Glycyl-alanyl-L-leucine

Other Names

2-[2-[(2-aminoacetyl)amino]propanoylamino]-4-methylpentanoic acidGly-Ala-Leuglycyl-alanyl-leucineGlycyl-L-alanyl-L-leucineH-Gly-Ala-Leu-OHL-Leucine, glycyl-L-alanyl-L-Leucine, N-(N-glycyl-L-alanyl)-NSC 335984NSC335984

Synopsis

Glycyl-Alanyl-L-Leucine (Gly-Ala-Leu)

1. Identity and Chemical Characterization

1.1 Names and Identifiers

Glycyl-alanyl-L-leucine is a linear tripeptide composed of three proteinogenic amino acids — glycine, L-alanine, and L-leucine — assembled in that N-to-C-terminal sequence. Its molecular formula is C₁₁H₂₁N₃O₄. Its IUPAC name is 2-[2-[(2-aminoacetyl)amino]propanoylamino]-4-methylpentanoic acid; it is registered under CAS number 22849-49-6 and carries synonyms including Gly-Ala-Leu, NSC335984, and L-Leucine, N-(N-glycyl-L-alanyl)-. It is catalogued in PubChem under Compound Identifier (CID) 6992585.

Its molecular weight is approximately 259.3 g/mol, and its physicochemical properties — including solubility and stability — are influenced by the hydrophobic leucine residue and the small glycine moiety. Glycyl-alanyl-leucine is moderately soluble in water due to the glycine residue, but less soluble than purely polar peptides such as glycyl-glycine.

1.2 Stereochemistry and Sequence

The compound is a tripeptide composed of glycine, L-alanine, and L-leucine residues, assembled through sequential peptide bond formation, where glycine is linked to the N-terminal of L-alanine, which is further connected to L-leucine. This compound belongs to the broader class of oligopeptides and shares structural similarities with other di- and tripeptides derived from proteinogenic amino acids.

1.3 Structural Features and Conformation

The Gly-Ala-Leu sequence belongs to a series of tripeptides of the general form Gly-L-Ala-X (where X is a branched-chain residue) that have been studied by X-ray crystallography specifically to probe alpha-helix nucleation. A 1991 study published in Biopolymers reported the crystal structures of Gly-L-Ala-L-Val and Gly-L-Ala-L-Leu, with discussion of sequence preference for nucleation of the alpha-helix and comments on the geometry of leucine zippers (Chaturvedi, Go, and Parthasarathy, PMID 1863691). THz spectroscopic studies of the crystalline form of Gly-Ala-Leu and related peptide–water systems have also been reported in the literature, further characterizing its solid-state dynamics.

The inclusion of leucine confers hydrophobicity to the tripeptide, while glycine enhances conformational flexibility. Cyclic peptides — for example, cyclo(glycyl-L-leucyl) — exhibit greater metabolic stability compared to linear analogs such as Gly-Ala-Leu.

1.4 Natural Occurrence and Source

Gly-Ala-Leu is not a major abundant peptide identified intact at high concentrations in human blood following dietary protein ingestion (in the way that proline/hydroxyproline-containing collagen peptides have been documented). However, its three constituent amino acids — glycine, alanine, and leucine — are among the eighteen amino acids present in collagen. Alanine, glycine, and leucine are all found in collagen, which contains eighteen amino acids including glycine, hydroxyproline, and proline as the most abundant components. Gly-Ala-Leu could therefore theoretically arise as a hydrolysis fragment during enzymatic or chemical degradation of collagen-rich proteins, though it has not been specifically identified as a major circulating collagen-derived peptide in published pharmacokinetic studies.

Glycyl-alanyl-L-leucine is considered a synthetic tripeptide composed of glycine, alanine, and leucine; while it is not established as a significant naturally occurring peptide entity, its constituent amino acids are essential building blocks in human nutrition and metabolism.

1.5 Common Forms and Preparations

Glycyl-alanyl-leucine is classified as a peptide. In research and commercial contexts it is available primarily as a chemically synthesized white solid or powder. It is shipped under ambient temperature as a non-hazardous chemical and is stable enough for short-term transport; recommended storage is dry, dark, and at 0–4°C for short-term use (days to weeks) or −20°C for long-term preservation (months to years). As a dietary supplement ingredient, it would typically be formulated as a powder, capsule, or added to protein/amino acid blend products, though no specific commercial dosage form has been characterized in peer-reviewed literature for this specific tripeptide. Its synthesis is performed by standard solid-phase peptide synthesis techniques, connecting glycine to L-alanine and then L-alanine to L-leucine through consecutive peptide-bond formations.

