glicil-alanil-lisina-L-valina

Glycyl-Alanyl-Lysine-L-Valine

1. Identity and Chemical Characterization

Glycyl-alanyl-lysine-L-valine is a synthetic tetrapeptide composed of four amino acid residues joined in sequence by peptide bonds: glycine (Gly), alanine (Ala), lysine (Lys), and L-valine (Val), in that N-terminal to C-terminal order. It is a synthetic peptide composed of the amino acids glycine, alanine, lysine, and valine.

A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. Many tetrapeptides are pharmacologically active, often showing affinity and specificity for a variety of receptors in protein-protein signaling. Present in nature are both linear and cyclic tetrapeptides, the latter of which mimics protein reverse turns which are often present on the surface of proteins and druggable targets.

The tetrapeptide does not appear in major chemical databases such as PubChem under a consolidated entry for the four-residue sequence Gly-Ala-Lys-Val (the related tripeptide glycyl-L-alanyl-L-lysine bears PubChem CID 71404690, and glycyl-alanyl-valine bears CID 129439, but the full tetrapeptide sequence does not carry an established CAS Registry Number in widely-cited sources at the time of this writing). The ingredient is identified in nutritional product labeling predominantly under the IUPAC-style name "glycyl-alanyl-lysine-L-valine," reflecting the stereospecific inclusion of the L-enantiomer of valine at the C-terminus.

Natural occurrence. Tetrapeptide fragments are produced during protein digestion in the small intestine as intermediate hydrolysis products. Naturally occurring tetrapeptide sequences are released from collagen, casein, and other food proteins through enzymatic digestion. While the specific sequence Gly-Ala-Lys-Val may arise transiently as a digestion intermediate from dietary proteins that contain this adjacent motif, this specific tetrapeptide does not have a documented history as a traditional medicinal remedy in ancient texts; its constituent amino acids have long been recognized for their vital roles in human health and nutrition.

Common forms and preparations. Glycyl-alanyl-lysine-L-valine is not available as a stand-alone bulk ingredient with established pharmacopeial monographs. In recent years, the use of tailored peptides like glycyl-alanyl-lysine-L-valine in nutritional products has grown, reflecting modern advances in understanding protein metabolism and the specific benefits of amino acid sequences. It appears primarily as one component among multiple peptide ingredients listed on the labels of sports nutrition powders (particularly post-workout amino acid blends), capsules, and functional food products. No official pharmacopeial monograph (USP, European Pharmacopoeia, BP, WHO) for this specific tetrapeptide has been identified in current literature.

2. Traditional and Historical Use

This specific tetrapeptide does not have a documented history as a traditional medicinal remedy in ancient texts; its constituent amino acids have long been recognized for their vital roles in human health and nutrition. Historically, foods rich in these amino acids—such as legumes, grains, and meats—have been valued in various cultures for their restorative and nourishing properties, often incorporated into broths, tonics, and healing diets to promote recovery and vitality.

The tetrapeptide as a discrete chemical entity is entirely a product of modern synthetic peptide chemistry. There is no record of its deliberate preparation or use in Ayurvedic, Traditional Chinese Medicine, Galenic, Unani, or any other historical system. Any association with "traditional" practice is derived indirectly from the longstanding role of its four constituent amino acids in food traditions—not from the tetrapeptide molecule itself.

In recent years, the use of tailored peptides like glycyl-alanyl-lysine-L-valine in nutritional products has grown, reflecting modern advances in understanding protein metabolism and the specific benefits of amino acid sequences. Historically, research into peptide supplementation has focused on enhancing protein bioavailability, supporting muscle health, and modulating immune responses. This modern research context — not ancient tradition — is the foundation on which the ingredient is currently marketed.

3. Constituent Amino Acids and Their Established Biology

Because glycyl-alanyl-lysine-L-valine is composed of four amino acids whose individual roles have been independently studied, understanding the tetrapeptide requires a review of each component. The following sections summarize the established biology of each constituent. This information describes the amino acids individually; it does not constitute evidence for effects of the intact tetrapeptide.

