From Wikipedia, the free encyclopedia
| Glycine[1] | |
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| IUPAC name | |
| Other names | Aminoethanoic acid |
| Identifiers | |
| Abbreviations | Gly, G |
| CAS number | [] |
| PubChem | |
| SMILES | |
| ChemSpider ID | |
| Properties | |
| Molecular formula | C2H5NO2 |
| Molar mass | 75.07 g mol−1 |
| Density | 1.1607 g/cm3 |
| Melting point |
233 °C (decomposition) |
| Solubility in water | 25 g/100 mL |
| Supplementary data page | |
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Structure and properties |
n, εr, etc. |
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Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
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Except where noted
otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Glycine (abbreviated as Gly or G)[2] is the organic compound with the formula NH2CH2COOH. It is the smallest of the 20 amino acids commonly found in proteins, coded by codons GGU, GGC, GGA and GGG. Glycine is unique among the proteinogenic amino acids in that it is not chiral. Most proteins incorporate only small quantities of glycine. A notable exception is collagen, which contains about 35% glycine.[3] Solid glycine is a colourless, sweet-tasting crystalline material.
[edit] Production
Glycine is manufactured industrially by treating chloroacetic acid with ammonia:[4]
- ClCH2COOH + 2 NH3 → H2NCH2COOH + NH4Cl
It is also produced via the Strecker amino acid synthesis.
[edit] Biosynthesis
Glycine is not essential to the human diet, since it is biosynthesized in the body from the amino acid serine, which is in turn derived from 3-phosphoglycerate. In most organisms, the enzyme Serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:[5]
- 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:[5]
- CO2 + NH4+ + N5,N10-Methylene tetrahydrofolate + NADH + H+ → Glycine + tetrahydrofolate + NAD+
[edit] Degradation
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:[6]
- 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.[6]
In the third pathway of glycine degradation, glycine is converted to glyoxylate by D-amino acid oxidase. Glycoxylate is then oxidized by hepatic lactate dehydrogenase to oxalate in an NAD+-dependent reaction.[6]
[edit] Physiological function
The principal function of glycine is as a precursor to proteins. It is also a building block to numerous natural products.
[edit] 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.[7]
[edit] 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 potential (IPSP). Strychnine is a strong antagonist at ionotropic glycine receptors, whereas bicuculline is a weak one. 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.[citation needed] The LD50 of glycine is 7930 mg/kg in rats (oral),[8] and it usually causes death by hyperexcitability.
[edit] Commercial uses
In the US, glycine is typically sold in two grades: United States Pharmacopeia (“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 use in 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.[9]
[edit] Animal and human foodstuffs
Other markets for USP grade glycine include its use an additive in pet food and animal feed. 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.