General Description
White crystals.
Reactivity Profile
An amino acid. A 0.2M aqueous solution has a pH of 4.0., so acts as a weak acid. Has characteristics of both acid and base.
Air & Water Reactions
Water soluble.
Hazard
Use in fats restricted to 0.01%.
Fire Hazard
LOW. Ignites at very high temperatures.
Description
Glycine (abbreviated as Gly or G,56-40-6) is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its side-chain, glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG of the genetic code.
Glycine is a colourless, sweet-tasting crystalline solid. It is unique among the proteinogenic amino acids in that it is not chiral. It can fit into hydrophilic or hydrophobic environments, due to its minimal side chain of only one hydrogen atom. Glycine is also the genus name of the Soybean plant (species name = Glycine max).
Chemical Properties
A white, odorless, crystalline powder having a sweetish taste. Its
solution is acid to litmus. One g dissolves in about 4 mL of water.
It is very slightly soluble in alcohol and in ether. Glycine may be
prepared from chloroacetic acid and ammonia; from protein
sources, such as gelatin and silk fibroin; from ammonium bicarbonate
and sodium cyanide; by catalytic cleavage of serine; from
hydrobromic acid and methyleneaminoacetonitrile.
Chemical Properties
Glycine is odorless and has a slightly sweet taste.
Chemical Properties
Glycine occurs as a white, odorless, crystalline powder, and has a
sweet taste.
Chemical Properties
White or almost white, crystalline powder
Occurrence
Gelatin and silk fbroin are reportedly the best natural sources of this amino acid
Definition
ChEBI: The simplest (and the only achiral) proteinogenic amino acid, with a hydrogen atom as its side chain.
Preparation
From chloroacetic acid and ammonia; from protein sources, such as gelatin and silk fbroin; from ammonium bicarbonate and sodium cyanide; by catalytic cleavage of serine; from hydrobromic acid and methyleneaminoacetonitrile.
Production Methods
Glycine(56-40-6) was discovered in 1820, by Henri Braconnot who boiled gelatin with sulfuric acid.
Glycine is manufactured industrially by treating chloroacetic acid with ammonia :
ClCH2COOH + 2 NH3→H2NCH2COOH + NH4Cl
About 15 million kg are produced annually in this way.
In the USA (by GEO Specialty Chemicals, Inc.) and in Japan (by Shoadenko), glycine is produced via the Strecker amino acid synthesis.
Production Methods
Chemical synthesis is the most suitable method of preparation of
glycine. Amination of chloroacetic acid and the hydrolysis of
aminoacetonitrile are the favored methods of production.
Biosynthesis
Glycine(56-40-6) is not essential to the human diet, as it is biosynthesized in the body from the amino acid serine, which is in turn derived from 3-phospho glycerate. In most organisms, the enzyme Serine hydroxy methyl transferase catalyses this transformation via the cofactor pyridoxal phosphate :
serine + tetra hydro folate → glycine +N5,N10-Methylene tetrahydrofolate + H2O
In the liver of vertebrates, glycine synthesis is catalyzed by glycine synthase (also called glycine cleavage enzyme). This conversion is readily reversible : CO2 + NH4+ + N5,N10-Methylene tetra hydro folate + NADH + H+→ Glycine + tetrahydrofolate +NAD+
Glycine is coded by codons GGU, GGC, GGA and GGG. Most proteins incorporate only small quantities of glycine. A notable exception is collagen, which contains about 35 % glycine.
Biotechnological Production
Glycine(56-40-6) is manufactured exclusively by chemical synthesis, and two main processes
are practiced today. The direct amination of chloroacetic acid
with a large excess of ammonia gives good yields of glycine without producing
large amounts of di- and trialkylated products. This process is widely used in
China, where the main application of the glycine is as a raw material for the
herbicide glyphosate.
The other main process is the Strecker synthesis. The direct Strecker reaction of
formaldehyde and ammonium cyanide produces methylene amino acetonitrile,
which must be hydrolyzed in two stages to produce glycine . A more efficient
approach is to aminate the intermediate glycolonitrile, followed by hydrolysis].
An alternative method, which is more often applied for the homologous amino
acids, is the Bucherer–Bergs reaction. Reaction of formaldehyde and ammonium
carbonate or bicarbonate gives the intermediate hydantoin, which can be hydrolyzed
to glycine in a separate step.
Biological Functions
Glycine(56-40-6) is another inhibitory CNS neurotransmitter.
Whereas GABA is located primarily in the brain,
glycine is found predominantly in the ventral horn of
the spinal cord. Relatively few drugs are known to interact
with glycine; the best-known example is the convulsant
agent strychnine, which appears to be a relatively
specific antagonist of glycine.
Biological Functions
The principal function of glycine is as a precursor to proteins. It is also a building block to numerous natural products.
As a biosynthetic intermediate
In higher eukaryotes, D-Aminolevulinic acid, the key precursor to porphyrins, is biosynthesized from glycine and succinyl-CoA. Glycine provides the central C2N subunit of all purines.
