Proline: Definition, History, Etymology, Properties, Uses, Function and Benefits

It is an amino acid necessary for the production of collagen and cartilage.

It keeps muscles and joints flexible and helps reduce the sagging and wrinkles that accompany exposure to UV rays and normal skin aging.

Richard Willstätter synthesized Proline by the reaction of sodium salt of diethyl malonate with 1,3-dibromopropane in 1900. In 1901, Hermann Emil Fischer isolated Proline from casein and the decomposition products of the γ-phthalimido-propylmalonic ester.

The amino acid that improves the texture of the skin and helps the formation of collagen and helps contain the loss of collagen during aging.

Its molecule contains a secondary amino group (> NH) instead of the primary amino group (> NH2) characteristic of most amino acids.

Unlike other amino acids, Proline, first isolated from casein (1901), is easily soluble in alcohol. Collagen, the main protein in connective tissue, produces about 15 percent Proline.

It is one of several amino acids called non-essential; that is, animals can synthesize it from glutamic acid and do not require dietary sources.

Proline helps the body break down proteins for use in creating healthy cells in the body. It is absolutely essential for the development and maintenance of healthy skin and connective tissues, especially at the site of a traumatic tissue injury.

Proline and lysine (another amino acid that is important for protein synthesis) are necessary to produce hydroxyproline and hydroxylysine, two amino acids that form collagen. Collagen helps heal cartilage and cushion joints and vertebrae.

For this reason, supplementation with Proline may be beneficial for the treatment of conditions such as osteoarthritis , persistent soft tissue strains and chronic back pain.

The body needs Proline to maintain muscle tissue as well. Decreases in Proline levels have been observed in prolonged endurance runners and others after prolonged exercise.

Serious athletes who subject their body to routine and rigorous workouts may want to take a supplement containing Proline to avoid losing muscle mass: the body begins to sacrifice its muscle for energy when the glucose supply is low.

Proline is a non-essential amino acid. The body produces Proline from glutamic acid, and the deficiency is rare in healthy individuals with a healthy diet.

However, people who recover from a traumatic injury, particularly skin injuries such as severe burns, may want to supplement this amino acid.

People with pain caused by insufficient cartilage or collagen formation could also benefit from additional Proline in their diet.

Meat, dairy products and eggs are the best natural sources of Proline; Vegetarians or those on a low protein diet should seriously consider a combination amino acid supplement that contains, among other amino acids, Proline.

Proline supplements are available in separate capsules and tablets, but this amino acid is also often included in supplements marketed for the treatment of specific conditions.

For example, herpes (in combination with lysine), arthritis or back pain , or in supplements or sports, drinks marketed to bodybuilders and athletes.

Proline can be in supplements used to promote cardiovascular health, usually in combination with vitamin C.

The recommended therapeutic dose is between 500 milligrams and 1,000 milligrams daily, in combination with vitamin C. People with liver or kidney disease should not take this or any other amino acid supplement without first consulting their doctor.

Getting too much of an amino acid can unbalance the citric acid cycle, which makes the liver and kidneys work harder to eliminate toxins.

Proline (abbreviated as Pro or P, encoded by the CCU, CCC, CCA and CCG codons) is an amino acid that is used in protein biosynthesis.

It contains an α-amino group (found in the protonated form NH2 + under biological conditions), an α-carboxylic acid group (which is in the form of a deprotonated COO under biological conditions) and a side chain pyrrolidine, classifying it as an amino acid non-polar aliphatic (at physiological pH).

It is not essential in humans, which means that the body can synthesize it from the non-essential amino acid L-glutamate.

Proline is the only proteinogenic amino acid with a secondary amine, since the alpha-amino group binds directly to the side chain, so the α-carbon is a direct substituent of the side chain.

History and Etymology

Proline was isolated for the first time in 1900 by Richard Willstätter , who obtained the amino acid while studying N-methylProline. A year later, Emil Fischer published the synthesis of Proline from the propylmalonic ester of phthalimide. The name Proline comes from pyrrolidine, one of its components.

Proline was first isolated from casein in 1901 and, unlike any of the other amino acids, it is readily soluble in alcohol. It is a non-essential amino acid and can be synthesized from glutamic acid and does not require dietary sources.

