IngredientsGlycyl-alanyl-L-isoleucine (commonly abbreviated Gly-Ala-Ile) is a synthetic tripeptide. Its full IUPAC name, as recorded in the ACD/IUPAC nomenclature system, is Glycyl-L-alanyl-L-isoleucine. Alternative systematic designations include (2S,3S)-2-((S)-2-(2-Aminoacetamido)propanamido)-3-methylpentanoic acid and the ACD Index Name L-Isoleucine, glycyl-L-alanyl-. The compound is registered under CAS Registry Number 137730-92-8.
Glycyl-alanyl-isoleucine is a tripeptide composed of glycine, alanine, and isoleucine with the molecular formula C11H21N3O4. Its molecular structure contains 11 carbon atoms, 21 hydrogen atoms, 3 nitrogen atoms, and 4 oxygen atoms. Its average mass is 259.302 Da and its monoisotopic mass is 259.153198 Da.
The tripeptide sequence proceeds N-terminal to C-terminal as glycine → alanine → isoleucine, held together by two amide (peptide) bonds. The stereospecific form referenced in dietary supplement contexts employs the naturally occurring L-stereoisomers of both alanine and isoleucine, consistent with the IUPAC name Glycyl-L-alanyl-L-isoleucine.
Glycyl-alanyl-L-isoleucine as an isolated, defined molecule is not a naturally occurring discrete entity in any botanical or animal tissue; rather, it arises transiently during the enzymatic digestion of dietary proteins in the gastrointestinal tract. All three of its constituent amino acids — glycine, L-alanine, and L-isoleucine — are themselves naturally occurring and widely distributed in animal and plant proteins.
Glycine has only a tiny hydrogen atom on its side chain and is the smallest of the twenty amino acids that build natural proteins. A typical diet contains about 2 grams of glycine daily, primarily sourced from protein-rich foods including meat, fish, and legumes.
Isoleucine, alanine's partner in this tripeptide, is a branched-chain amino acid (BCAA) and one of the nine indispensable (essential) amino acids; it cannot be synthesized by the human body and must be obtained through diet. Branched-chain amino acids — leucine, isoleucine, and valine — are essential amino acids widely studied for their crucial role in the regulation of protein synthesis, mainly through activation of the mTOR signaling pathway.
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. Short sequence tripeptides such as Gly-Ala-Ile are therefore transiently present in the intestinal lumen following the digestion of any glycine-, alanine-, and isoleucine-containing protein source — including meat, fish, dairy, eggs, soy, and legumes.
In commerce, glycyl-alanyl-L-isoleucine is available principally in two contexts:
Glycyl-alanyl-L-isoleucine as a defined chemical entity has no documented history of traditional or ethnobotanical use. It is a modern synthetic compound that did not exist in isolated form before the development of peptide chemistry in the twentieth century. No traditional medicine system — including Ayurveda, Traditional Chinese Medicine, Greco-Roman medicine, or indigenous pharmacopoeias — has knowledge of or history with this specific tripeptide. There is accordingly no traditional preparation, dose, or indication to describe.
The three constituent amino acids — glycine, L-alanine, and L-isoleucine — are, of course, intrinsic components of all protein-containing foods consumed throughout human history. However, attributing any specific traditional use to the isolated tripeptide Gly-Ala-Ile on that basis would be an unsupported extrapolation, and no such claim is made here.
Glycyl-alanyl-L-isoleucine's constituent amino acids each bring distinct biochemical properties to the tripeptide:
Glycine is the simplest proteinogenic amino acid, classified as non-essential (synthesized endogenously). It serves as a precursor for purine nucleotides, porphyrins, creatine, and bile acids, and functions as an inhibitory neurotransmitter in the brainstem and spinal cord.
L-Alanine is a non-essential glucogenic amino acid with a central role in the glucose–alanine cycle, shuttling nitrogen from muscle to liver. In a tripeptide context, alanine has been shown in preclinical research to enhance branched-chain amino acid bioavailability: the dipeptide L-alanyl-L-alanine significantly increases the absorption of BCAAs when these are administered orally and induces their preferential distribution in the muscle.