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 potentia (IPSP). Strychnine is a strong antagonist at ionotropic glycine receptors, whereas bicuculline is a weak one. Glycine is a required coagonist 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), and it usually causes death by hyperexcitability. .
Agricultural Uses
Glycine is the simplest naturally occurring amino acid and is a constituent of most proteins. Its formula is H2N·CH2·COOH.
Pharmaceutical Applications
Glycine(56-40-6) is routinely used as a cofreeze-dried excipient in protein
formulations owing to its ability to form a strong, porous, and
elegant cake structure in the final lyophilized product. It is one
of the most frequently utilized excipients in freeze-dried injectable
formulations owing to its advantageous freeze-drying properties.
Glycine has been investigated as a disintegration accelerant in
fast-disintegrating formulations owing to its excellent wetting
nature.It is also used as a buffering agent and conditioner in
cosmetics.
Glycine may be used along with antacids in the treatment of
gastric hyperacidity, and it may also be included in aspirin
preparations to aid the reduction of gastric irritation.
Biological Activity
One of the major inhibitory neurotransmitters in the mammalian CNS, predominantly active in the spinal cord and brain stem. Also acts as a modulator of excitatory amino acid transmission mediated by NMDA receptors. Also available as part of the NMDA Receptor - Glycine Site Tocriset™ .
Biochem/physiol Actions
Glycine(56-40-6) has a pivotal role in lowering the plasma lipid levels in diabetic and obese patients by activating the CNS. During brain hypoxia glycine can stabilize the energetics disturbances in brain mitochondria. It also increases the in vitro development of porcine blastocysts when used along with glucose.
Safety
Glycine is used as a sweetener, buffering agent, and dietary
supplement. The pure form of glycine is moderately toxic by the
IV route and mildly toxic by ingestion.
Systemic absorption of glycine irrigation solutions can lead to
disturbances of fluid and electrolyte balance and cardiovascular and
pulmonary disorders.
LD50 (mouse, IP): 4.45 g/kg
LD50 (mouse, IV): 2.37 g/kg
LD50 (mouse, oral): 4.92 g/kg
LD50 (mouse, SC): 5.06 g/kg
LD50 (rat, IV): 2.6 g/kg
LD50 (rat, oral): 7.93 g/kg
LD50 (rat, SC): 5.2 g/kg
storage
Glycine starts to decompose at 233°C. Store in well-closed
containers. Glycine irrigation solutions (95–105% glycine) should
be stored in single dose containers, preferably type I or type II glass.
Purification Methods
Crystallise glycine from distilled water by dissolving at 90-95o, filtering, cooling to about -5o, and draining the crystals centrifugally. Alternatively, crystallise it from distilled water by addition of MeOH or EtOH (e.g. 50g dissolved in 100mL of warm water, and 400mL of MeOH is added). The crystals are washed with MeOH or EtOH, then with diethyl ether. Likely impurities are ammonium glycinate, iminodiacetic acid, nitrilotriacetic acid or/and ammonium chloride. [Greenstein & Winitz The Chemistry of the Amino Acids J. Wiley, Vol 3 p 1955 1961, Beilstein 4 IV 2349.]
Degradation
Glycine(56-40-6) is degraded via three pathways. The predominant pathway in animals and plants involves the glycine cleavage enzyme Glycine + tetra hydro folate + NAD+ → CO2 + NH4+ + N5,N10-Methylene tetra hydrofolate + NADH + H+ In the second pathway, glycine is degraded in two steps. The first step is the reverse of glycine biosynthesis from serine with serine hydroxymethyl transferase. Serine is then converted to pyruvate by serine dehydratase. In the third pathway of glycine degradation, glycine is converted to glyoxylate by D-amino acid oxidase. Glyoxylate is then oxidized by hepatic lactate dehydrogenase to oxalate in an NAD+-dependent reaction. The half-life of glycine and its elimination from the body varies significantly based on dose. In one study, the half-life was between 0.5 and 4.0 hours.
Presence in space
The detection of glycine in the interstellar medium has been debated . In 2008, the glycine - like molecule amino aceto nitrile was discovered in the Large Molecule Heimat, a giant gas cloud near the galactic center in the constellation Sagittarius by the Max Planck Institute for Radio Astronomy . In 2009, glycine sampled in 2004 from comet Wild 2 by the NASA spacecraft Stardust was confirmed, the first discovery of extraterrestrial glycine. That mission's results bolstered the theory of panspermia, which claims that the "seeds" of life are widespread throughout the universe.
Incompatibilities
Glycine may undergo Maillard reactions with amino acids to
produce yellowing or browning. Reducing sugars will also interact
with secondary amines to form an imine, but without any
accompanying yellow-brown discoloration.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (IM, IV, SC
injections; oral; rectal) and approved for irrigant solutions. Included
in parenteral (powders for injection; solutions for injection;
vaccines; kits for implant) and nonparenteral (orodispersible
tablets/oral lyophilizate; powders for inhalation; powders for oral
solution; tablets) formulations licensed in the UK.