2. Traditional and Historical Use

2.1 Absence of Direct Traditional Use Records

The use of glycyl-alanyl-L-leucine as a distinct entity in traditional medicinal systems is not well documented; its components — particularly the amino acids — have a rich history of medicinal and nutritional application. No pharmacopeial monograph, WHO monograph, ESCOP monograph, or German Commission E entry exists for this specific tripeptide, reflecting the fact that it was not recognized or isolated as a discrete therapeutic substance in historical medicine. It does not appear in traditional Chinese medicine, Ayurvedic medicine, or Western herbal texts as a named ingredient.

2.2 Constituent Amino Acids in Historical Context

Although the tripeptide as such has no documented traditional use, it is relevant to note the historical recognition of protein-rich foods as medicinal. Ancient medical traditions across cultures prescribed concentrated broths, fermented dairy, legume preparations, and animal-derived gelatins for wound healing, recovery from illness, and support of physical strength. These preparations would have contained all three constituent amino acids — glycine, alanine, and leucine — in peptide-bound and free forms, without knowledge of their molecular identity.

Glycine was first isolated from acid hydrolysates of protein in 1820 by French chemist H. Braconnot; its name was derived from the Greek word "glykys" owing to its sweet taste, and it was chemically synthesized by A. Cahours from monochloroacetic acid and ammonia, who established its structure. The identification of individual amino acids, including alanine and leucine, proceeded through the nineteenth century, and research into their biological roles and combination into peptides is a phenomenon of twentieth-century biochemistry.

Historically, research into small peptides like glycyl-alanyl-L-leucine has focused on their potential for enhanced absorption and bioavailability compared to free amino acids, particularly in clinical nutrition and sports supplementation. This research interest arose largely in the latter decades of the twentieth century after the characterization of intestinal peptide transporters.

3. Key Constituents and Mechanisms of Action

3.1 Constituent Amino Acids

Glycyl-alanyl-L-leucine is composed entirely of three amino acids, each with established biochemical roles:

Glycine (Gly, G): The smallest and simplest amino acid, with no chiral center. Glycine acts as a precursor for several key metabolites of low molecular weight, including creatine, glutathione, haem, purines, and porphyrins. In collagen, glycine is located at every third position, and glycine residues bring together the triple helix of the collagen. Glycine lowers the level of superoxide ions from neutrophils through glycine-gated chloride channels; tumor necrosis factor, inflammation, and activation of macrophages are inhibited by glycine.
L-Alanine (Ala, A): A non-essential amino acid involved in energy metabolism, particularly the glucose-alanine cycle. Glycine and alanine together show a special character in improving alcohol metabolism. Alanine is a major gluconeogenic amino acid released from skeletal muscle during fasting and exercise, and is present throughout connective tissue proteins.
L-Leucine (Leu, L): An essential branched-chain amino acid (BCAA) that functions as a critical regulator of protein anabolic signaling. Leucine activates mammalian target of rapamycin (mTOR) to upregulate protein synthesis. mTORC1 signals to ribosomal protein S6 protein kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4EBP1), which are the two best-known downstream effectors of mTOR signalling and control the protein synthetic pathway.

3.2 Intact Tripeptide Absorption: The PepT1 Transporter

A central mechanistic rationale for supplementing tripeptides rather than free amino acids rests on the intestinal peptide transport system. Bioactive di/tripeptides are among the most efficient structural units that can cross the intestinal barrier and reach the circulation owing to their small molecular size and compact conformation; evidence indicates that more than 70% of protein digestion products in the gastrointestinal tract are absorbed in the form of di/tripeptides, primarily via a specialized proton-coupled transport system.

The key mediator of this absorption process is peptide transporter 1 (PepT1), a proton-dependent oligopeptide transporter that is highly expressed at the brush-border membrane of intestinal epithelial cells. The intestinal peptide transporter 1 (PepT1) was first identified in 1994; it plays a crucial role in the absorption of small peptides including not only more than 400 different dipeptides and 8,000 tripeptides digested from dietary proteins but also a repertoire of structurally related compounds and drugs.

