is an organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
COOH. Having a hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
substituent as its 'side chain', glycine is the smallest of the 20 amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s commonly found in protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s. Its codons are GGU, GGC, GGA, GGG cf. the genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
Glycine is a colourless, sweet-tasting crystalline solid. It is unique among the proteinogenic amino acid
Proteinogenic amino acids are those amino acids that can be found in proteins and require cellular machinery coded for in the genetic code of any organism for their isolated production. There are 22 standard amino acids, but only 21 are found in eukaryotes. Of the 22, 20 are directly encoded by...
s in that it is not chiral
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
. It can fit into hydrophilic
A hydrophile, from the Greek "water" and φιλια "love," is a molecule or other molecular entity that is attracted to, and tends to be dissolved by water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by, water and other polar substances...
In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
environments, due to its two hydrogen atom side chain.
Production and key properties
Glycine was discovered in 1820, by Henri Braconnot
Henri Braconnot was a French chemist and pharmacist.He was born in Commercy, his father being a counsel at the local parliament...
who boiled gelatin with sulfuric acid.
Glycine is manufactured industrially by treating chloroacetic acid
Chloroacetic acid, industrially known as monochloroacetic acid is the organochlorine compound with the formula ClCH2CO2H. This carboxylic acid is a useful building-block in organic synthesis.-Production:...
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
- 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
The Strecker amino acid synthesis, devised by Adolph Strecker, is a series of chemical reactions that synthesize an amino acid from an aldehyde . The aldehyde is condensed with ammonium chloride in the presence of potassium cyanide to form an α-aminonitrile, which is subsequently hydrolyzed to give...
There are two producers of glycine in the United States: Chattem Chemicals, Inc., a subsidiary of Mumbai-based Sun Pharmaceutical, and GEO Specialty Chemicals, Inc., which purchased the glycine and naphthalene sulfonate production facilities of Hampshire Chemical Corp, a subsidiary of Dow Chemical.
Chattem's manufacturing process ("MCA" process) occurs in batches and results in a finished product with some residual chloride but no sulfate, while GEO’s manufacturing process is considered a semi-batch process and results in a finished product with some residual sulfate but no chloride.
values are 2.35 and 9.78, so above pH 9.78, most of the glycine exists as the anionic amine, H2
. Below pH 2.35, its solutions contain mostly the cationic carboxylic acid H3
H. Its isoelectric point
The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....
(pI) is 6.06.
Glycine exists in zwitterionic form in solution. In this form, the partial charges on different atoms as determined using Gasteiger charge method are given as follows: N (+0.2358), H (attached to N) (+0.1964), alpha-C (+0.001853), H (attached to alpha-C) (+0.08799), carbonyl C (+0.085) and carbonyl O (-0.5445).
Glycine is not essential to the human diet, as it is biosynthesized in the body from the amino acid serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
, which is in turn derived from 3-phosphoglycerate. In most organisms, the enzyme Serine hydroxymethyltransferase
Serine hydroxymethyltransferase is an enzyme which plays an important role in cellular one-carbon pathways by catalyzing the reversible, simultaneous conversions of L-serine to glycine and tetrahydrofolate to 5,10-methylenetetrahydrofolate...
catalyses this transformation via the cofactor pyridoxal phosphate:
- serine + tetrahydrofolate → 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 tetrahydrofolate + 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
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
, which contains about 35% glycine.
Glycine is degraded via three pathways. The predominant pathway in animals involves the catalysis of glycine cleavage enzyme, the same enzyme also involved in the biosynthesis of glycine. The degradation pathway is the reverse of this synthetic pathway:
- Glycine + tetrahydrofolate + NAD+ → CO2 + NH4+ + N5,N10-Methylene tetrahydrofolate + 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
Serine Dehydratase or L-Serine Ammonia Lyase is in the ß-family of Pyridoxal Phosphate-dependent enzymes. SDH is found widely in nature, but its structural and chemical properties vary greatly among species. SDH is found in yeast, bacteria, and the cytoplasm of mammalian hepatocytes...
In the third pathway of glycine degradation, glycine is converted to glyoxylate by D-amino acid oxidase
D-amino acid oxidase is a peroxisomal enzyme containing FAD as cofactor that is expressed in a wide range of species from yeasts to human. It is not present in bacteria or in plants...
. Glyoxylate is then oxidized by hepatic lactate dehydrogenase
Lactate dehydrogenase is an enzyme present in a wide variety of organisms, including plants and animals.Lactate dehydrogenases exist in four distinct enzyme classes. Two of them are cytochrome c-dependent enzymes, each acting on either D-lactate or L-lactate...
Oxalate , is the dianion with formula C2O42− also written 22−. Either name is often used for derivatives, such as disodium oxalate, 2C2O42−, or an ester of oxalic acid Oxalate (IUPAC: ethanedioate), is the dianion with formula C2O42− also written (COO)22−. Either...
in an NAD+
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.
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
δ-Aminolevulinic acid is the first compound in the porphyrin synthesis pathway, the pathway that leads to heme in mammals and chlorophyll in plants....
