Everything below concerns GABA-A receptor. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Updated 2026-07-23. Numbers and descriptions here follow the published literature rather than marketing material.
Tuftsin, the parent structure, is a naturally occurring immunomodulatory tetrapeptide released from the Fc region of immunoglobulin G by spleen enzymes. Selank extends this four-residue sequence with three additional amino acids. The stated rationale is that the added tail slows enzymatic breakdown and may influence receptor interactions. How the full heptapeptide behaves at the molecular level is not firmly established, and proposed mechanisms often involve indirect modulation of neurotransmitter or immune signaling rather than a single defined target.
Selank is a synthetic heptapeptide developed in Russia. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, a seven-residue chain built around the natural tetrapeptide tuftsin. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences first described the compound in the mid-1990s. The design combined the tuftsin core with an added Pro-Gly-Pro tail, a modification intended to extend the molecule's stability in biological fluids. Published work on the peptide has appeared mainly in Russian-language journals.
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Modeled on tuftsin |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues |
| Approximate molecular mass | Around 750 Da | Depends on counter-ion and hydration |
| Common forms | Lyophilized powder | Also described as aqueous solution |
| Primary origin of research | Russian laboratories | Mid-1990s onward |
Pharmacokinetic data are sparse and largely derived from animal work. After intranasal administration the peptide appears in plasma within minutes, and reported half-lives are short, on the order of minutes to tens of minutes. Degradation proceeds through ordinary proteolytic cleavage into constituent amino acids and smaller fragments. Direct evidence that intact Selank reaches brain tissue in meaningful amounts is limited, and the extent of blood-brain barrier penetration is debated. Some authors argue that fragments, not the parent peptide, carry much of the observed activity.
Published clinical work is concentrated in Russian-language journals and generally involves small samples without independent replication. Systematic reviews in English note the shortage of randomised, placebo-controlled trials and the difficulty of verifying methods from translated reports. Outcome measures vary between studies, which complicates pooling of results. Interest in the compound as a cognitive or anxiolytic agent therefore rests on a thinner evidence base than the volume of citations suggests. Replication in well-powered trials with preregistered endpoints would be needed before firm conclusions about efficacy can be drawn.
Proposed mechanisms centre on the GABAergic system. Animal and tissue studies report changes in GABA-A receptor expression and reduced activity of GABA transaminase, the enzyme that degrades GABA. Effects on monoamine turnover, including serotonin and dopamine pathways, are also described, and a separate line of work links the peptide to increased expression of brain-derived neurotrophic factor in hippocampal tissue. Most of these findings come from rodent models and cell preparations. How the individual observations combine into a single coherent mode of action is not settled.
Naming conventions place Selank in the same research family as Semax, another Russian-developed peptide investigated for cognitive effects. The two compounds share a lineage but differ in sequence and in the biological systems proposed as their targets. Semax descends from ACTH fragments, whereas Selank descends from tuftsin. Publications sometimes identify Selank by its full peptide sequence or by laboratory codes rather than one uniform trade name. Because replication outside Russia is limited, reports on its properties are best read alongside the study design and the purity of the material tested.
Selank is a synthetic heptapeptide developed in Russia during the 1990s. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences designed it as a stabilized analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The compound has been studied primarily for its reported anxiolytic and nootropic effects. It remains largely unknown in Western pharmacology and is not approved as a medicine by major regulators such as the FDA or the EMA.
Measuring peptide exposure inside the brain is technically difficult. Selank is degraded rapidly in plasma, and assays must separate intact peptide from fragments, which favors targeted mass spectrometry over immunoassays alone. Reported half-lives are short, on the order of minutes, so effects observed hours later are attributed to downstream signaling rather than to the parent compound. Blood-brain barrier permeability is debated and rarely quantified directly. Gaps include absent dose-response characterization, inconsistent reporting of purity, and almost no pharmacokinetic data from human participants.
