cyclic heptapeptide comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2025-07-23. Where a claim depends on a specific study, the study is described rather than over-claimed.
The peptide was developed during the 1980s by researchers investigating melanocortin signalling and skin pigmentation pathways. Early work focused on analogues of alpha-melanocyte-stimulating hormone that would resist enzymatic breakdown more effectively than the parent molecule. Melanotan-2 emerged from that programme as a shortened, cyclised variant. Reports describing its synthesis and receptor activity later appeared in the scientific literature. Commercial availability grew through unregulated channels rather than through pharmaceutical approval.
Structurally, Melanotan-2 retains the core recognition motif of alpha-melanocyte-stimulating hormone while adding a lactam bridge that links two side chains and constrains the molecule into a ring. This modification lowers susceptibility to enzymatic degradation. The compound acts as an agonist at melanocortin receptors, particularly subtypes associated with melanin production. Because the same receptor family influences several physiological processes, researchers note that its activity is not confined to pigmentation alone. Receptor selectivity continues to be examined in published studies.
Melanocortin receptors comprise five subtypes with distinct tissue distributions and functions. Melanotan-2 is described in the literature as a non-selective agonist that engages several of these subtypes, including MC1R, MC3R, MC4R, and MC5R. MC1R is the subtype most directly linked to melanin production in skin cells. Because the compound is not subtype-selective, its observed effects in experimental settings are generally attributed to activity across multiple receptor pathways rather than to a single target.
Melanotan-2 is a synthetic linear peptide built from seven amino acids arranged in a short chain. Its sequence is commonly written as Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-NH2, which includes a modified N-terminus and an amidated C-terminus. The molecule belongs to the melanocortin family and acts as a receptor agonist. Structural features such as the D-phenylalanine residue and the Nle substitution are associated with increased stability against enzymatic degradation relative to the natural parent peptide.
The compound emerged from research programs in the 1980s that examined analogues of alpha-melanocyte-stimulating hormone for pigmentation and photoprotection. Investigators modified the native sequence to extend activity duration and potency. A related analogue, afamelanotide, was developed within the same broad line of inquiry and eventually gained approval in certain jurisdictions for a rare light-sensitivity condition. Melanotan-2 itself did not progress through the same regulatory route and has no approved therapeutic indication.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Synthetic cyclic heptapeptide |
| Molecular mass | Approximately 1024 g/mol | Depends on counter-ion content |
| Appearance | White to off-white powder | Commonly supplied as a lyophilised solid |
| Solubility | Freely soluble in water | Also dissolves in common aqueous buffers |
| Typical storage | -20 degrees Celsius, desiccated | Protect from light and repeated freeze-thaw |
Activity is attributed to agonism at melanocortin receptors, particularly MC1R and MC4R. Activation of MC1R on melanocytes increases melanin synthesis, which underlies the reported tanning effect. MC4R engagement in the central nervous system is linked to appetite suppression and to effects on sexual arousal reported in early clinical studies. Those studies were small and were not designed to establish efficacy or long-term safety. Receptor selectivity among the melanocortin subtypes is not absolute, which complicates attribution of any effect to a single pathway.
Regulatory treatment varies between countries. Several national medicines agencies have classified the peptide as unapproved, and customs authorities in some jurisdictions seize shipments on that basis. A few jurisdictions channel supply through prescription-only frameworks that do not list the substance by name. Because the material circulates mainly through online vendors, composition and purity are rarely verified before sale. Surveys of unapproved peptide products have reported labels that did not match measured content in a substantial fraction of samples.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
Receptor-binding studies classify melanotan II as a non-selective melanocortin agonist. It interacts with MC1R, MC3R, MC4R and MC5R, with reported affinities in the low nanomolar range and no strong subtype preference. Activation of MC1R on dermal melanocytes shifts pigment synthesis toward eumelanin, the dark polymer deposited in melanosomes and transferred to keratinocytes. Because the same peptide engages MC4R in the hypothalamus, it also appears in animal work on food intake and erectile response, which is why it is discussed in both pigment and metabolic research. Which receptor populations dominate after systemic exposure in humans is not fully established.
== B == Babinski sign A reflex where the big toe extends upward and the other toes fan out when the sole of the foot is stimulated. Present in infants, but indicative of damage to the corticospinal tract in adults. Barrel cortex A region of the somatosensory cortex in rodents that contains clusters of neurons corresponding to individual whiskers, used as a model for studying sensory processing and plasticity. Baroreceptor A sensory nerve ending in blood vessels that detects changes in blood pressure and relays information to the brainstem for autonomic regulation. Basal ganglia A group of subcortical nuclei involved in motor control, procedural learning, routine behaviors or "habits", and cognition. Dysfunction is associated with Parkinson’s disease, Huntington’s disease, and other movement disorders. Behavioral neuroscience A subfield of neuroscience that explores how the brain affects behavior, often using techniques from biology, psychology, and physiology. Beta wave A type of brain wave oscillation in the frequency range of approximately 13–30 Hz, typically associated with active concentration, alertness, and cognitive engagement. Bilateral In neuroscience, refers to structures or functions that involve both sides of the brain or body. For example, bilateral activation may occur in both hemispheres during a cognitive task. Binocular rivalry A phenomenon that occurs when two different images are presented to each eye, and perception alternates between them. It is used to study visual awareness and consciousness.