3.1 Glycine

Glycine is the proteinogenic amino acid of lowest molecular weight, harboring a hydrogen atom as a side chain. In addition to being a building block for proteins, glycine is also required for multiple metabolic pathways, such as glutathione synthesis and regulation of one-carbon metabolism. Although generally viewed as a non-essential amino acid, because it can be endogenously synthesized to a certain extent, glycine has also been suggested as a conditionally essential amino acid.

Glycine acts as a precursor for several key metabolites of low molecular weight such as creatine, glutathione, haem, purines, and porphyrins. 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.

Metabolic benefits mediated by glycine include the inhibition of oxidative stress via increased glutathione biosynthesis, an inhibitory effect on gluconeogenesis and food intake via activation of the NMDA receptor, curbing the overload. Glycine also exerts positive effects on mitochondrial activity via heme biosynthesis, detoxification processes via urinary excretion of glycine conjugates, and regulation of hormonal (enhanced secretion of key hormones in glucose homeostasis) and cytokine (reduced production of pro-inflammatory cytokines) responses via activation of glycine receptors (GlyRs).

As a cautionary note, current conclusions cannot extend beyond a dose of 15 g of glycine per day, which is the highest dose well tolerated in adult humans.

3.2 Alanine

Alanine and glutamine are the principal glucogenic amino acids. Most originate from muscles, where branched-chain amino acids (valine, leucine, and isoleucine) are nitrogen donors and, under exceptional circumstances, a source of carbons for glutamate synthesis. Glutamate is a nitrogen source for alanine synthesis from pyruvate and a substrate for glutamine synthesis by glutamine synthetase.

Alanine plays a significant role during early starvation, exposure to high-fat and high-protein diets, and diabetes. Glutamine acts as a substrate for gluconeogenesis in the liver, kidneys, and intestine, whereas alanine does so only in the liver. Glycine along with alanine show special character to improve alcohol metabolism.

3.3 Lysine

Lysine (L-lysine) is one of nine essential amino acids that the human body cannot synthesize and must obtain from dietary sources. It plays fundamental roles in protein synthesis, collagen formation, calcium absorption, immune function, and the production of carnitine — a molecule essential for fatty acid metabolism and energy production.

Lysine is essential for the synthesis of collagen and elastin; the formation of crosslinks with glutamine resistant to mechanical influences; and the stabilization of the extracellular matrix, hemostasis, and the activation of growth factors. Lysine has been suggested in the form of creams, gels, and sprays to support wound healing. Beneficial effects of lysine and lysine hyaluronate have been reported in the management of diabetic foot ulcers, hospitalized patients with decubitus ulcers, and chemo/radiotherapy-induced oral mucositis.

The adult requirement for lysine is approximately 30–35 mg per kilogram of body weight per day, which translates to roughly 2,100–2,450 mg daily for a 70 kg adult. The World Health Organization (WHO) sets the requirement at 30 mg/kg/day.

3.4 L-Valine

The branched-chain amino acids (BCAAs) are leucine, valine, and isoleucine. BCAAs are three of the nine indispensable amino acids, and are frequently consumed as a dietary supplement by athletes and recreationally active individuals alike.

Most alanine and glutamine originate from muscles, where branched-chain amino acids (valine, leucine, and isoleucine) are nitrogen donors and, under exceptional circumstances, a source of carbons for glutamate synthesis. Several studies have shown that BCAAs (particularly leucine) increase the phosphorylation status of key proteins within the mechanistic target of rapamycin (mTOR) signalling pathway involved in the regulation of translation initiation in human muscle.

Evidence indicates that leucine alone may exert an anabolic response, while no such data exists for isoleucine or valine. Valine's specific contribution to muscle protein synthesis, independent of leucine, thus remains insufficiently characterized by human clinical evidence.

4. Mechanisms of Action: General Bioactive Peptide Framework

As a functional ingredient in nutritional products, the use of glycyl-alanyl-lysine-L-valine is rooted in the understanding that peptides can have unique biological activities beyond the roles of their constituent amino acids.