Proline is one of the cyclic aliphatic amino acids that is a major component of the collagen protein, the structure of connective tissue that binds and is compatible with all other tissues.

Proline is synthesized from glutamic acid before its incorporation into procollagen during the translation of messenger RNA. After the pro-collagen protein is synthesized, it is converted by post-translational modification into hydroxyproline.

On a molar basis, Proline is incorporated into the protein at a rate of 4.2 percent with respect to other amino acids.

Proline improves the texture of the skin and helps the formation of collagen and helps to contain the loss of collagen during aging.

Collagen in the skin contains hydroxyProline and hydroxylysine, which is formed from Proline and lysine, in which ascorbic acid appears to be important in this conversion. The collagen contains about 15% Proline.

It is also believed to be important in maintaining muscles, joints and tendons.


Proline is derived biosynthetically from the amino acid L-glutamate. The glutamate-5-semialdehyde is first formed by glutamate 5-kinase (dependent on ATP) and glutamate-5-semialdehyde dehydrogenase (which requires NADH or NADPH).

This can spontaneously cyclize to form 1-pyrroline-5-carboxylic acid, which is reduced to Proline by pyrroline-5-carboxylate reductase (using NADH or NADPH), or converted to ornithine by ornithine aminotransferase, followed by cyclization by ornithine cyclodeaminase to form Proline.

Biological Activity

It has been found that L-Proline acts as a weak agonist of the glycine receptor and the ionotropic glutamate receptors NMDA and non-NMDA (AMPA / kainate). It has been proposed to be a potential endogenous excitotoxin.

In plants, the accumulation of Proline is a physiological response common to various stresses but is also part of the development program in generative tissues (eg, pollen).

Properties in Protein Structure

The characteristic cyclic structure of the Proline side chain provides Proline with exceptional conformational rigidity compared to other amino acids. It also affects the rate of formation of peptide bonds between Proline and other amino acids.

When Proline binds as an amide in a peptide bond, its nitrogen is not bound to any hydrogen, which means that it can not act as a hydrogen bond donor, but it can be a hydrogen bond acceptor.

The formation of peptide bonds with incoming Pro-tRNAPro is considerably slower than with any other tRNA, which is a general feature of N-alkylamino acids.

The formation of peptide bonds is also slow between an incoming tRNA and a chain ending in Proline, with the creation of slower Proline-Proline bonds of all.

The exceptional conformational rigidity of Proline affects the secondary structure of proteins close to a Proline residue and may explain the higher prevalence of Proline in the proteins of thermophilic organisms.

The secondary structure of the protein can be described in terms of the dihedral angles φ, ψ and ω of the protein backbone. The cyclic structure of the Proline side chain blocks the angle φ to approximately -65 °.

Proline acts as a structural disruptor in the middle of elements of regular secondary structures such as alpha helices and beta sheets, however, Proline is commonly found as the first residue of an alpha helix and also in the edge strands of beta sheets .

Proline is also commonly found in turns (another type of secondary structure) and helps in the formation of beta turns. This may explain the curious fact that Proline is usually exposed to solvents, despite having a completely aliphatic side chain.

Multiple Prolines and / or hydroxyProlins in a row can create a polyProline helix, the predominant secondary structure in collagen.

Hydroxylation of Proline by prolyl hydroxylase (or other additions of substituents that withdraw electrons such as fluorine) significantly increases the conformational stability of collagen.

Therefore, the hydroxylation of Proline is a critical biochemical process to maintain the connective tissue of higher organisms.

Serious diseases such as scurvy may be the result of defects in this hydroxylation, for example mutations in the enzyme prolyl hydroxylase or lack of the necessary cofactor of ascorbate (vitamin C).

Isomerización Cis-trans

Peptide bonds to Proline and other N-substituted amino acids (such as sarcosine ) are capable of populating the Cis and trans isomers.

Most peptide bonds overwhelmingly adopt the trans isomer (typically 99.9% under untrained conditions), mainly because the hydrogen amide (trans isomer) offers less steric repulsion to the preceding Cα atom than the next Cα atom (cis isomer).