Selank is studied chiefly as an animal-model anxiolytic with proposed secondary effects on memory and immune signaling. Reported mechanisms include modulation of the GABA-A receptor complex, inhibition of enkephalin-degrading enzymes, and shifts in monoamine turnover within limbic structures. Some experiments describe increased expression of brain-derived neurotrophic factor in the hippocampus after repeated dosing. No single molecular target has been confirmed, and the peptide does not bind any receptor with the selectivity typical of a conventional small-molecule drug. Mechanism therefore remains a set of hypotheses rather than an established pathway.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
where γ is the gyromagnetic ratio. Classically, this corresponds to the proportionality between the angular momentum and the magnetic dipole moment of a spinning charged sphere, both of which are vectors parallel to the rotation axis whose length increases proportional to the spinning frequency. It is the magnetic moment and its interaction with magnetic fields that allows the observation of NMR signal associated with transitions between nuclear spin levels during resonant RF irradiation or caused by Larmor precession of the average magnetic moment after resonant irradiation. Nuclides with even numbers of both protons and neutrons have zero nuclear magnetic dipole moment and hence do not exhibit NMR signal. For instance, 18O is an example of a nuclide that produces no NMR signal, whereas 13C, 31P, 35Cl and 37Cl are nuclides that do exhibit NMR spectra. The last two nuclei have spin S > 1/2 and are therefore quadrupolar nuclei. Electron spin resonance (ESR) is a related technique in which transitions between electronic rather than nuclear spin levels are detected. The basic principles are similar but the instrumentation, data analysis, and detailed theory are significantly different. Moreover, there is a much smaller number of molecules and materials with unpaired electron spins that exhibit ESR (or electron paramagnetic resonance (EPR)) absorption than those that have NMR absorption spectra. On the other hand, ESR has much higher signal per spin than NMR does.
Long-chain-fatty-acid—CoA ligase catalyzes the reaction between a fatty acid with ATP to give a fatty acyl adenylate, plus inorganic pyrophosphate, which then reacts with free coenzyme A to give a fatty acyl-CoA ester and AMP. If the fatty acyl-CoA has a long chain, then the carnitine shuttle must be utilized (shown in the table below): Acyl-CoA is transferred to the hydroxyl group of carnitine by carnitine palmitoyltransferase I, located on the cytosolic faces of the outer and inner mitochondrial membranes. Acyl-carnitine is shuttled inside by a carnitine-acylcarnitine translocase, as a carnitine is shuttled outside. Acyl-carnitine is converted back to acyl-CoA by carnitine palmitoyltransferase II, located on the interior face of the inner mitochondrial membrane. The liberated carnitine is shuttled back to the cytosol, as an acyl-carnitine is shuttled into the matrix. If the fatty acyl-CoA contains a short chain, these short-chain fatty acids can simply diffuse through the inner mitochondrial membrane.
==== Economic issues ==== In 2010, Larson introduced the Small Business Jobs Act of 2010, authorizing the creation of the Small Business Lending Fund Program administered by the Treasury Department to make capital investments in eligible institutions, in order to increase the availability of credit for small businesses. Larson was a strong advocate for the American Recovery and Reinvestment Act of 2009, which increased federal spending in infrastructure, education, health and energy while expanding some welfare and social security programs. His liberal stance on government spending has earned him a rating of 9% with Citizens Against Government Waste, a conservative anti-government spending interest group.