The physiological activity of bioactive peptides is closely related to their structures, mainly including amino acid composition and sequence, molecular weight, amino acid type at the N-terminal/C-terminal, hydrophobic/hydrophilic property of amino acid chain, and amino acid charge property of peptides.

Many peptides function as hormones, neurotransmitters, enzyme substrates or inhibitors, growth promoters, or other regulatory molecules that selectively bind to their target receptors when necessary. They can be removed rapidly when their requirement expires, accounting for their rapid renal clearance (since the kidney usually filters out molecules below 60 kDa) and a shorter half-life lasting for a few minutes, thus losing their activity.

Emerging scientific studies suggest that certain bioactive peptides can act as signaling molecules, influencing metabolic pathways and supporting tissue regeneration. The inclusion of glycyl-alanyl-lysine-L-valine in nutritional products is based on this growing body of evidence, as well as preclinical research indicating that peptides with similar sequences may enhance protein synthesis and reduce muscle breakdown. However, this reasoning relies on analogy to related peptides, not on direct evidence for this specific sequence.

5. Intestinal Absorption and Bioavailability: A Critical Consideration

The intestinal absorption of the intact four-residue peptide is a key unresolved question that bears directly on the validity of any proposed mechanisms for glycyl-alanyl-lysine-L-valine as an intact molecule.

Intestinal protein digestion generates a huge variety and quantity of short chain peptides that are absorbed into intestinal epithelial cells by the PEPT1 transporter in the apical membrane of enterocytes. PEPT1 operates as an electrogenic proton/peptide symporter with the ability to transport essentially every possible di- and tripeptide. Transport is enantio-selective and involves a variable proton-to-substrate stoichiometry for uptake of neutral and mono- or polyvalently charged peptides. Neither free amino acids nor peptides containing four or more amino acids are accepted as substrates.

This point is reinforced by multiple independent sources. PepT1 can transport most of the 400 dipeptides and 8,000 tripeptides, but not free amino acids or tetrapeptides and larger peptides. As expected, single amino acids and tetrapeptides could not bind to or be transported by PEPT1.

The peptide binding cavity of PepT1 is reported to be approximately 13 × 12 × 11 Å, which limits the attachment to only di- and tripeptides, while it would be sterically restrictive for peptides with more than tetrapeptide length. Additionally, di- or tripeptides with a positive charge of +2 or greater (e.g., Lys-Lys) are poor substrates for PepT1 due to electrical repulsion with the co-transported proton. Given that lysine carries a positively charged side chain at physiological pH, this ionic consideration may further reduce any potential interaction with PEPT1 even if the structural size limitation were not operative.

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.

There is virtually no absorption of peptides longer than four amino acids. However, there is abundant absorption of di- and tripeptides in the small intestine. These small peptides are absorbed into the small intestinal epithelial cell by co-transport with H⁺ ions via a transporter called PepT1. Once inside the enterocyte, the vast bulk of absorbed di- and tripeptides are digested into amino acids by cytoplasmic peptidases and exported from the cell into blood. Only a very small number of these small peptides enter blood intact.

The practical consequence is that glycyl-alanyl-lysine-L-valine, if consumed orally, is most likely hydrolyzed by gastrointestinal and brush-border peptidases prior to or concurrent with enterocyte uptake, yielding its constituent free amino acids and di/tripeptide fragments rather than being absorbed as the intact four-residue sequence. There are no published pharmacokinetic studies specifically characterizing the oral bioavailability of the intact tetrapeptide in humans.

6. Scientific Evidence by Area of Use

No peer-reviewed human clinical trials, randomized controlled trials, or systematic reviews have been published specifically investigating glycyl-alanyl-lysine-L-valine as an isolated intervention. Glycyl-alanyl-lysine-L-valine itself has not been the subject of extensive clinical trials; related peptides have demonstrated beneficial effects in areas such as muscle recovery, improved nutrient absorption, and cellular repair. The following discussion therefore presents (a) evidence for the class of bioactive peptides in general and (b) evidence for the constituent amino acids, clearly distinguished from one another.

