cyclic heptapeptide is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-07-06. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Free base; salt forms differ |
| Molecular weight | Approximately 1024 g/mol | Calculated for the free base |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water and polar solvents | Poorly soluble in non-polar solvents |
| Typical storage | -20 degrees Celsius, dry, protected from light | Refers to the solid form |
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.
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.
Melanotan-2 is frequently confused with afamelanotide, a linear analogue authorised in the European Union for erythropoietic protoporphyria. The two compounds differ in chain length, ring structure and receptor selectivity, so findings for one cannot be transferred directly to the other. Published controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports. Questions about effect size, dose-response behaviour and long-term safety therefore remain unresolved.
On 5 October 2018, Singapore carried out three executions of drug traffickers - Zainudin bin Mohamed, Abdul Wahid Bin Ismail, and Mohsen Bin Na’im, it led to the Asian Forum for Human Rights and Development (FORUM-ASIA) and 28 civil society organizations in Asia showing condemnation over the triple hangings, and these groups the death sentence was a grave violation of the right to life, which was "the most fundamental and essential human right for other rights to be realized". They also argued that the executions of Zainudin, Abdul Wahid and Mohsen did not serve any purpose for the island-state and its citizens in terms of fulfilling the ends of justice. In March 2022, when Singapore dismissed the final appeal of Malaysian death row prisoner Nagaenthran K. Dharmalingam and later authorized the execution of Singaporean drug convict Abdul Kahar Othman, which was its first execution during the COVID-19 pandemic, there were 400 Singaporeans, including rights activists Jolovan Wham, Kirsten Han and Kokila Annamalai, who took part in a protest against the government's use of the death penalty at Hong Lim Park. With regards to Abdul Kahar's execution, the European Union (EU) condemned it and stated that capital punishment is a cruel and inhumane punishment, which not only failed to deter crime but also defied both humanity's dignity and integrity. Two days prior to Nagaenthran's execution (which took place on 27 April 2022), a candlelight vigil was held on his behalf.
Bioreference Laboratories, a clinical laboratory with a core genetic testing business The 4K Test Score, a blood test for prostate cancer Pharmaceutical development, with products such as Rayaldee Varubi, a chemotherapy inducted nausea medication As of 2024, the chairman and CEO of OPKO is Phillip Frost. In May 2022, OPKO Health announced the acquisition for $300 million of U.S. based Biotechnology firm, ModeX. With it OPKO gained proprietary immunotherapy technology for infectious diseases and oncology.
the hydride ion (H−), carried by NAD or NADP+ the phosphate group, carried by adenosine triphosphate the acetyl group, carried by coenzyme A formyl, methenyl or methyl groups, carried by folic acid and the methyl group, carried by S-adenosylmethionine Since coenzymes are chemically changed as a consequence of enzyme action, it is useful to consider coenzymes to be a special class of substrates, or second substrates, which are common to many different enzymes. For example, about 1000 enzymes are known to use the coenzyme NADH. Coenzymes are usually continuously regenerated and their concentrations maintained at a steady level inside the cell. For example, NADPH is regenerated through the pentose phosphate pathway and S-adenosylmethionine by methionine adenosyltransferase. This continuous regeneration means that small amounts of coenzymes can be used very intensively. For example, the human body turns over its own weight in ATP each day.
Peyronie's disease diagnosis is mostly clinical. Patient history and physical examination are crucial. The most prominent features are acquired penile curvature, palpable plaques, erectile dysfunction, and pain during erections. Penile ultrasonography is the imaging method of choice for plaque location, measurement, and confirmation of calcification. Doppler ultrasound can be utilized to assess vascular function, which is useful in the evaluation of associated erectile dysfunction. Imaging also helps to differentiate Peyronie's disease from congenital penile curvature, penile fracture, or neoplastic disease. MRI can be employed in severe ones, although it is generally not required.
Sources: en.wikipedia.org
Several diseases can affect cartilage. Chondrodystrophies are a group of diseases, characterized by the disturbance of growth and subsequent ossification of cartilage. Some common diseases that affect the cartilage are listed below.
Without strong healthy bones, humans are more at risk for different chronic diseases and fractures, with day-to-day function being more difficult with poor bone health. It is estimated that diet and exercise during childhood can impact peak bone mass as an adult nearly 20–40%. One study done on children with developmental coordination disorder found an increase in bone mass up to 4% and 5% in the cortical areas of the tibia alone from a 13-week training period. Peak bone mass occurs between the second and third decade of most people's lives. Studies have shown that increasing calcium stores in childhood via food intake result in significant improvements in bone-mass density and overall health, even into adulthood.