PepT1 (also known as oligopeptide transporter 1) is located in the apical membrane of intestinal enterocytes, operating as an electrogenic proton–peptide cotransporter; it is also known as solute carrier family 15 member 1 (SLC15A1); this transporter does not transport free amino acids or peptides containing four or more amino acid residues. As a tripeptide, Gly-Ala-Leu falls within the substrate size range recognized by PepT1, making it a potential PepT1 substrate, though specific transport kinetics for this particular sequence have not been characterized in published peer-reviewed studies.

PepT1 plays a key role in the supply of nitrogen to the body; it absorbs di- and tripeptides released by the digestion of dietary or endogenous proteins from the small intestine. As a high capacity, low affinity transporter of peptides, PepT1 is not likely to saturate even at the very high substrate concentrations typically encountered in the intestine.

3.3 Post-Absorptive Metabolism and Amino Acid Release

The transport system carries peptides from a region with low dipeptidase activity (intestinal lumen) to a region with high dipeptidase activity (enterocyte cytoplasm). Once inside the enterocyte, tripeptides such as Gly-Ala-Leu are expected to be hydrolyzed by cytosolic peptidases into their constituent free amino acids — glycine, L-alanine, and L-leucine — which then enter portal circulation and participate in systemic metabolism. Gly-Ala-Leu may also enter portal circulation as an intact peptide, though quantitative data specific to this sequence are not available in the published literature.

3.4 Physicochemical Properties Relevant to Bioactivity

The leucine residue at the C-terminal position confers hydrophobicity to the tripeptide, while the N-terminal glycine residue enhances conformational flexibility. Di/tripeptide transport efficiency through PepT1 is influenced by peptide structure, meaning that the specific sequence, charge, and hydrophobicity of Gly-Ala-Leu would modulate how efficiently the transporter handles it relative to other tripeptides. Although the transport of amino acids is mediated by several specific amino acid transporters, the proton-coupled uptake of more than 8,000 different di- and tripeptides is performed by the high-capacity/low-affinity peptide transporter isoform PEPT1 (SLC15A1).

4. Scientific Evidence by Area

4.1 Important Evidential Limitation: Absence of Specific Human Clinical Trials

A critical finding from a thorough search of the primary literature (PubMed/PMC, PubChem, and related scientific databases) is that no human clinical trials, systematic reviews, or even preclinical (animal or cell-based) intervention studies have been published specifically investigating glycyl-alanyl-L-leucine as a standalone dietary supplement or therapeutic agent. Published scientific studies involving this compound are confined to structural chemistry (X-ray crystallography and spectroscopy of the solid state) and its commercial availability as a research reagent. The following sections therefore address the evidence base for its constituent amino acids in relevant functional areas, clearly identified as such, and distinguish these from any evidence bearing on the intact tripeptide itself.

4.2 Skeletal Muscle Protein Synthesis and Exercise Recovery

The most discussed potential application of Gly-Ala-Leu as a supplement ingredient relates to its leucine content and the leucine residue's well-characterized role in activating muscle protein synthesis. Ingestion of a leucine-enriched essential amino acid nutrient solution rapidly and potently activates the mammalian target of rapamycin (mTOR) signalling pathway and protein synthesis in human skeletal muscle; furthermore, mTOR signalling and muscle protein synthesis are enhanced when leucine-enriched nutrients are ingested following resistance exercise.

The addition of leucine to regular meals may improve the ability of feeding to stimulate protein synthesis in old human muscle. Research on leucine-containing dipeptides has extended this reasoning to the peptide form: a study evaluating dileucine (L-leucyl-L-leucine) investigated plasma and intramuscular leucine and dileucine concentrations and phosphorylation of downstream mTORC1 signaling proteins, also including an exploratory analysis of various commercially available intact protein sources for their di- and tripeptide content.

Evidence strength for Gly-Ala-Leu specifically: No clinical or preclinical study has directly tested this tripeptide for muscle protein synthesis. The mechanistic rationale is indirect and inferred from the well-documented role of the leucine residue and from general principles of di/tripeptide absorption. Any claim of a direct anabolic effect for the intact tripeptide Gly-Ala-Leu in humans remains without published evidential support.