Isoleucine is an α-amino acid used in the biosynthesis of proteins. As a branched-chain amino acid (BCAA), it is essential — humans cannot synthesize it de novo. BCAAs, including isoleucine, are widely studied for their role in the regulation of protein synthesis through activation of the mTOR signaling pathway and their emerging recognition as players in glucose homeostasis. Isoleucine has been specifically identified as the BCAA most directly involved in non-insulin-dependent glucose uptake (see Section 5, below).
The tripeptide format is significant from a pharmacokinetic perspective. More than 70% of protein digestion products in the gastrointestinal tract are absorbed in the form of di/tripeptides via a specialized proton-coupled transport system. The key mediator is peptide transporter 1 (PepT1), a proton-dependent oligopeptide transporter highly expressed at the brush-border membrane of intestinal epithelial cells.
Human peptide transporter 1 (PEPT1) is an uptake transporter with a major role in the absorption of dietary di- and tripeptides from the small intestinal lumen. It is a high-capacity, low-affinity (KM of 0.2–10 mM), proton-coupled cotransporter of diverse di- and tripeptides and peptidomimetic substrates, primarily expressed on the apical microvilli of enterocytes in the small intestine, with lower expression in epithelial cells in the kidney proximal tubule.
PEPT1 accepts only dipeptides and tripeptides as substrates. Even though there are 400 different dipeptides and 8,000 different tripeptides potentially present in the intestinal lumen as the result of the digestion of dietary proteins, PEPT1 is solely responsible for handling this wide array of peptides.
Transport of di/tripeptides by PepT1 is markedly stereospecifically selective. Natural amino acids are predominantly of the L-form, and peptides composed of L-enantiomers display the highest affinity to the transporter. This is consistent with the configuration of glycyl-L-alanyl-L-isoleucine, which would be predicted to exhibit favorable PepT1 affinity relative to mixed-stereoisomer or D-amino acid-containing counterparts.
PepT1 transports bioactive di/tripeptides through a proton-coupled mechanism. The absorption of di/tripeptides relies on the alternating access transport process, and transport efficiency is influenced by peptide structure.
Important preliminary note: No published peer-reviewed human clinical trials or preclinical animal studies have been identified that investigate glycyl-alanyl-L-isoleucine (as the specific isolated tripeptide Gly-Ala-Ile) as an intervention in any health or performance outcome. Research on peptides like glycyl-alanyl-isoleucine is ongoing, but the evidence base at the level of this specific tripeptide is presently limited to its chemical characterization. What is described below represents the mechanistic and clinical evidence for its constituent amino acids and for structurally related BCAA-containing short peptides — extrapolation of which to Gly-Ala-Ile itself remains speculative.
Branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) are three of the nine indispensable amino acids and are frequently consumed as dietary supplements by athletes. 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.
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. BCAAs (leucine, isoleucine, and valine), particularly leucine, have anabolic effects on protein metabolism by increasing the rate of protein synthesis and decreasing the rate of protein degradation in resting human muscle. During recovery from endurance exercise, BCAAs were also found to have anabolic effects in human muscle. These effects are likely mediated through changes in signaling pathways involving phosphorylation of the mammalian target of rapamycin (mTOR) and sequential activation of 70-kD S6 protein kinase (p70 S6 kinase) and the eukaryotic initiation factor 4E-binding protein 1.
In a randomized, placebo-controlled human study, ten young (20.1 ± 1.3 years), resistance-trained men completed two trials, ingesting either 5.6 g BCAA or a placebo drink immediately after resistance exercise. A greater phosphorylation status of S6K1 and PRAS40 was observed in the BCAA group at 1 h post-drink ingestion. Myofibrillar-MPS was 22% higher in BCAA (0.110 ± 0.009%/h) than placebo (0.090 ± 0.006%/h). The investigators concluded that ingesting BCAAs alone increases the post-exercise stimulation of myofibrillar-MPS and phosphorylation status of mTORC1 signaling.
Whereas leucine is necessary for maximal activation of mTORC1 signaling, mTORC1 signaling is enhanced with the addition of the other two BCAAs, valine and isoleucine.
Evidence strength: For free-form BCAAs (leucine, isoleucine, valine), there is moderate-quality evidence of mTORC1 stimulation and modest effects on MPS in humans. Although BCAAs tended to activate anabolic signals, the benefits on performance and body composition were negligible in a systematic review covering 24 studies of orally supplemented athletes. No human data exist specifically for Gly-Ala-Ile.