=== Filler injections === Filler injections of collagen can be used to raise atrophic scars to the level of surrounding skin. Risks vary based upon the filler used, and can include further disfigurement and allergic reaction.
The Medical Companion, Or Family Physician, a book from 1827, gave the following recipe: Paregoric Elixir – Take of purified opium, flowers of Benzoin, camphor, and essential oil of annis-seed, each, two drachms; brandy, two pints. Digest for eight or ten days, frequently shaking the bottle, and then strain the elixir.
=== Legal status === Bulevirtide was approved for medical use in the European Union in July 2020, in Canada in August 2025, and in the United States in May 2026. The US Food and Drug Administration granted the application for bulevirtide priority review, breakthrough therapy, and orphan drug designations.
Sources: en.wikipedia.org
=== Unicellular organisms === Serotonin is used by a variety of single-cell organisms for various purposes. SSRIs have been found to be toxic to algae. The gastrointestinal parasite Entamoeba histolytica secretes serotonin, causing a sustained secretory diarrhea in some people. Patients infected with E. histolytica have been found to have highly elevated serum serotonin levels, which returned to normal following resolution of the infection. E. histolytica also responds to the presence of serotonin by becoming more virulent. This means serotonin secretion not only serves to increase the spread of entamoebas by giving the host diarrhea but also serves to coordinate their behaviour according to their population density, a phenomenon known as quorum sensing. Outside the gut of a host, there is nothing that the entamoebas provoke to release serotonin, hence the serotonin concentration is very low. Low serotonin signals to the entamoebas they are outside a host and they become less virulent to conserve energy. When they enter a new host, they multiply in the gut, and become more virulent as the enterochromaffine cells get provoked by them and the serotonin concentration increases.
== Biomedical Science in Israel == In Israel, biomedical science is offered as an academic program at several major institutions, including the Hebrew University of Jerusalem, Tel Aviv University, the Technion – Israel Institute of Technology, and Ben-Gurion University of the Negev. These programs integrate coursework in molecular biology, genetics, biochemistry, physiology, and immunology with extensive laboratory training and research projects. Many faculty members involved in teaching are also active researchers or clinicians in affiliated hospitals and research centers, and students often participate in laboratory rotations, research internships, and collaborative projects with clinical departments. Graduates commonly proceed to advanced degrees (M.Sc. or Ph.D.) in biomedical and life sciences, join research laboratories in universities, hospitals, biotechnology firms, or pharmaceutical companies, or use the degree as preparation for professional studies such as medicine, dentistry, pharmacy, or public health. In addition, many graduates work in the pharmaceutical and drug-development industry, contributing to preclinical research, diagnostic development, and translational projects. The close ties between universities and major medical centers provide opportunities for exposure to translational and clinical research throughout their studies.
==== Catalytic (enzyme-substrate) peptide biosensors ==== Some peptide biosensors employ peptides that act as substrates for specific enzymes such as Proteases and kinases. When the enzyme cleaves, modifies or phosphorylates the peptide substrate, the resulting structural change produces a measurable signal. Signal markers, commonly fluorescence or electrochemical output, can also be conjugated to the peptide substrate for more efficient measurable signal.
The Young's modulus of a single protein can be found through molecular dynamics simulation. Using either atomistic force-fields, such as CHARMM or GROMOS, or coarse-grained forcefields like Martini, a single protein molecule can be stretched by a uniaxial force while the resulting extension is recorded in order to calculate the strain. Experimentally, methods such as atomic force microscopy can be used to obtain similar data. The internal dynamics of proteins involve subtle elastic and plastic deformations induced by viscoelastic forces, which can be probed by nano-rheology techniques. At the macroscopic level, the Young's modulus of cross-linked protein networks can be obtained through more traditional mechanical testing. Experimentally observed values for a few proteins can be seen below.
Sources: en.wikipedia.org
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.
Both are synthetic analogues derived from the same parent hormone. Reference descriptions usually characterise afamelanotide as more selective for the MC1R subtype, whereas melanotan-2 is reported to interact with a wider range of melanocortin receptors.
Early studies explored melanocortin signalling and pigmentation, which later led to informal use of the label tanning peptide. That label is not a regulatory category and does not imply approved status for any purpose.
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.