4.3 Collagen Synthesis and Connective Tissue Health

Research on collagen hydrolysates has identified certain small peptides derived from collagen digestion that can be detected intact in human blood after oral ingestion. Gly-Pro-Hyp (glycyl-prolyl-hydroxyproline) is the signature collagen tripeptide, absorbed intact and detectable in plasma and skin tissue following oral ingestion; the unique ring structures of proline and hydroxyproline confer rigidity and resistance to hydrolysis by standard digestive peptidases, explaining how these peptides survive gastrointestinal transit intact. Additional peptides detected in human blood after gelatin hydrolysate ingestion include Ala-Hyp, Ala-Hyp-Gly, Pro-Hyp-Gly, Leu-Hyp, Ile-Hyp, and Phe-Hyp.

Gly-Ala-Leu does not contain hydroxyproline or proline and therefore does not share the resistance to gastrointestinal peptidases that has been demonstrated for the hydroxyproline-containing collagen peptides listed above. Its constituent amino acids — glycine, alanine, and leucine — are all found in collagen. Research on free amino acids has shown that among the free amino acids tested in cultured human dermal fibroblasts, glycine increased collagen production most effectively, followed by proline, isoleucine, glutamine, and leucine. However, this in-vitro observation with free amino acids does not establish an effect for the intact Gly-Ala-Leu tripeptide.

Approximately 5% of amino acids in muscle contractile protein are glycine, and one-third in structural proteins such as collagen and elastin, highlighting its importance in muscle connective tissue and the extracellular matrix; as a protein precursor, glycine contributes to collagen synthesis.

Evidence strength for Gly-Ala-Leu specifically: There are no studies testing this tripeptide in collagen synthesis or connective-tissue endpoints. The evidence base is entirely limited to the constituent amino acids in free or hydroxyproline-containing peptide forms.

4.4 Protein Digestion, Nitrogen Absorption, and Clinical Nutrition

The broader rationale for tripeptide supplementation in clinical nutrition draws on the established physiology of intestinal peptide transport. Studies on di- and tripeptides have demonstrated that they can be absorbed intact via specialized peptide transporters in the intestine, offering potential advantages for individuals with compromised digestive function or increased nutritional needs. It is well established that dietary proteins are absorbed as di- and tripeptides rather than free amino acids.

Clinical enteral and parenteral nutrition research has used peptide-based nitrogen sources, but this literature addresses peptide mixtures or defined di/tripeptides such as Gly-Gln or Ala-Gln — not Gly-Ala-Leu specifically. The glutamine-containing dipeptide Ala-Gln has the most substantial clinical nutrition evidence base among individual small peptides. Gly-Ala-Leu has not appeared as a subject in any clinical nutrition trial.

Evidence strength for Gly-Ala-Leu specifically: Theoretical (mechanism-based), with no direct clinical data.

4.5 Glycine-Mediated Anti-Inflammatory and Cytoprotective Properties

Glycine, as a free amino acid and as an ingredient of the tripeptide's N-terminal residue, has documented anti-inflammatory properties studied primarily in animal and cell models. Tumor necrosis factor, inflammation, and activation of macrophages are inhibited by glycine; glycine also reduces alcohol-induced liver damage and removes lipid peroxidation reperfusion injury and glutathione deficiency caused by several types of hepatotoxins. Dietary supplementation of appropriate doses of glycine is reported as effective in treating metabolic disorders in patients with cardiovascular diseases, several inflammatory diseases, obesity, cancers, and diabetes — though the quality and size of human trials vary considerably and many reports are based on preclinical data.

Cell, in vitro, and animal studies suggest that glycine enhances protection against muscle wasting by activating anabolic pathways and inhibiting proteolytic gene expression; some evidence indicates that glycine supplementation may enhance peak power output, reduce lactic acid accumulation during high-intensity exercise, and improve sleep quality and recovery. More randomized controlled clinical trials in humans are needed to confirm glycine's potential as a dietary supplement to support muscle function, recovery, and overall athletic performance.

Evidence strength for Gly-Ala-Leu specifically: None; these are properties of free glycine, not of the intact tripeptide.