Results from a systematic review of randomized controlled trials moderately support BCAA reducing muscle soreness; however, there is inconsistent evidence to support BCAAs having an ergogenic effect on strength and endurance.
Although BCAAs tended to activate anabolic signals, the benefits on performance and body composition were negligible. Studies that included resistance-trained participants showed that BCAAs attenuated muscle soreness after exercise, while in endurance sports the findings were inconsistent.
The protocols of BCAA supplements differed considerably between studies, and most studies did not report the total protein intake across the day; consequently, the benefits of BCAAs should be interpreted with caution.
Evidence strength: Weak-to-moderate for BCAA-related reduction of delayed-onset muscle soreness (DOMS); no specific evidence for the tripeptide Gly-Ala-Ile.
Isoleucine — the C-terminal residue of Gly-Ala-Ile — has been identified as the BCAA with the most direct insulin-independent effect on glucose uptake.
Isoleucine is a branched-chain amino acid that plays an important role in the improvement of glucose metabolism as evidenced by the increase of insulin-independent glucose uptake in vitro. In an animal study evaluating glucose uptake and oxidation in fasted rats, oral administration of isoleucine decreased the plasma glucose level by 20% and significantly increased muscle glucose uptake by 71% without significant elevation of the plasma insulin level compared with controls at 60 min after administration.
Isoleucine has been reported to participate in regulation of glucose levels in many studies. In an animal experiment, muscular GLUT and intestinal GLUT were determined in weaning pigs fed control or isoleucine-supplemented diets. Supplementation of isoleucine in the diet significantly increased piglet average daily gain, enhanced GLUT1 expression in red muscle and GLUT4 expression in red muscle, white muscle and intermediate muscle (P<0.05). Expressions of Na+/glucose co-transporter 1 and GLUT2 were also up-regulated in the small intestine when pigs were fed isoleucine-supplemented diets (P<0.05).
The proposed mechanism involves a GLUT-4-mediated pathway: in muscle cells, insulin normally binds to an insulin receptor, causing activation of phosphoinositide 3-kinase (PI3K) downstream of the insulin receptor signal, then via several signal transductions, translocates glucose transporter-4 (GLUT-4) to the surface of a cell, through which glucose is incorporated into the cell. The glucose uptake-promoting effect of isoleucine-containing peptides is suppressed by a GLUT-4 inhibitor or a PI3K inhibitor, suggesting that glucose uptake promoted by such peptides is a GLUT-4-mediated action similar to the action of insulin and also a PI3K-mediated action similar to the action of insulin.
Peptides containing isoleucine (particularly those with smaller molecular weights permitting oral absorption) have been proposed to exhibit a preventive or therapeutic effect on diabetes mellitus or on an elevation of blood glucose level, an effect on promotion of glycogen storage, or an effect on enhancement of physical strength and athletic ability. The peptide is considered as a biologically active substance with a mechanism estimated to be similar to that of insulin.
Evidence strength: Preclinical (animal and in vitro) only. No human clinical trial data exist for Gly-Ala-Ile specifically. Evidence for isoleucine's glucose-partitioning effects comes from rodent studies and cell lines. Extrapolation to the intact tripeptide requires further investigation.
There is now compelling evidence that dietary proteins are absorbed as di- and tripeptides rather than as free amino acids. This absorption process is carried out by the intestinal brush-border transporter PepT1, which transfers peptides from the intestinal lumen to the enterocyte cytoplasm.
The intestinal peptide transporter PepT1 was first identified in 1994. It plays a crucial role in the absorption of small peptides including more than 400 different dipeptides and 8,000 tripeptides digested from dietary proteins, as well as a repertoire of structurally related compounds and drugs.
From a formulation standpoint, the tripeptide structure of Gly-Ala-Ile theoretically provides it with access to this high-capacity transport route, potentially offering absorption kinetics distinct from those of the equivalent free amino acid mixture. However, oral bioavailability of bioactive di/tripeptides is limited by the complexity of intestinal absorption processes, primarily relying on PepT1 for transmembrane transport. Transport efficiency is influenced by peptide structure, meaning that the specific sequence Gly-Ala-Ile may differ in transporter affinity from other Gly- or Ile-containing tripeptides. No published pharmacokinetic study has measured plasma appearance of intact Gly-Ala-Ile in humans following oral administration.
