GLYCINE: FUNCTIONS, STRUCTURE AND PROPERTIES - NEUROPSYCHOLOGY - 2024

The glycine is one of the amino acids that form proteins of living things and also acts as a neurotransmitter. In the genetic code it is encoded as GGU, GGC, GGA or GGG. It is the smallest amino acid and the only non-essential of the 20 amino acids found within cells.

This substance also acts as a neurotransmitter, inhibiting the central nervous system. It acts in the spinal cord and brain stem, and contributes to the control of motor movements, the immune system, as a growth hormone and as a glycogen store, among others.

Glycine chemical structure

Glycine was first isolated from gelatin in 1820 by the director of the botanical garden in Nancy, Henri Braconnol, and performs multiple functions in the human body.

Structure and characteristics of glycine

Glycine molecular structure.

As can be seen in the image, glycine is composed of a central carbon atom, to which a carboxyl radical (COOH) and an amino radical (NH ₂) are attached. The other two radicals are hydrogen. It is therefore the only amino acid with two equal radicals; it has no optical isomerism.

Other of its properties are:

• Melting point: 235.85 ºC
• Molecular weight: 75.07 g / mol
• Density: 1.6 g / cm ³
• Global formula: C ₂ H ₅ NO ₂

Glycine is the simplest protein amino acid of all, which is why it is not considered one of the essential amino acids in the human body. In fact, the main difference between glycine and the other amino acids classified as essential, is that the body of people is capable of synthesizing it.

Glycine powder. Source: SPOTzillah CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0/)

In this way, it is not essential to incorporate this amino acid in the daily diet, since the body itself can produce glycine without having to ingest it.

To synthesize glycine, there are two different pathways, phosphorylated and non-phosphorylated, and the most important precursor is serine.

Thus, through an enzyme known as hydroxymethyl transferase, the body is able to transform serine into glycine.

Mechanism of action

Wisteria represented with sticks in 2D.

When the body synthesizes glycine from serine, the amino acid enters the bloodstream. Once in the blood, glycine begins to perform its functions throughout the body.

However, in order to do so, it needs to be coupled to a series of receptors widely distributed throughout different body regions. In fact, like all amino acids and other chemicals, when glycine travels through the blood, it does not perform any action by itself.

The actions are performed when it reaches specific parts of the body and is capable of attaching itself to the receptors found in those regions.

Glycine receptors

NMDA receptor present in the nervous system. 1. Cell membrane 2. Channel blocked by Mg2 + in the blocking site (3) 3. Site of blockade by Mg2 + 4. Binding site of hallucinogenic compounds 5. Binding site for Zn2 + 6. Binding site for agonists (glutamate) and / or antagonist ligands (APV) 7. Glycosylation sites 8. Proton binding sites 9. Glycine binding sites 10. Polyamine binding site 11. Extracellular space 12. Intracellular space 13. Complex subunit. Source: Blanca Piedrafita CC BY-SA 1.0 (http://creativecommons.org/licenses/by-sa/1.0/)

The glycine receptor is called the GLyR-like receptor, and is a specific type of receptor for glycine. When the amino acid binds to its receptor, currents are generated by the entry of chloride ions into the neuron.

Synaptic currents mediate inhibitory rapid responses that follow a rather complex time profile that we will not stop to discuss now.

Typically, the functioning of glycine with its receptor begins with a first phase of rapid response due to the impending opening of multiple chloride channels.

Subsequently, the response slows down due to inactivation and asynchronous closure of the channels.

Features

Glycine performs multiple functions in both the body and the brain of humans. Thus, despite not being one of the essential amino acids, it is highly important that the body contains high levels of glycine.

The discovery of the benefits provided by this substance and the problems that its deficit can cause is the main factor that has made glycine an element of great interest for nutrition.

As we will see below, the functions of glycine are many and very important. The main ones are:

Helps control ammonia levels in the brain

Ammonia is a chemical that most of us interpret as harmful and related to harsh chemicals.

However, ammonia itself is a byproduct of protein metabolism, so biochemical reactions in the body quickly convert to ammonia molecules.

In fact, the brain requires this substance to function properly and high or accumulated levels of ammonia in the brain can lead to pathologies such as liver disease.

Glycine thus ensures that this does not happen and controls the levels of ammonia in the brain regions.

Acts as a calming neurotransmitter in the brain

MRI of the brain

Glycine is an amino acid that when it accesses the brain performs neurotransmission functions, that is, it modulates the activity of neurons.

The main activity it performs in the brain is inhibition, which is why it is considered one of the main inhibitory neurotransmitters in the brain, along with GABA.

Unlike the latter (GABA), glycine acts in the spinal cord and brain stem.

The inhibition that it produces in these brain regions makes it possible to calm their functioning and modulate the hyperactivation of the brain.

In fact, glycine does not make a treatment for anxiety but it can be a particularly useful substance to prevent this type of psychological disturbance.

Helps control motor functions of the body

Another of the basic functions of glycine at the brain level is the control of the body's motor functions. Although dopamine is the substance most involved in this type of activity, glycine also plays an important role.

The activity of this amino acid, or rather, this neurotransmitter in the spinal cord, allows to control the movements of the extremities of the body.

Thus, glycine deficits are associated with movement control problems such as spasticity or sudden movements.

Acts as an antacid

Antacid is the name given to substances that act against heartburn. Thus, an antacid is responsible for alkalizing the stomach by increasing the pH and preventing the appearance of acidity.