4.6 Structural Chemistry: Alpha-Helix Nucleation Studies

The primary body of peer-reviewed literature referencing Gly-Ala-Leu as a compound is in structural chemistry, not nutrition or pharmacology. The 1991 Biopolymers paper (Chaturvedi, Go, and Parthasarathy) investigated a sequence preference for nucleation of the alpha-helix using the crystal structures of Gly-L-Ala-L-Val and Gly-L-Ala-L-Leu, with comments on the geometry of leucine zippers. A subsequent 1992 Biopolymers study by Go et al. examined the closely related isomeric tripeptide Gly-L-Ala-L-Ile (GAI), finding that attempts to design crystalline alpha-helical peptides led to synthesis and crystallization of GAI (C₁₁H₂₁N₃O₄, the isomeric tripeptide with isoleucine) in two crystal forms, where form 1 (GAI1) is isomorphous with GAV and forms a helix, while form 2 does not; in GAI1, the tripeptide molecule is held in a near-helical conformation by a water molecule that bridges the NH₃⁺ and COO⁻ groups, acting as the fourth residue needed to complete the turn. These structural studies illustrate that the Gly-Ala-X tripeptide family (where X is a branched-chain residue) can nucleate helical conformations, which has theoretical relevance for peptide drug design but does not bear on dietary supplement claims.

Additional solid-state spectroscopic investigations of crystalline Gly-Ala-Leu and related peptide-water systems have also been reported in the THz spectroscopy literature (Ahmed et al., Faraday Discussions, 2011, PMID 22457948) and solid-state NMR studies (Pometun et al., J Am Chem Soc, 2002, PMID 11878990), all of which are mechanistic structural investigations rather than biological activity studies.

5. Body Systems and Health Areas of Association

The following associations are based on the biochemistry of constituent amino acids and general peptide science. They are not supported by clinical trials conducted on Gly-Ala-Leu itself:

Musculoskeletal system: Leucine's role as the primary amino acid signal for mTORC1-dependent muscle protein synthesis makes any leucine-containing tripeptide of theoretical interest for muscle maintenance and exercise recovery. Glycine and alanine are structural components of muscle connective tissue and collagen.
Connective tissue and extracellular matrix: All three constituent amino acids are present in collagen; glycine at every third position in the collagen triple helix is structurally indispensable. In collagen, glycine is located at every third position and brings together the triple helix.
Gastrointestinal nitrogen absorption: Bioactive di/tripeptides have become key components in functional foods due to their excellent bioactivity and absorption properties; however, their oral bioavailability is limited by the complexity of intestinal absorption processes, primarily relying on PepT1 for transmembrane transport.
Hepatic and metabolic health: Some functions of glycine include bile acid conjugation and it has a vital role in many reactions such as haem, purine, and gluconeogenesis; glycine along with alanine shows a special character to improve alcohol metabolism.
Central nervous system: Glycine has the property to enhance sleep quality and neurological functions. Glycine is a recognized inhibitory neurotransmitter in the spinal cord and brainstem, functioning through glycine-gated chloride channels.
Antioxidant defense: Glycine acts as a precursor for glutathione, the major intracellular antioxidant tripeptide (γ-Glu-Cys-Gly), providing a substrate link between glycine availability and oxidative stress defense, though glutathione synthesis depends on all three of its own constituent amino acids and is not directly driven by Gly-Ala-Leu.

6. Dosage Forms and Reported Dosages

No human clinical study has established a dosage regimen for glycyl-alanyl-L-leucine as a dietary supplement. No regulatory body — including the U.S. Food and Drug Administration (FDA), European Food Safety Authority (EFSA), European Medicines Agency (EMA), or WHO — has issued a guidance document or monograph specifying a dose for this tripeptide.

The compound is commercially available in research quantities primarily through laboratory chemical suppliers; it is not routinely held in stock and may be available through custom synthesis, with a minimum order quantity of 1 gram for research purposes.

Dosages reported in the peer-reviewed literature for the constituent free amino acids provide the only available reference points (these relate to the free amino acids, not the intact tripeptide):

In human studies of collagen hydrolysate (a source of multiple glycine-, alanine-, and leucine-containing peptides), healthy human volunteers ingested gelatin hydrolysates of 9.4–23 g from porcine skin, chicken feet, and cartilage after 12 hours of fasting in pharmacokinetic studies — though these studies tracked hydroxyproline-containing peptides, not Gly-Ala-Leu.
In human leucine supplementation studies, dosages of isolated leucine and leucine-enriched essential amino acid solutions have been studied; specific doses vary widely by study design and are not generalizable to the tripeptide form.