2.A.1 Major Facilitator superfamily (MFS), see also Lactose permease, Phosphate permease and Glucose transporter 2.A.2 The Glycoside-Pentoside-Hexuronide (GPH):Cation Symporter Family 2.A.3 The Amino Acid-Polyamine-Organocation (APC) Family 2.A.4 Cation diffusion facilitator (CDF) Family 2.A.5 Zinc (Zn2+)-Iron (Fe2+) Permease Family 2.A.6 Resistance-Nodulation-Cell Division Superfamily, see also SecDF protein-export membrane protein 2.A.7 The Drug/Metabolite Transporter (DMT) Superfamily 2.A.8 The Gluconate:H+ Symporter (GntP) Family 2.A.9 The Membrane Protein Insertase (YidC/Alb3/Oxa1) Family 2.A.10 The 2-Keto-3-Deoxygluconate Transporter (KdgT) Family 2.A.11 The Citrate-Mg2+:H+ (CitM) Citrate-Ca2+:H+ (CitH) Symporter (CitMHS) Family 2.A.12 ATP:ADP Antiporter Family 2.A.13 The C4-Dicarboxylate Uptake (Dcu) Family 2.A.14 Lactate Permease Family 2.A.15 The Betaine/Carnitine/Choline Transporter (BCCT) Family 2.A.16 Tellurite-resistance/Dicarboxylate Transporter Family 2.A.17 Proton-dependent Oligopeptide Transporter Family 2.A.18 The Amino Acid/Auxin Permease (AAAP) Family 2.A.19 The Ca2+:Cation Antiporter (CaCA) Family 2.A.20 The Inorganic Phosphate Transporter (PiT) Family 2.A.21 Solute:Sodium Symporter Family 2.A.22 The Neurotransmitter:Sodium Symporter Family 2.A.23 The Dicarboxylate/Amino Acid:Cation (Na+ or H+) Symporter (DAACS) Family 2.A.24 The 2-Hydroxycarboxylate Transporter (2-HCT) Family 2.A.25 Alanine or Glycine:Cation Symporter (AGCS) Family 2.A.26 The Branched Chain Amino Acid:Cation Symporter (LIVCS) Family 2.A.27 The Glutamate:Na+ Symporter (ESS) Family 2.A.28 Bile Acid:Na+ Symporter Family 2.A.29 Mitochondrial carrier Family 2.A.30 Cation-Chloride Cotransporter (CCC) Family 2.A.31 Anion Exchanger Family 2.A.32 The Silicon Transporter (Sit) Family 2.A.33 NhaA Na+:H+ Antiporter (NhaA) Family 2.A.34 The NhaB Na+:H+ Antiporter (NhaB) Family 2.A.35 The NhaC Na+:H+ Antiporter (NhaC) Family 2.A.36 Monovalent Cation:Proton Antiporter-1 (CPA1) Family 2.A.37 Monovalent Cation:Proton Antiporter-2 (CPA2) Family 2.A.38 K+ Transporter (Trk) Family 2.A.39 Nucleobase:Cation Symporter-1 (NCS1) Family 2.A.40 Nucleobase:Cation Symporter-2 (NCS2) Family 2.A.41 The Concentrative Nucleoside Transporter (CNT) Family 2.A.42 The Hydroxy/Aromatic Amino Acid Permease (HAAAP) Family 2.A.43 The Lysosomal Cystine Transporter (LCT) Family 2.A.45 Arsenite-Antimonite Efflux Family 2.A.46 The Benzoate:H+ Symporter (BenE) Family 2.A.47 Divalent Anion:Na+ Symporter (DASS) Family 2.A.48 The Reduced Folate Carrier (RFC) Family 2.A.49 Chloride Carrier/Channel (ClC) Family 2.A.50 The Glycerol Uptake (GUP) Family 2.A.51 The Chromate Ion Transporter (CHR) Family 2.A.52 The Ni2+-Co2+ Transporter (NiCoT) Family 2.A.53 Sulfate permease (SulP) Family 2.A.54 The Mitochondrial Tricarboxylate Carrier (MTC) Family 2.A.55 The Metal Ion (Mn2+-iron) Transporter (Nramp) Family 2.A.56 The Tripartite ATP-independent Periplasmic Transporter (TRAP-T) Family 2.A.57 The Equilibrative Nucleoside Transporter (ENT) Family 2.A.58 The Phosphate:Na+ Symporter (PNaS) Family 2.A.59 The Arsenical Resistance-3 (ACR3) Family 2.A.60 Organo Anion Transporter (OAT) Family 2.A.61 The C4-dicarboxylate Uptake C (DcuC) Family 2.A.62 The NhaD Na+:H+ Antiporter (NhaD) Family 2.A.63 The Monovalent Cation (K+ or Na+):Proton Antiporter-3 (CPA3) Family 2.A.64 Twin Arginine Targeting (Tat) Family 2.A.65 The Bilirubin Transporter (BRT) Family 2.A.66 The Multidrug/Oligosaccharidyl-lipid/Polysaccharide (MOP) Flippase Superfamily 2.A.67 The Oligopeptide Transporter (OPT) Family 2.A.68 The p-Aminobenzoyl-glutamate Transporter (AbgT) Family 2.A.69 The Auxin Efflux Carrier (AEC) Family 2.A.70 The Malonate:Na+ Symporter (MSS) Family 2.A.71 The Folate-Biopterin Transporter (FBT) Family 2.A.72 The K+ Uptake Permease (KUP) Family 2.A.73 The Short Chain Fatty Acid Uptake (AtoE) Family 2.A.74 The 4 TMS Multidrug Endosomal Transporter (MET) Family 2.A.75 The L-Lysine Exporter (LysE) Family 2.A.76 The Resistance to Homoserine/Threonine (RhtB) Family 2.A.77 The Cadmium Resistance (CadD) Family 2.A.78 The Branched Chain Amino Acid Exporter (LIV-E) Family 2.A.79 The Threonine/Serine Exporter (ThrE) Family 2.A.80 The Tricarboxylate Transporter (TTT) Family 2.A.81 