Evidence strength: Mechanistically plausible based on established PepT1 biology, but no direct human pharmacokinetic data exist for this specific tripeptide.
Preclinical research has specifically examined whether co-administration of alanine (as part of a peptide) can potentiate the bioavailability of BCAAs. A formulation comprising BCAAs in combination with the dipeptide L-alanyl-L-alanine was found to be particularly effective in improving muscle function, structure, and metabolism — an effect observed both in intense training and in pathological conditions of muscle wasting. The dipeptide L-alanyl-L-alanine significantly increases the absorption of BCAAs when administered orally and induces their preferential distribution in the muscle. While this research pertains to alanyl-alanine rather than Gly-Ala-Ile, it supports the general concept that alanine-containing peptides may potentiate BCAA delivery.
In a murine exercise model, researchers evaluated a 4-week treatment with an oral formulation containing BCAAs alone (2:1:1 ratio) compared to three modified formulations combining BCAAs with increasing concentrations of L-alanine. A preliminary pharmacokinetic study confirmed the ability of alanine to boost up BCAAs bioavailability.
Evidence strength: Preclinical only. No clinical data exist for Gly-Ala-Ile specifically in this context.
Based on the biochemical properties of its constituent amino acids and the pharmacological literature on related peptides, glycyl-alanyl-L-isoleucine is associated with the following body systems and health areas:
No peer-reviewed human clinical trial has established or tested a dosage for glycyl-alanyl-L-isoleucine as an isolated compound. Dosage information that has appeared in publicly accessible sources is limited to commercial supplement labeling:
For context, the broader BCAA literature has used free-form BCAA doses typically ranging from approximately 5 to 20 g per day in adult humans; for example, one human randomized controlled study used 5.6 g total BCAA ingested immediately after resistance exercise. These figures pertain to free BCAAs, not to the tripeptide Gly-Ala-Ile, and cannot be directly transposed to this compound.
Glycyl-alanyl-L-isoleucine is available from chemical suppliers as a dry reagent powder for in vitro research; these products are specifically designed for in vitro studies conducted in controlled laboratory settings using cells or tissues, not for human consumption.
No dedicated toxicological studies, safety assessments, or adverse event reports for glycyl-alanyl-L-isoleucine as an isolated compound have been identified in the peer-reviewed literature or in official regulatory databases (FDA, EFSA, ECHA). The compound has not been evaluated by the European Food Safety Authority, the NIH Office of Dietary Supplements, or any pharmacopeial body as a standalone ingredient.
Short-chain peptides composed of naturally occurring amino acids, particularly those containing isoleucine, have been described in the patent literature as not exerting a harmful effect on the human body — though this characterization comes from patent claims rather than independent safety evaluation.
The constituent amino acids (glycine, L-alanine, L-isoleucine) are each generally recognized as safe (GRAS) by the FDA as food ingredients, and are present in normal dietary protein. A typical diet contains about 2 grams of glycine daily, primarily from protein-rich foods including meat, fish, and legumes. L-Isoleucine is classified as an essential amino acid and is consumed as part of normal dietary protein intake globally.
The scientific evidence base for glycyl-alanyl-L-isoleucine as a specific, isolated ingredient is extremely limited. No published peer-reviewed human clinical trials, controlled animal intervention studies, or formal safety assessments have been found for this exact tripeptide. Even for the constituent BCAAs in free form, the protocols of BCAA supplements differed considerably between studies, and most studies did not report the total protein intake across the day; consequently, any benefits must be interpreted with caution. Claims made in the sports supplement market for Gly-Ala-Ile are currently extrapolated from the free BCAA literature and from mechanistic peptide transport research, neither of which constitutes direct clinical evidence for this specific compound.
The Australian Institute of Sport has classified BCAAs in Group C, which includes supplements without scientific support among athletes or with inconclusive studies. This classification applies to free-form BCAAs; for the tripeptide form, the evidence is even more preliminary.
Health conditions that Glycyl-alanyl-L-isoleucine may help support.
Body systems that Glycyl-alanyl-L-isoleucine may help support.
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