Until clinical studies are conducted with defined doses of the intact tripeptide, no evidence-based dosage recommendation can be stated for glycyl-alanyl-L-leucine.

7. Safety Considerations and Interactions

7.1 Constituent Amino Acid Safety Profile

All three constituent amino acids — glycine, L-alanine, and L-leucine — are normal dietary components found in every protein-containing food and have been consumed by humans in large quantities throughout history. They are classified as Generally Recognized As Safe (GRAS) by the U.S. FDA for use in food. No toxicological concerns have been raised for glycyl-alanyl-L-leucine in the published literature.

Shortage of glycine in small quantities is not harmful for health, but severe shortage may lead to failure of immune response, low growth, abnormal nutrient metabolism, and undesirable health effects; glycine is considered a conditionally essential amino acid for humans and other mammals to support good growth.

7.2 PepT1 Transporter Interactions

Because Gly-Ala-Leu is a tripeptide and thus a potential substrate for the intestinal PepT1 transporter, competitive interactions at this transporter are theoretically possible with drugs and other peptides that also use PepT1. A food-drug interaction between milk and the PepT1 substrate oseltamivir has been reported; in vitro investigations suggest that quinolone antibiotics such as moxifloxacin may interfere with the absorption of PepT1 substrates, and a mutual inhibition of PepT1- and OAT1/3-driven absorption may exist between the protease inhibitor bestatin and cefixime. Whether Gly-Ala-Leu specifically interferes with the absorption of any drug has not been studied.

In healthy individuals, PepT1 is primarily expressed in the small intestine and transports di/tripeptides for metabolic purposes; however, during chronic inflammation such as inflammatory bowel disease, PepT1 expression is upregulated in the colon. This upregulation could theoretically alter absorption kinetics of peptide supplements in patients with inflammatory bowel disease, but this has not been specifically investigated for Gly-Ala-Leu.

7.3 Overall Safety Assessment

In the absence of any published human clinical or safety study specifically for this tripeptide, its safety profile can only be inferred from the established safety of its constituent amino acids at physiological concentrations. It is classified as a non-hazardous chemical under standard shipping regulations. No known contraindications, adverse events, or drug interactions have been reported for glycyl-alanyl-L-leucine in the peer-reviewed literature, nor has any regulatory authority flagged safety concerns for this specific compound. The strength of this absence-of-evidence safety inference is inherently limited by the lack of formal human safety studies.

8. Summary of Evidence Strength

The following table summarizes the current state of evidence for glycyl-alanyl-L-leucine across the domains discussed in this article:

Chemical identity and structural characterization: Well-established; registered in PubChem (CID 6992585), CAS 22849-49-6; crystal structure of closely related analogs published.
Intestinal absorption via PepT1 (general tripeptides): Robustly established for the tripeptide class as a whole; specific data for Gly-Ala-Leu not available.
Muscle protein synthesis: Strong evidence for L-leucine (free amino acid); no evidence for the intact Gly-Ala-Leu tripeptide.
Collagen and connective tissue support: Moderate evidence for constituent free amino acids (especially glycine) in cell and animal models; no evidence for intact Gly-Ala-Leu.
Anti-inflammatory and cytoprotective effects: Moderate preclinical evidence for free glycine; no evidence for intact Gly-Ala-Leu.
Human clinical efficacy for any health outcome: No published data.
Human safety: No formal safety studies published. Inferred to be low-risk from constituent amino acid GRAS status.

While more targeted research is needed to fully establish the unique benefits of glycyl-alanyl-L-leucine, its formulation in nutritional products leverages established principles of peptide nutrition; its inclusion is based on scientific rationale, and ongoing research may further elucidate specific contributions to health and performance. As of the time of publication of this article, no human clinical trial, systematic review, or preclinical intervention study has been registered or published that directly evaluates this tripeptide as a dietary supplement.

References

Health Conditions

Health conditions that Glycyl-alanyl-L-leucine may help support.

No conditions available.

Body Systems

Body systems that Glycyl-alanyl-L-leucine may help support.

No body systems available.