The Aspartate:Alanine Exchanger (AAEx) Family 2.A.82 The Organic Solute Transporter (OST) Family 2.A.83 The Na+-dependent Bicarbonate Transporter (SBT) Family 2.A.84 The Chloroplast Maltose Exporter (MEX) Family 2.A.85 The Aromatic Acid Exporter (ArAE) Family 2.A.86 The Autoinducer-2 Exporter (AI-2E) Family (Formerly the PerM Family, TC #9.B.22) 2.A.87 The Prokaryotic Riboflavin Transporter (P-RFT) Family 2.A.88 Vitamin Uptake Transporter (VUT or ECF) Family 2.A.89 The Vacuolar Iron Transporter (VIT) Family 2.A.90 Vitamin A Receptor/Transporter (STRA6) Family 2.A.91 Mitochondrial tRNA Import Complex (M-RIC) (Formerly 9.C.8) 2.A.92 The Choline Transporter-like (CTL) Family 2.A.94 The Phosphate Permease (Pho1) Family 2.A.95 The 6TMS Neutral Amino Acid Transporter (NAAT) Family 2.A.96 The Acetate Uptake Transporter (AceTr) Family 2.A.97 The Mitochondrial Inner Membrane K+/H+ and Ca2+/H+ Exchanger (LetM1) Family 2.A.98 The Putative Sulfate Exporter (PSE) Family 2.A.99 The 6TMS Ni2+ uptake transporter (HupE-UreJ) Family 2.A.100 The Ferroportin (Fpn) Family 2.A.101 The Malonate Uptake (MatC) Family (Formerly UIT1) 2.A.102 The 4-Toluene Sulfonate Uptake Permease (TSUP) Family 2.A.103 The Bacterial Murein Precursor Exporter (MPE) Family 2.A.104 The L-Alanine Exporter (AlaE) Family 2.A.105 The Mitochondrial Pyruvate Carrier (MPC) Family 2.A.106 The Ca2+:H+ Antiporter-2 (CaCA2) Family 2.A.107 The MntP Mn2+ Exporter (MntP) Family 2.A.108 The Iron/Lead Transporter (ILT) Family 2.A.109 The Tellurium Ion Resistance (TerC) Family 2.A.110 The Heme Transporter, heme-responsive gene protein (HRG) Family 2.A.111 The Na+/H+ Antiporter-E (NhaE) Family 2.A.112 The KX Blood-group Antigen (KXA) Family 2.A.113 The Nickel/cobalt Transporter (NicO) Family 2.A.114 The Putative Peptide Transporter Carbon Starvation CstA (CstA) Family 2.A.115 The Novobiocin Exporter (NbcE) Family 2.A.116 The Peptidoglycolipid Addressing Protein (GAP) Family 2.A.117 The Chlorhexadine Exporter (CHX) family 2.A.118 The Basic Amino Acid Antiporter (ArcD) Family 2.A.119 The Organo-Arsenical Exporter (ArsP) Family 2.A.120 The Putative Amino Acid Permease (PAAP) Family 2.A.121 The Sulfate Transporter (CysZ) Family 2.A.122 The LrgB/CidB holin-like auxiliary protein (LrgB/CidB) Family 2.A.123 The Sweet; PQ-loop; Saliva; MtN3 (Sweet) Family 2.A.124 The Lysine Exporter (LysO) Family 2.A.125 The Eukaryotic Riboflavin Transporter (E-RFT) Family 2.A.126 The Fatty Acid Exporter (FAX) Family 2.A.127 Enterobacterial Cardiolipin Transporter (CLT) Family
== Toxicity == The neurotoxicity of MCD peptide is distincted from its histamine releasing function. The histamine releasing function of MCD peptide, at low concentrations, causes the degranulation of mast cell , and shows anti-inflammatory activity at higher concentrations. These actions of MCD peptide on mast cells is thought to be involved in allergic and inflammatory processes related to type I hypersensitivity reaction. MCD peptide shows neurotoxicity by inducing epileptiform seizures in rat, when intraventricularly injected. This toxicity is caused by the blockage of voltage-gated potassium channels by the MCD peptide. However, there is no toxicity of MCD administered peripherally, even at high doses.
Sources: en.wikipedia.org
Yeast, most commonly S. cerevisiae, is used in baking as a leavening agent, converting the fermentable sugars present in dough into carbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets "set", giving the baked product a soft and spongy texture. The use of potatoes, water from potato boiling, eggs, or sugar in a bread dough accelerates the growth of yeast. Most yeasts used in baking are of the same species common in alcoholic fermentation. In addition, Saccharomyces exiguus (also known as S. minor), a wild yeast found on plants, fruits, and grains, is occasionally used for baking. In breadmaking, the yeast initially respires aerobically, producing carbon dioxide and water. When the oxygen is depleted, fermentation begins, producing ethanol as a waste product; however, this evaporates during baking.