6.1 Muscle Recovery and Physical Performance

Bioactive peptides (general class): Food-derived bioactive peptides are physiologically active peptides mostly derived from proteins following hydrolysis, which could be resorbed in intact form to reduce muscle damage following exercise and induce beneficial adaptations within the connective tissue. However, the complexity of the histoarchitectural considerations for skeletal muscle injuries and the repair mechanism of damaged skeletal muscle are not well known.

BCAAs including valine: The popularity of BCAA supplements is largely predicated on the notion that they can stimulate rates of muscle protein synthesis (MPS) and suppress rates of muscle protein breakdown (MPB), the combination of which promotes a net anabolic response in skeletal muscle. To date, several studies have shown that BCAAs (particularly leucine) increase the phosphorylation status of key proteins within the mTOR signalling pathway involved in the regulation of translation initiation in human muscle. Early research in humans demonstrated that BCAA provision reduced indices of whole-body protein breakdown and MPB; however, there was no stimulatory effect of BCAA on MPS.

Evidence supporting the efficacy of branched-chain amino acids alone for muscle hypertrophy in humans is somewhat equivocal. Specifically regarding valine as an individual BCAA: the responses to individual BCAAs (i.e., leucine, valine, or isoleucine) might differ from the combination of the three for several reasons. Evidence indicates that leucine alone may exert an anabolic response, while no such data exists for isoleucine or valine.

Evidence quality for glycyl-alanyl-lysine-L-valine specifically: No direct clinical evidence exists. Evidence for the BCAA-containing class to which valine belongs is mixed and largely attributable to leucine, not valine. Evidence level: preclinical and theoretical only for this specific peptide.

6.2 Connective Tissue, Collagen, and Wound Healing

Lysine is essential for the synthesis of collagen and elastin; the formation of crosslinks with glutamine resistant to mechanical influences; and the stabilization of the extracellular matrix, hemostasis, and the activation of growth factors. Lysine has been suggested in the form of creams, gels, and sprays to support wound healing. Beneficial effects of lysine and lysine hyaluronate have been reported in the management of diabetic foot ulcers, hospitalized patients with decubitus ulcers, and chemo/radiotherapy-induced oral mucositis.

Glycine is another prominent constituent of native collagen triple helices, where Gly–X–Y repeating sequences are essential to triple helix formation. There are overwhelming reports supporting the role of supplementary glycine in prevention of many diseases and disorders including cancer. Dietary supplementation of proper dose of glycine is effectual in treating metabolic disorders in patients with cardiovascular diseases, several inflammatory diseases, obesity, cancers, and diabetes. These findings relate to glycine as a free amino acid, not to its presence in this tetrapeptide.

Evidence quality for glycyl-alanyl-lysine-L-valine specifically: No direct clinical evidence. Inference from lysine and glycine biochemistry. Evidence level: indirect, constituent-based only.

6.3 Metabolic and Gluconeogenic Roles

Alanine and glutamine are the principal glucogenic amino acids. Alanine plays a significant role during early starvation, exposure to high-fat and high-protein diets, and diabetes. The alanine–glucose cycle—where alanine is released from muscle under catabolic conditions and transported to the liver for gluconeogenesis—is a well-characterized metabolic pathway, but this relates to free alanine, not to alanine in peptide form.

Metabolic benefits mediated by glycine include the inhibition of oxidative stress via increased glutathione biosynthesis, an inhibitory effect on gluconeogenesis and food intake via activation of the NMDA receptor.

Evidence quality for glycyl-alanyl-lysine-L-valine specifically: No direct clinical evidence. Evidence for constituent free amino acids: moderate to strong for individual metabolic roles. Evidence level: indirect, constituent-based only.

6.4 Immune Function

Lysine plays fundamental roles in protein synthesis, collagen formation, calcium absorption, and immune function. L-lysine is crucial for the synthesis and structural integrity of collagen, supporting skin, bones, and connective tissues. It significantly contributes to immune system strength by aiding in antibody production and potentially inhibiting certain viral activities.

Tumor necrosis factor, inflammation, and activation of macrophages are inhibited by glycine. These effects have been documented at the level of isolated glycine supplementation in experimental settings, not for the intact tetrapeptide.