In contrast, the cis and trans isomers of the X-Pro peptide bond (where X represents any amino acid) undergo steric collisions with near substitution and have a much smaller energy difference.

Therefore, the fraction of X-Pro peptide bonds in the cis isomer under untrained conditions is significantly high, with cis fractions typically in the range of 3-10%.

However, these values ​​depend on the preceding amino acid, with Gly and aromatic moieties that produce increased fractions of the cis isomer.

Cis fractions of up to 40% have been identified for Aromatic-Pro peptide bonds

From a kinetic point of view, cis-trans-Proline isomerization is a very slow process that can impede the advancement of protein folding by trapping one or more crucial proline residues for folding in the non-native isomer, especially when the native protein requires the cis isomer.

This is because the Proline residues are synthesized exclusively in the ribosome as the trans isomer form. All organisms possess prolyl isomerase enzymes to catalyze this isomerization, and some bacteria have specialized prolyl isomerases associated with the ribosome.

However, not all Prolines are essential for folding, and protein folding can proceed at a normal rate despite having non-native conformers of many X-Pro peptide bonds.


Proline and its derivatives are often used as asymmetric catalysts in organocatalysis reactions with Proline. The reduction of CBS and the aldol condensation catalyzed by Proline are outstanding examples.

In brewing, Proline-rich proteins are combined with polyphenols to produce turbidity (turbidity).

L-Proline is an osmoprotector and, therefore, is used in many pharmaceutical and biotechnological applications.

The growth medium used in the cultivation of plant tissues can be supplemented with Proline. This can increase growth, perhaps because it helps the plant tolerate the stresses of tissue culture.

To know the role of Proline in the stress response of plants, see § Biological activity.

Role and Benefits of Proline

Proline is associated with the production of collagen that promotes healthy skin, joints, tendons and heart muscle.

Proline helps strengthen the heart muscle, the metabolism of Proline is connected to enzymes that require niacin and vitamin C.

It helps strengthen the heart muscle, improves the texture of the skin and helps the formation of collagen and helps to contain the loss of collagen during aging.

Proline gives rise to glutamic acid which is an important amino acid. This glutamic acid gives rise to very important compounds such as glutathione, glutamine, gamma aminobutyric acid, alpha ketoglutarate, etc.

Proline is interchangeable with ornithine, so it can also lead to the formation of urea. On the other hand, it has also been found that ornithine forms Proline. Proline is also converted to hydroxyProline by post-translational reaction that occurs after it has been incorporated into the protein molecule.

Therefore, Proline is also an important amino acid. Your supplements are also available in the market. These are especially important in those people who suffer from diseases due to collagen deficiency and also in those who suffer from skin disorders and injuries.

Collagen in the skin contains hydroxyProline and hydroxylysine, which is formed from Proline and lysine, in which ascorbic acid appears to be important in this conversion. Collagen contains approximately 15% Proline. It is also believed to be important in maintaining muscles, joints and tendons.

Rich Sources of Proline Foods

It is not so necessary to obtain it from food, since it is formed in our body. But it is rich in meat, many of the sources include:

Asparagus, avocados, bamboo shoots, beans, brewer’s yeast, broccoli, brown rice bran, cabbage, caseinate, chives, dairy products, eggs, fish, lactalbumin, legumes, meat, nuts, seafood, seaweed, seeds, soy, spinach, watercress, buttermilk, whole grains.

Symptoms of Proline Deficiency

None : easily obtained and available to the body.


Proline is one of the two amino acids that do not follow the typical Ramachandran pattern, together with glycine . Due to the formation of the ring connected to the beta carbon, angles ψ around the peptide bond have less allowable degrees of rotation.

As a result, it is often found in “turns” of proteins since its free entropy (ΔS) is not as comparatively large as for other amino acids and, therefore, in a folded vs. unfolded form, the change in entropy is less .

In addition, Proline is rarely found in α and β structures, since it would reduce the stability of such structures, because its α-N side chain can only form a hydrogen bond.

In addition, Proline is the only amino acid that does not form a blue / purple color when developed by spraying with ninhydrin for use in chromatography. The Proline, on the other hand, produces an orange / yellow color.