three letter code )
- G ( single letter code )
B05CX03
Colorless, crystalline solid
Fixed
1.60 g · cm -3
Decomposition: 232-236 ° C
- PKCOOH: 2.34
- PKNH2: 9.60 ( each at 25 ° C)
- Readily soluble in water ( 249.9 g · kg -1 at 25 ° C; 391.0 g · kg -1 at 50 ° C; 543.9 g · kg -1 at 75 ° C; 671.7 g · kg -1 at 100 ° C)
-528.5 KJ / mol
Template: Infobox chemical / molecular formula search available
Glycine, abbreviated as Gly or G ( glycine or glycine also, AltGr κόλλα Kolla. Glue, by systematic chemical nomenclature or aminoethanoic acid amino acetic acid ) is the smallest and simplest α - amino acid and was first in 1820 of gelatin, ie, collagen hydrolyzate, obtained. It belongs to the group of hydrophilic amino acids and is the only proteinogenic (or protein building ) amino acid is not chiral and therefore not optically active.
Glycine is not essential, that can be manufactured by the human organism itself and is an important part of nearly all proteins and a major hub in metabolism.
The name is derived from the sweet taste of pure glycine ago ( gr γλυκύς: sweet).
Synthesis
That the reaction of formaldehyde, hydrogen cyanide and ammonia ( the Strecker synthesis ) resulting aminonitrile (more precisely, α - aminoacetonitrile ) provides for the hydrolysis of glycine:
This reaction assumes especial importance, by the hypothesis that the starting materials from the so-called primitive atmosphere could have formed that has surrounded the Earth about 4 billion years ago. They had a probably of hydrogen (H2), helium (He ), and to a lesser extent of methane ( CH4 ), ammonia ( NH3) and some other noble gases existing gas envelope.
Chemically glycine can also be made of monochloroacetic acid, and ammonia:
In the body the most glycine is ingested with food, but it can also be prepared from serine.
Properties
Glycine is present predominantly as the "inner salt " or zwitterion, whose formation can be explained by the fact that the proton of the acidic carboxyl group migrates to the lone pair of the nitrogen atom of the basic amino group:
In an electric field, the zwitterion migrates not because it is not loaded as a whole. Strictly speaking, this is at the isoelectric point ( at a given pH value, here 5.97 ) of the case in which the glycine has its lowest solubility in water.
- Van der Waals volume of 48
- Hydrophobicity: -0.4
Free glycine has a sweet taste, the detection threshold is 25 to 35 mmol / L.
Occurrence
The following examples provide an overview of Glycingehalte and are each based on 100 g of food, in addition, the percentage of glycine, based on the total protein, stated:
All of these foods contain almost exclusively chemically bound glycine as protein component, but no free glycine.
History
Glycine was first characterized by Braconnot 1820 as a protein constituent of glue. According to a different source, the first isolation of gelatin.
Functions
Metabolism
The conversion of serine to glycine is used in addition to the production of glycine and the reaction of tetrahydro folate to N5 -N10 -methylene- tetrahydrofolate ( TH4 ), inter alia, for the synthesis of thymine nucleotides ( DNA component ) is needed.
Conversely, serve from TH4 for the synthesis of serine, glycine with absorption of CH3, which is then available for protein synthesis, as the basic substance of choline or as pyruvate available.
Also for the synthesis of other components of the genetic material ( purines ) glycine is often needed.
It is also used in the biosynthesis of heme ( oxygen bond in the blood), creatine (storage ) in the muscle or glutathione:
Glycine succinyl -CoA → 5-aminolevulinic acid → porphyrin to the structure of the heme.
Glycine guano thing Ruppe ( from arginine ) → guanidinoacetate, which can then undergo in creatinine synthesis.
Glycine Glu- Cys peptide bond → Glutathionsäure
As a by- product can be formed from glycine poisonous oxalic acid.
As a so-called glucogenic or glucoplastische amino acid glycine can be implemented within the framework of metabolism via pyruvate to glucose.
Proteinaceous component
Due to its small size, glycine is preferentially incorporated into polypeptides on space matters ( the protein secondary structure).
Especially often it comes in the collagen, the most abundant protein in animal organisms,. This makes it good for one-third of all amino acids, as it allows the winding of collagen to its triple-helix structure due to its small size.
Nervous system
Glycine acts in the central nervous system via the glycine receptor as an inhibitory neurotransmitter, that is as an inhibitory signaling molecule. The action is carried out via the opening of ligand-gated chloride channels, and thus leads to an inhibitory postsynaptic potential ( IPSP ), which reduces the activity of the postsynaptic nerve cell.
At the NMDA receptor, however, it acts as a stimulant in addition to the Cardinal agonist glutamate at a specific glycine - binding site.
Glycine -releasing neurons ( glycinergic neurons ) occur mainly in the brain stem and spinal cord, in the latter, they inhibit the so-called motor neurons of the anterior horn, resulting in a reduction of muscle activity of the innervated by the cells of muscles.
A reduction in the effect Glycinwirkung strychnine, an antagonist of the glycine receptor, and the tetanus toxin which inhibits the release of glycine. The absence of inhibition increases muscle activity. This can lead to life-threatening convulsions.
Use
As a flavor enhancer glycine is added to foods.
Glycine and its sodium salt are generally approved in the EU as a food additive under the E number 640 with no maximum limit for food, adverse health effects are not known.
Glycine is further a component of infusion solutions for parenteral nutrition.
In the molecular biological and biochemical research glycine is used in the form of a tris -glycine buffer system in the protein separation by SDS- PAGE; the glycine ions function as a result of ions in the stacking gel.