Evidence quality for glycyl-alanyl-lysine-L-valine specifically: No direct clinical evidence. Evidence for lysine and glycine on immune parameters: emerging but primarily in vitro and animal data. Evidence level: indirect, constituent-based only.

6.5 Antioxidant Activity

Glycine acts as a precursor for several key metabolites of low molecular weight such as creatine, glutathione, haem, purines, and porphyrins. Glutathione (γ-glutamylcysteinylglycine) is the principal cellular antioxidant, and glycine provides its C-terminal residue. This means glycine availability can influence glutathione synthesis.

Tripeptides have been examined for their bioactive properties, including antioxidant and anti-inflammatory effects, though further studies are necessary to establish these benefits in humans. The same caveat applies more forcefully to a tetrapeptide lacking direct clinical study.

Evidence quality for glycyl-alanyl-lysine-L-valine specifically: No direct evidence. Evidence for the general antioxidant class: limited in vitro and animal data for analogous peptides. Evidence level: preclinical/theoretical only.

7. Body Systems Associated with This Ingredient

• Musculoskeletal system: By virtue of containing valine (a BCAA) and lysine (required for collagen crosslinking), the tetrapeptide is positioned in sports-nutrition contexts as supporting skeletal muscle recovery and connective tissue integrity. The inclusion of glycyl-alanyl-lysine-L-valine in nutritional products is based on preclinical research indicating that peptides with similar sequences may enhance protein synthesis and reduce muscle breakdown.
• Gastrointestinal and absorptive system: The tetrapeptide must first be processed by the GI tract; as discussed above, it is likely hydrolyzed to di/tripeptide fragments and free amino acids before systemic absorption. Proteins originating from the diet and from gastrointestinal secretions are digested by several gastric and pancreatic proteases, which are further acted upon by a cadre of peptidases in the brush border membrane of intestinal epithelium. Once inside the cell, cytoplasmic peptidases act on the di/tripeptides so that the majority of protein digestion products actually enter the portal vein in the form of amino acids.
• Immune system: Via its lysine and glycine components, some association with immune modulation has been proposed based on the established biology of those amino acids.
• Metabolic/hepatic system: Alanine as a gluconeogenic amino acid and glycine as a metabolic substrate for glutathione and heme biosynthesis connect the tetrapeptide's components to central metabolic pathways.

8. Dosage Forms and Reported Dosages

No clinical dosage for glycyl-alanyl-lysine-L-valine as an isolated ingredient has been established in peer-reviewed research. The tetrapeptide appears as one of multiple peptide-listed ingredients on supplement fact panels, typically in proprietary blends where individual peptide amounts are not disclosed. No dose-ranging, pharmacokinetic, or dose-response studies for this specific tetrapeptide have been published in the peer-reviewed literature.

For context regarding its constituent amino acids, the following dosage data come from published research on the free amino acids themselves:

• Lysine: The adult requirement for lysine is approximately 30–35 mg per kilogram of body weight per day, which translates to roughly 2,100–2,450 mg daily for a 70 kg adult. The World Health Organization (WHO) sets the requirement at 30 mg/kg/day.
• Glycine: Current conclusions cannot extend beyond a dose of 15 g of glycine per day, which is the highest dose well tolerated in adult humans.
• Valine: As a BCAA, valine is typically studied in combination with leucine and isoleucine. No isolated dosage recommendation for supplemental valine in humans has been established with robust clinical evidence, given that no such data exists for the anabolic efficacy of valine alone.

The significant challenges hindering translation of bioactive peptides to commercial products are their inherent drawbacks (including toxicity, bitterness, instability, and susceptibility to enzymatic degradation in the gastrointestinal tract), regulatory obstacles, and higher production costs.

9. Safety Considerations and Interactions

No human safety data are available specifically for glycyl-alanyl-lysine-L-valine. The following safety-relevant facts apply to the broader context of bioactive peptides and to the ingredient's constituent amino acids.

9.1 General Safety of Bioactive Peptides

Since they are isolated from food proteins, most food-derived peptides are considered safe and insignificantly toxic, but this concept is still a mystery, and available evidence of their safety is scarce. Some peptides may induce toxicity and allergenicity to a certain degree.