The most popular antacids are sodium bicarbonate, calcium carbonate, magnesium hydroxide, and aluminum.

However, although to a lesser extent, glycine also performs this type of action, making it a natural antacid in the body itself.

Helps increase the release of growth hormone

Nervous system and brain

The growth hormone or GH hormone is a peptide substance that stimulates cell growth and reproduction.

Without the presence of this hormone, the body would be unable to regenerate and grow, so it would end up deteriorating. Likewise, deficits of this hormone can cause growth disorders in children and adults.

GH is a synthesized single chain 191 amino acid polypeptide, where glycine plays an important role.

Thus, glycine allows to promote the growth of the body, helps the creation of muscle tone and promotes strength and energy in the body.

Slows muscle degeneration

In the same way as the previous point, glycine also allows to slow muscle degeneration. The increase in growth, and the contribution of strength and energy that it originates in the body, not only translates into the construction of more vigorous muscle tissue.

Glycine promotes the reconstruction and regeneration of tissues at all times, so it collaborates in the construction of a healthy body.

In fact, glycine is an especially important amino acid for those who recover from surgery or suffer from other causes of immobility, since these create risk situations for muscle degeneration.

Improves glycogen storage

Glycogen is an energy reserve polysaccharide made up of branched chains of glucose. In other words, this substance makes all the energy that we have stored and that allows us to have reserves in the body.

Without glycogen, all the energy that we obtain through food would be poured into the blood immediately and would be spent on the actions we take.

In this way, being able to store glycogen in the body is an especially important factor for people's health.

Glycine, for its part, is a main amino acid of glycogen and collaborates in this storage process, so high levels of this substance allow increasing the efficiency of these functions.

Promotes a healthy prostate

The functions that glycine performs on the prostate of people is still in research phases and the data we have today is somewhat diffuse. However, glycine has been shown to present high amounts in prostate fluid.

This fact has motivated considerable interest in the benefits of glycine and today it is postulated that this amino acid could play a very important role in maintaining a healthy prostate.

Enhancement of sports performance

Taking L-arginine together with L-glycine has been shown to slightly increase the levels of stored creatine in the body.

Creatine combines with phosphates and is an important source of energy in power activities such as weight lifting.

Cognitive performance enhancement

Currently, the role that glycine can play in the cognitive functioning of people is also being investigated.

The increase in energy produced by this amino acid both physically and mentally is quite contrasted, so in the same way that it can increase physical performance, it is postulated that it can also increase cognitive performance.

In addition, its close relationship with neurotransmitters that carry out memory processes and cognitive capacity, such as acetylcholine or dopamine, makes it possible that glycine may be an important substance in intellectual performance.

In addition, a recent study has shown how glycine can reduce reaction time due to lack of sleep.

What can cause glycine deficiency?

Glycine is an amino acid that performs very important activities in different regions of the body; the lack of this substance can cause a series of alterations and pathological manifestations.

The most typical symptoms of glycine deficiency are:

1. Alterations in growth.
2. Sudden muscle contractions.
3. Exaggerated movements.
4. Delay in the restoration of damaged tissues.
5. Weakness of the prostate.
6. Weakness of the immune system.
7. Glucose disorders
8. Manifest brittleness in cartilage, bones and tendons.

Who can benefit the most from glycine?

Glycine performs multiple beneficial activities for the human body, which is why it is a positive amino acid for all people.

However, certain individuals, due to their health conditions, may require higher amounts of this substance, and may benefit more from it. These people are:

1. Individuals who suffer frequent infections.
2. People with frequent stomach acid problems.
3. Subjects with weaknesses in their immune system.
4. People who have problems in the regeneration of wounds or cuts.
5. Individuals prone to symptoms of anxiety or panic attacks, or characterized by very nervous behavior.

In these cases, it is especially important to incorporate glycine through the diet, consuming products rich in glycine such as meat, peas, cheese, nuts, mushrooms, spinach, eggs, cucumbers or carrots.

References

1. Fernandez-Sanchez, E.; Ten-War, FJ; Cubleos, B.; Gimenez, C. Y Zafra, F. (2008) Mechanisms of endoplasmic-reticulum export of glycine transporter-1 (GLYT1). Biochem. J. 409: 669-681.
2. Kuhse J, Betz H and Kirsch J: The inhibitory glycine receptor: Architecture, Synaptic localization and molecular pathology of a postsynaptic ion-channel complex. Curr Opin Neurobiol, 1995, 5: 318-323.
3. Martinez-Maza, R.; Poyatos, I.; López-Corcuera, B.; Gimenez, C.; Zafra, F. Y Aragón, C. (2001) The role of N-glycosylation in transport to the plasma membrane and sorting of the neuronal glycine transporter GLYT2. J. Biol. Chem. 276: 2168-2173.
4. Vandenberg, RJ; Shaddick, K. & Ju, P. (2007) Molecular basis for substrate discrimination by glycine transporters. J. Biol. Chem. 282: 14447-14453.
5. Steinert PM, Mack JW, Korge BP et al.: Glycine loops in proteins: Their occurrence in certain intermediate filament chains, loricrins and single-stranded RNA binding proteins. Int J Biol Macromol, 1991, 13: 130-139.
6. Yang W, Battineni ML and Brodsky B: Amino acid sequence environment modulates the disruption by osteogenesis imperfecta glycine substitutions in collagen-like peptide. Biochemistry, 1997, 36: 6930-6945.