==== Other consequences ==== In contrast to adults, excessive daytime sleepiness (EDS) is not the most commonly reported symptoms in children with OSA. However, using objective questionnaires, it is possible to notice that the frequency of EDS in children is higher than what is reported by the parents or caretakers (40–50%). And the risk for EDS is even increased when OSA is associated with obesity. Due to the consequences and symptoms it generates, OSA in children leads to a significant decrease in quality of life, the decrease being even higher when obesity is present. The quality of life can however be improved with the treatment of OSA. SDB have also been linked to a higher rate of internalizing disorders such as anxiety and depression. Indeed, depressive symptoms have shown to be higher in children with OSA, especially in males. Once again, the severity of depressive symptoms is positively correlated with the severity of the SDB. It also interacts with obesity as obese children have higher risk to show depressive symptoms and obesity can cause OSA. The link can also go the other way around with the depression inducing obesity (due to overeating) which worsens the OSA. Adenotonsillectomy can decrease the intensity of the depressive symptoms. Other consequences of a disturbed sleep in children with OSA comprise anhedonia increased fatigue and decreased interest in daily activities, which in turn can affect the child's social relationships.
Iso-LSD, also known as d-iso-LSD, (+)-iso-LSD, or (5R-8S)-LSD, as well as N,N-diethylisolysergamide, is a serotonin receptor modulator of the lysergamide family related to lysergic acid diethylamide (LSD). It is the 8-position epimer of LSD, with iso-LSD being 8α (8S) and LSD being 8β (8R). Iso-LSD is also the N,N-diethyl derivative of isoergine (isolysergic acid amide; iso-LSA), a constituent found in morning glory seeds. Iso-LSD is one of four possible stereoisomers of LSD.
Less common but more accurate and reliable is a molecular-mass-sensitive detector using multi-angle laser-light scattering - see static light scattering. These detectors directly measure the molecular mass of the polymer and are most often used in conjunction with differential refractive index detectors. A further alternative is either low-angle light scattering, which uses a single low angle to determine the molar mass, or Right-angle-light laser scattering in combination with a viscometer, although this latter technique does not give an absolute measure of molar mass but one relative to the structural model used. The molar mass distribution of a polymer sample depends on factors such as chemical kinetics and work-up procedure. Ideal step-growth polymerization gives a polymer with dispersity of 2. Ideal living polymerization results in a dispersity of 1. By dissolving a polymer an insoluble high molar mass fraction may be filtered off resulting in a large reduction in Mw and a small reduction in Mn, thus reducing dispersity.
== Use == While originally invented as a tool to help university librarians to decide which journals to purchase, the impact factor soon became used as a measure for judging academic success. This use of impact factors was summarised by Hoeffel in 1998:
Sources: en.wikipedia.org
Like leptin, observations in both humans and animal models have shown that adiponectin is relevant to insulin sensitivity and energy homeostasis. In contrast, the relationship between resistin and adiposity is not consistent between rodent models and human subjects (See Peter Arner, 2005: "Resistin: yet another adipokine tells us that men are not mice"); hence, the notion of resistin as a genuine adipose-derived hormone remains questionable.
Taihō had just launched 42 aircraft as a part of the second raid when Albacore fired the torpedo spread. Of the six torpedoes fired, four veered off-target. Japanese pilot Sakio Komatsu had recently launched and from his aircraft sighted one of the two torpedoes which were heading for Taihō. Komatsu dived into the path of the torpedo which then detonated. The sixth torpedo struck the carrier on her starboard side and ruptured two aviation fuel tanks. The carrier's escorting destroyers made depth charge attacks but caused only minor damage to Albacore. Initially, the damage to Taihō seemed minor; the flooding was quickly contained and the carrier's propulsion and navigation were unaffected. Taihō quickly resumed regular operations, but gasoline vapor from the ruptured fuel tanks began to fill the hangar decks, creating an increasingly dangerous situation on board.
=== Low sulfur === The value of fuels and oils which are generated from the crude oil falls off due to its sulfur compounds. “They cause corrosion of equipment during treatment, reduce activity of antidetonation additives and antioxidizing stability of gasoline, raise the propensity to form hard residues in cracking gasoline fractions, and result and environment pollution". According to world standards, the content of sulfur in BLCO is low, so refinery infrastructure is less affected by corrosion and low impact on environment which his occurred by its byproducts. The sulfur content varies from 0.14% to 0.16%. If less than 1% of sulfur is included in crude oil, it is assorted into sweet, which means low sulfur content.
== Active site and mechanism of catalysis == The active site of eqolosin contains a distinctive glutamic acid and glutamine catalytic dyad which are involved in substrate binding and catalysis. These residues act as a nucleophile, with the glutamic acid serving as a general acid in the first phase of the reaction, donating a proton to the carbonyl oxygen in the peptide bond of the substrate. One or two water molecules may be involved in the reaction supplying a hydroxyl group, and the glutamic acid further donates a proton to the amide nitrogen, resulting in breakage of the peptide bond. The glutamine then returns the glutamic acid to its initial state.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and an analogue of alpha-melanocyte-stimulating hormone. The molecule is produced by chemical synthesis rather than extracted from a biological source.
It is shorter than the native hormone and carries a cyclic constraint that improves stability. These changes raise receptor potency and slow breakdown relative to the naturally occurring peptide.
Published accounts date its development to the 1980s, when researchers were generating analogues of melanocyte-stimulating hormone. That work aimed to produce more stable compounds for studying pigmentation biology.
No. Melanotan-2 is manufactured synthetically. The naturally occurring peptide in the same family is alpha-melanocyte-stimulating hormone, which the body produces as part of normal endocrine and neural signalling.