Uniform quality, high cost, poor sensory acceptance, lack of toxicological studies and clinical evidence, paltry stability, and lack of bioavailability data are some of the key challenges hindering commercial advancement of bioactive peptide-based functional foods. Absorption, distribution, metabolism and excretion (ADME) studies in rodents, in vitro genotoxicity, and immunogenicity data could be considered as absolute prerequisites to ensure safety of bioactive peptides. In the absence of ADME and genotoxicity data, long-term usage to evaluate safety is highly warranted.

Upon administration into the human body, peptides may be susceptible to inactivation due to the concentration of salts and serum binding, limiting their thorough clinical transformation into novel drugs.

9.2 Stability and Enzymatic Degradation

Tetrapeptide stability and bioavailability are influenced by metabolic stability and the ability to cross the blood-brain barrier. The blood-brain barrier contains proteolytic enzymes, including aminopeptidase A, aminopeptidase M, and ACE, which degrade peptides and limit their bioavailability. This means that even if any intact tetrapeptide were to reach systemic circulation, degradation by circulating and tissue-bound peptidases would further limit its half-life and distribution.

9.3 Allergenicity

Since food-derived bioactive peptides are generally considered safe, available evidence of their safety is scarce. Some peptides may induce toxicity and allergenicity to a certain degree. Individuals with known protein allergies—particularly those related to the protein sources from which such synthetic peptides are manufactured—should consider potential allergenic cross-reactivity, though no specific allergenicity data for glycyl-alanyl-lysine-L-valine have been published.

9.4 Regulatory Status

Countries like Canada and the United States do not provide any legal status for "functional food." Although the bioactivity of peptides has been widely proved in vitro or in animal experiments, the lack of clinical trials is the biggest obstacle to their development. When bioactive peptides are put into the market as functional food or healthy food, it is necessary to determine their safety and efficacy. Moreover, different countries have strict regulatory requirements for functional food, which vary with each other, but the health declaration of functional food is essential.

In the United States, synthetic peptides such as glycyl-alanyl-lysine-L-valine used as dietary supplement ingredients are regulated under the Dietary Supplement Health and Education Act (DSHEA, 1994) by the FDA. Manufacturers bear the responsibility of establishing safety; no pre-market approval is required. No specific FDA GRAS (Generally Recognized As Safe) notice or New Dietary Ingredient (NDI) notification for this exact tetrapeptide has been identified in publicly accessible FDA databases at the time of writing.

9.5 Potential Drug and Nutrient Interactions

No interactions between glycyl-alanyl-lysine-L-valine and pharmaceutical agents have been characterized in the published literature. Given that lysine is a constituent, the well-characterized competitive relationship between lysine and arginine at the level of intestinal absorption is relevant: lysine and arginine share a cationic amino acid transporter (CAT), such that high lysine intake can reduce arginine absorption and vice versa. Lysine shares a metabolic antagonism with arginine, which makes lysine particularly interesting for herpes virus prevention. This interaction would only be relevant if meaningful amounts of free lysine were liberated from the tetrapeptide upon digestion.

10. Evidence Strength Summary

• Glycyl-alanyl-lysine-L-valine as a discrete tetrapeptide: No peer-reviewed human clinical trials. No published animal studies specific to this sequence. No established dosage, pharmacokinetic profile, or safety data. Evidence level: absent / preclinical analogy only.
• Class evidence (bioactive tetrapeptides and related oligopeptides): Limited. Although the bioactivity of peptides has been widely proved in vitro or in animal experiments, the lack of clinical trials is the biggest obstacle to development. Evidence level: primarily in vitro and animal; insufficient for human health claims.
• Constituent amino acids (glycine, alanine, lysine, valine): Each has a substantial and independent evidence base relating to core metabolic and physiological roles. However, this evidence pertains to the free amino acids, not to peptide-bound forms in this specific sequence. Evidence level for constituents: moderate to strong for established physiological roles; does not transfer to the intact tetrapeptide.

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