If you have been reading about cyclic heptapeptide and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-03-07. Where a claim depends on a specific study, the study is described rather than over-claimed.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence incorporates a lactam bridge that constrains the peptide into a ring, which increases resistance to enzymatic breakdown relative to the natural hormone. Researchers at the University of Arizona synthesised the compound in the late 1980s and early 1990s while studying pigmentation pathways. It has never received marketing approval from any national medicines regulator. In the scientific literature it is usually described as a laboratory research reagent rather than a therapeutic product.
The peptide acts as a non-selective agonist at melanocortin receptors, showing affinity for MC1R, MC3R, MC4R and MC5R. Activation of MC1R on melanocytes drives the conversion of tyrosine into melanin and shifts production toward the darker eumelanin form. MC4R signalling in the central nervous system is linked to appetite and energy balance, which helps explain why reduced food intake appeared in early human studies. Effects on MC4R and on vascular tone also account for the erectile responses recorded as unexpected findings in those same trials.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Alpha-MSH analogue with a lactam ring |
| Molecular formula | C50H69N15O9 | Commonly cited value for the neutral peptide |
| Molecular weight | 1024.18 g/mol | Calculated for the free molecule |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water, DMSO and ethanol | Dissolution in pure water is often slow |
The compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
Early published reports described melanotan-2 as a tanning agent without sun protection, which means darkening is not the same as protection against ultraviolet radiation. Later studies explored the peptide in erectile dysfunction, hemorrhagic shock, and some skin conditions. No regulator in the United States or Europe has approved it for clinical use. Many products labelled melanotan-2 are sold without approval and their identity and purity are unverified. Its long-term safety in humans remains an open question.
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
each holding with equality only when a = b = c. This says that in the non-equilateral case the harmonic mean of the sides is less than their geometric mean, which in turn is less than their arithmetic mean, and which in turn is less than their quadratic mean.
replication fork Also Y fork. The point at which the paired strands of a double-stranded DNA molecule are separated by helicase during DNA replication, breaking the hydrogen bonds between the complementary strands and thereby forming a structure with two branching single strands of DNA. Once unpaired, these strands serve as templates from which DNA polymerase synthesizes the leading strand and lagging strand. As replication proceeds, helicase moves along the DNA and continues to separate the strands, causing the replication fork to move as well. A pair of replication forks forms when helicases work in opposite directions from a single origin of replication, creating a replication eye.
==== Earthquakes ==== Some monitoring stations have reported that earthquakes are sometimes preceded by a spike in ultra-low-frequency (ULF) activity. A notable example of this occurred before the 1989 Loma Prieta earthquake in California, although a subsequent study indicated that this was little more than a sensor malfunction. On December 9, 2010, geoscientists announced that the DEMETER satellite observed a dramatic increase in ULF radio waves over Haiti in the month before the magnitude 7.0 Mw 2010 earthquake. Researchers are attempting to learn more about this correlation to determine whether this method can be used as part of an earthquake early warning system.
=== 17 June === Ukraine launched a drone attack on western Russia, with the HUR claiming to have struck a metallurgical plant and military production facilities in Belgorod, Voronezh, and Lipetsk Oblasts. The Russian Investigative Committee charged Ukrainian Colonel Mykola Dzyaman with terrorism in absentia and placed him on a wanted list for ordering the shooting down of a A-50U over the Sea of Azov on 23 February 2024.
