Glycine (Gly)is an amino acid that has a single hydrogen atom as its side chain.
It is the simplest stable amino acid.
In solution or in the solid, glycine exists as the zwitterion.
Glycine is one of the proteinogenic amino acids.
Glycine is also an inhibitory neurotransmitter.
Interference with glycine its release within the spinal cord, such as occurs during a Clostridium tetani infection, can cause spastic paralysis due to uninhibited muscle contraction.
It is the only proteinogenic amino acid.
Glycine functions as a ligand for many metal ions, forming amino acid complexes.
Glycine condenses with itself to give peptides, beginning with the formation of glycylglycine:
Pyrolysis of glycine or glycylglycine gives 2,5-diketopiperazine, the cyclic diamide.
Glycine is not essential to the human diet, as it is biosynthesized in the body from the amino acid serine.
Serine is in turn derived from 3-phosphoglycerate.
In most organisms, the enzyme serine hydroxymethyltransferase catalyses this transformation via the cofactor pyridoxal phosphate:
In the liver glycine synthesis is catalyzed by glycine synthase.
Glycine can also be derived from threonine, choline or hydroxyproline via inter-organ metabolism of the liver and kidneys.
Glycine is degraded via three pathways. The predominant pathway is the reverse of the glycine synthase pathway.
The half-life of glycine and its elimination from the body varies significantly based on dose.
In one study, the half-life varied between 0.5 and 4.0 hours.
The principal function of glycine is it acts as a precursor to proteins.
Most proteins incorporate only small quantities of glycine.
Collagen, however contains about 35% glycine due to its periodically repeated role in the formation of collagen’s helix structure in conjunction with hydroxyproline.
δ-aminolevulinic acid, the key precursor to porphyrins, is biosynthesized from glycine and succinyl-CoA by the enzyme ALA synthase.
Glycine provides the central C2N subunit of all purines.[26]
Glycine is an inhibitory neurotransmitter in the central nervous system, especially in the spinal cord, brainstem, and retina.
With glycine receptors activation,chloride enters the neuron via ionotropic receptors, causing an inhibitory postsynaptic potential (IPSP).
Glycine is a required a a co-agonist along with glutamate for NMDA receptors.
In contrast to the inhibitory role of glycine in the spinal cord, this behavior is facilitated at the (NMDA) glutamatergic receptors which are excitator
Bile acids are normally conjugated to glycine in order to increase their solubility in water.
In the US, glycine is typically sold in two grades: United States Pharmacopeia (“USP”), and technical grade.
USP grade sales account for approximately 80 to 85 percent of the U.S. market for glycine.
Intravenous injections, a more expensive pharmaceutical grade glycine can be used.
Glycine is not widely used in foods for its nutritional value, except in infusions.
Glycine’s role in food chemistry is as a flavorant, being mildly sweet, and it counters the aftertaste of saccharine.
It also has preservative properties, perhaps owing to its complexation to metal ions.
The U.S. Food and Drug Administration no longer regards glycine and its salts as generally recognized as safe for use in human food, only permits food uses of glycine in certain conditions.
Glycine is an intermediate in the synthesis of a variety of chemical products.
Food sources of glycine.
Food Percentage content by weight (g/100g)
Snacks, pork skins 11.04 Sesame seeds flour (low fat) 3.43 Beverages, protein powder 2.37 Seeds, safflower seed meal, partially defatted 2.22 Meat, bison, beef and others ( 1.5–2.0 Gelatin desserts 1.96 Seeds, pumpkin and squash seed kernels 1.82 Turkey, all classes, back, meat and skin 1.79 Chicken, broilers or fryers, meat and skin 1.74 Pork, ground, 96% lean / 4% fat, cooked, crumbles 1.71 Bacon and beef sticks 1.64 Peanuts 1.63 Crustaceans, spiny lobster 1.59 Spices, mustard seed, ground 1.59 Salami 1.55 Nuts, butternuts, dried 1.51 Fish, salmon, pink, canned, drained solids 1.42 Almonds 1.42 Fish, mackerel 0.93 Cereals ready-to-eat, granola, homemade 0.81 Leeks, (bulb and lower-leaf portion), freeze-dried 0.7 Cheese, parmesan (and others), grated 0.56 Soybeans, green, cooked, boiled, drained, without salt 0.51 Bread, protein (includes gluten) 0.47 Egg, whole, cooked, fried 0.47 Beans, white, mature seeds, cooked, boiled, with salt 0.38 Lentils, mature seeds, cooked, boiled, with salt 0.37