== Geological evidence == In 2025, researchers from Johannes Gutenberg University Mainz reported unusual micro-burrows discovered in marble and limestone formations across desert regions of Namibia, Oman, and Saudi Arabia. These micro-tunnels, roughly half a millimeter wide and up to three centimeters long, were aligned vertically in parallel bands and filled with calcium carbonate powder. Traces of biological material suggest these features were formed by a previously unknown endolithic microorganism capable of penetrating deep into rock, likely to access nutrients. While no DNA was recovered, the structures are estimated to be between one and two million years old and represent possible subfossil evidence of microbial life.
dysplasia The abnormal growth or development of a tissue or organ; a change in the growth, behavior, or organization of cells within a tissue, or the presence of cells of an abnormal type, such that the tissue becomes disordered, an event which often precedes the development of cancer.
L-tyrosine → para-tyramine or L-DOPA → Dopamine L-tyrosine → L-DOPA → 3,4-dihydroxyphenylacetaldehyde (DOPAL) Dopamine + DOPAL → (S)-norlaudanosoline →→→ (S)-reticuline → 1,2-dehydroreticulinium → (R)-reticuline → salutaridine → salutaridinol → thebaine → neopinone → codeinone → codeine → morphine The intermediate (S)-norlaudanosoline (also known as tetrahydropapaveroline) is synthesized through the addition of DOPAL and dopamine. CYP2D6, a cytochrome P450 isoenzyme is involved in two steps along the biosynthetic pathway, catalyzing both the biosynthesis of dopamine from tyramine and of morphine from codeine. Urinary concentrations of endogenous codeine and morphine have been found to significantly increase in individuals taking L-DOPA for the treatment of Parkinson's disease.
Sources: en.wikipedia.org
=== Function in pregnancy === Progesterone plays a crucial role in pregnancy by supporting fetal development and maintaining the pregnancy. It is involved in the menstrual cycle, implantation, and is required for pregnancy maintenance. During implantation, it plays a role in its preservation through modulating the maternal immune response and suppressing the inflammatory response. By decreasing the maternal immune response, progesterone can allow the pregnancy to be accepted. Progesterone prepares the endometrium for implantation, as the level of progesterone increases, the capillaries grow. These capillaries spread throughout the granulosa layer of cells which promotes vascularization and blood flow in the endometrium, ensuring an adequate blood supply to the developing placenta and fetus. On the other hand, when there is no pregnancy occurred, the level of progesterone will decrease, which leads to menstruation. This means that bleeding from women's menstruation is bleeding after progesterone withdrawal.
=== Hunger and satiety hormones === Unlike the surgical sleeve gastrectomy, the ESG does not appear to affect central appetite signaling through the hunger hormone, ghrelin. This is thought to be because the surgical sleeve removes the fundus, the primary site of ghrelin production, and the relatively thinner-walled fundus is avoided in the ESG for safety concerns. Furthermore, in cases where the fundus was sutured in ESG, this did not benefit weight loss outcomes.
Also, alphaproteobacteria present a potentially large source of the lipid in the rock record. It has been suggested that these organisms may be synthesizing gammacerane in response to other shifting parameters during water column stratification, as most of the bacteria that contain the ths gene thrive in dynamic environments.
In 1996, the World Health Organization (WHO) launched the EMF (ElectroMagnetic Fields) Project to bring together current knowledge and available resources from key international and national organizations and scientific institutions on electromagnetic fields. The German Federal Office for Radiation Protection (BfS) published the following recommendation in 2006:
Specially, carbon nanotubes can be transformed into sophisticated biomolecule and allow its detection through changes in the carbon nanotube fluorescence spectra. Also, carbon nanotubes can be designed to match the size of small drug and endocitozed by a target cell, hence becoming a delivery agent.
Sources: en.wikipedia.org
Selank is a synthetic peptide made of seven amino acids. It is modeled on tuftsin, a natural tetrapeptide, with an added three-residue tail. It is not a small-molecule drug.
It originates from research in Russia, associated with the Institute of Molecular Genetics of the Russian Academy of Sciences. The first descriptions date to the mid-1990s. Most published studies come from Russian laboratories.
No, Selank itself does not occur naturally. Its backbone is based on tuftsin, which is produced in the body, but the seven-residue version is a synthetic construct. It is supplied as a manufactured peptide.
It is a seven-amino-acid peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, produced by chemical synthesis rather than extracted from biological tissue. Its design is based on tuftsin, a natural immunomodulatory tetrapeptide. The C-terminal Pro-Gly-Pro segment is a common stabilising motif in short regulatory peptides.