Sources: en.wikipedia.org
is the compartment used for the individuals of the population who have been infected and then removed from the disease, either due to immunization or due to death. Those in this category are not able to be infected again or to transmit the infection to others. The flow of this model may be considered as follows:
== Life == Sun Yaoting was born in a village near Tianjin, about 60 miles southeast of Beijing. Born into poverty, his father was a jianbing peddler. When he was young, his family's home was burned down and their fields were stolen by a landlord in their village. Inspired by an older eunuch from his village who had become rich, coupled with the family's hope that they would gain Imperial influence and get revenge on the landlord, the family decided to emasculate Sun. In 1911, at the age of eight, Sun was emasculated by his father at home on their bed with a single razor cut, without the use of anesthesia. A piece of oil-soaked paper was used as a bandage, while a goose quill was inserted in Sun's urethra to prevent it from getting blocked as the wound healed. Sun remained unconscious for three days and could barely move for two months. However, the emperor he had hoped to serve, Puyi, had abdicated several weeks before his recovery during the Xinhai Revolution. Nonetheless, Sun went to Beijing at age 14. His rank initially was so low that he was not even given a name, and worked as a servant to another, higher ranking eunuch. He then rose through the ranks, becoming a palace eunuch serving under one of the emperor’s uncles, eventually becoming an attendant to the Qing empress. Corruption amongs the eunuchs working in the Forbidden City was rampant, as they constantly stole treasures and sold it on the black market.
Microfluidic liquid-liquid extraction has shown to be advantageous in numerous applications such as pharmacokinetic drug studies where only small cell numbers are needed, and in additional studies where smaller reagent volumes are required. Droplet-based microfluidics can also be used for chemical phase transfer reactions. An early example was the synthesis of azo dyes in nanoliter fluid segments using a double injector chip device.
== Pharmacodynamics == The principal mechanism of action for ethanol has proven elusive and remains not fully understood. Identifying molecular targets for ethanol is unusually difficult, in large part due to its unique biochemical properties. Specifically, ethanol is a very low molecular weight compound and is of exceptionally low potency in its actions, causing effects only at very high (millimolar mM) concentrations. For these reasons, it is not possible to employ traditional biochemical techniques to directly assess the binding of ethanol to receptors or ion channels. Instead, researchers have had to rely on functional studies to elucidate the actions of ethanol. Even at present, no binding sites have been unambiguously identified and established for ethanol. Studies have published strong evidence for certain functions of ethanol in specific systems, but other laboratories have found that these findings do not replicate with different neuronal types and heterologously expressed receptors. Thus, there remains lingering doubt about the mechanisms of ethanol listed here, even for the GABAA receptor, the most-studied mechanism. In the past, alcohol was believed to be a non-specific pharmacological agent affecting many neurotransmitter systems in the brain, but progress has been made over the last few decades. It appears that it affects ion channels, in particular ligand-gated ion channels, to mediate its effects in the CNS. In some systems, these effects are facilitatory, and in others inhibitory.
Proteins are essential nutrients for the human body. They are one of the constituents of body tissue and also serve as a fuel source. As fuel, proteins have the same energy density as carbohydrates: 17 kJ (4 kcal) per gram. From a nutritional perspective, the defining characteristic of protein is its amino acid composition. Protein content in foods is commonly measured based on nitrogen content, as nitrogen is a fundamental component of amino acids. Proteins are polymer chains made of amino acids linked by peptide bonds. During human digestion, proteins are broken down in the stomach into smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body. There are nine essential amino acids that humans cannot biosynthesize and thus must obtain from their diet to prevent protein-energy malnutrition and resulting death. They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. There has been debate as to whether there are eight or nine essential amino acids. The consensus seems to lean toward nine since histidine is not synthesized in adults. There are five amino acids that the human body can synthesize: alanine, aspartic acid, asparagine, glutamic acid and serine.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide modelled on alpha-melanocyte-stimulating hormone. A lactam bridge links two side chains, forming a ring that stabilises the molecule against proteolysis. It belongs to the broader melanocortin peptide family.
No national medicines agency has approved melanotan-2 for clinical use. Afamelanotide, a related but distinct peptide, holds a marketing authorisation in the European Union for a rare photosensitivity disorder. Melanotan-2 itself is handled as a laboratory chemical.
Its broad activity across melanocortin receptors makes it a tool for probing pigmentation, appetite and vascular signalling. Early trials recorded skin darkening and other effects that were not the original focus of the work. Those observations generated hypotheses that later studies have examined.
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.