, the key precursor to porphyrins, is biosynthesized from glycine and succinyl-CoA
Succinyl-Coenzyme A, abbreviated as Succinyl-CoA or SucCoA, is a combination of succinic acid and coenzyme A.-Source:It is an important intermediate in the citric acid cycle, where it is synthesized from α-Ketoglutarate by α-ketoglutarate dehydrogenase through decarboxylation...
. Glycine provides the central C2
N subunit of all purine
A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
As a neurotransmitter
Glycine is an inhibitory neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
in the central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
, especially in the spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
, brainstem, and retina. When glycine receptors are activated, chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
enters the neuron via ionotropic receptors, causing an Inhibitory postsynaptic potential
An inhibitory postsynaptic potential is a synaptic potential that decreases the chance that a future action potential will occur in a postsynaptic neuron or α-motoneuron...
Strychnine is a highly toxic , colorless crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine causes muscular convulsions and eventually death through asphyxia or sheer exhaustion...
is a strong antagonist at ionotropic glycine receptors, whereas bicuculline
Bicuculline is a light-sensitive competitive antagonist of GABAA receptors. It was originally identified in 1932 in plant alkaloid extracts and has been isolated from Dicentra cucullaria, Adlumia fungosa, Fumariaceae, and several Corydalis species. Since it blocks the inhibitory action of GABA...
is a weak one. Glycine is a required co-agonist along with glutamate for NMDA receptor
The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....
s. In contrast to the inhibitory role of glycine in the spinal cord, this behaviour is facilitated at the (NMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...
) glutaminergic receptors which are excitatory. The of glycine is 7930 mg/kg in rats (oral), and it usually causes death by hyperexcitability.
There is some evidence showing that 3000 milligrams of glycine before bedtime improves sleep quality.
In the US, glycine is typically sold in two grades: United States Pharmacopeia
The United States Pharmacopeia is the official pharmacopeia of the United States, published dually with the National Formulary as the USP-NF. The United States Pharmacopeial Convention is the nonprofit organization that owns the trademark and copyright to the USP-NF and publishes it every year...
(“USP”), and technical grade. Most glycine is manufactured as USP grade material for diverse uses. USP grade sales account for approximately 80 to 85 percent of the U.S. market for glycine.
- Pharmaceutical grade glycine is produced for some pharmaceutical applications, such as intravenous injections, where the customer’s purity requirements often exceed the minimum required under the USP grade designation. Pharmaceutical grade glycine is often produced to proprietary specifications and is typically sold at a premium over USP grade glycine.
- Technical grade glycine, which may or may not meet USP grade standards, is sold for use in industrial applications; e.g., as an agent in metal complexing and finishing. Technical grade glycine is typically sold at a discount to USP grade glycine.
Animal and human foods
Other markets for USP grade glycine include its use an additive in pet food
Pet food is plant or animal material intended for consumption by pets. Typically sold in pet stores and supermarkets, it is usually specific to the type of animal, such as dog food or cat food...
and animal feed
Compound feeds are feedstuffs that are blended from various raw materials and additives. These blends are formulated according to the specific requirements of the target animal...
. For humans, glycine is sold as a sweetener/taste enhancer. Food supplements and protein drinks contain glycine. Certain drug formulations include glycine to improve gastric absorption of the drug.
Cosmetics and miscellaneous applications
Glycine serves as a buffering agent
A buffering agent is a weak acid or base used to maintain the acidity of a solution at a chosen value. The function of a buffering agent is to prevent a rapid change in pH when acids or bases are added to the solution. Buffering agents have variable properties—some are more soluble than others;...
in antacids, analgesics, antiperspirants, cosmetics, and toiletries.
Many miscellaneous products use glycine or its derivatives, such as the production of rubber sponge products, fertilizers, metal complexants.
Glycine is an intermediate in the synthesis of a variety of chemical products. It is used in the manufacture of the herbicide glyphosate
. Glyphosate is a non-selective systemic herbicide used to kill weeds, especially perennials and broadcast or used in the cut-stump treatment as a forestry herbicide. Initially, glyphosate was sold only by Monsanto
The Monsanto Company is a US-based multinational agricultural biotechnology corporation. It is the world's leading producer of the herbicide glyphosate, marketed in the "Roundup" brand of herbicides, and in other brands...
under the tradename Roundup, but is no longer under patent.
Presence in space
The detection of glycine in the interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
has been debated. In 2008, the glycine-like molecule aminoacetonitrile
Aminoacetonitrile is a simple organic compound containing both nitrile and amino groups. It is somewhat similar to the simplest amino acid, glycine...
was discovered in the Large Molecule Heimat, a giant gas cloud near the galactic center in the constellation Sagittarius
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
by the Max Planck Institute for Radio Astronomy
The Max Planck Institute for Radio Astronomy is located in Bonn, Germany. It is one of 80 institutes in the Max Planck Society .-History:...
. In 2009, glycine sampled in 2004 from comet Wild 2 by the NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Stardust is a 300-kilogram robotic space probe launched by NASA on February 7, 1999 to study the asteroid 5535 Annefrank and collect samples from the coma of comet Wild 2. The primary mission was completed January 15, 2006, when the sample return capsule returned to Earth...
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.