A practical reference on amino acid substitution: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-11-20. Anything still debated is marked as such rather than presented as settled.
Melanotan II is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, a naturally occurring peptide involved in pigmentation signalling. Its structure substitutes a lactam bridge between side chains to increase stability relative to the native hormone. The compound is also known by the shorthand MT-II and by several non-proprietary synonyms used in research catalogues. It is not an approved therapeutic product in any major jurisdiction; material sold under this name is typically offered as a laboratory reagent rather than as a medicine.
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.
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.
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Analogue of alpha-melanocyte-stimulating hormone |
| Common synonyms | MT-II; melanotan 2 | No internationally accepted non-proprietary name |
| Typical presentation | Lyophilised powder in a sealed vial | Often supplied alongside a separate diluent |
| Regulatory status | Unapproved therapeutic substance | Customs seizure reported in several jurisdictions |
| Reported route in use | Subcutaneous injection | Self-administered outside clinical settings |
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.
Receptor studies place melanotan-2 among non-selective melanocortin agonists, binding MC1R, MC3R, MC4R and MC5R rather than a single subtype. Activation of MC1R on cutaneous melanocytes raises tyrosinase activity and shifts pigment synthesis toward eumelanin, which is darker and more photostable than pheomelanin. Central receptors, particularly MC4R, are associated with appetite suppression and with reported effects on sexual function. Because subtype selectivity is low, the same molecule engages pigment, metabolic and vascular pathways at once, and this breadth is a common explanation offered for the range of adverse events described in user reports.
No regulatory authority has approved melanotan-2 for human use, and several countries classify it as a prescription-only or controlled substance, which restricts lawful supply. Material sold online is generally labelled as a research chemical and is not required to meet pharmaceutical standards of identity or purity. Published human data consist mainly of small uncontrolled studies, case reports and adverse-event notifications, so the evidence base is descriptive rather than confirmatory. Whether repeated melanocyte stimulation alters long-term naevus behaviour remains an open question that no completed trial has resolved.
Published human data come mostly from small, short studies rather than large controlled trials. Reported outcomes include increased skin pigmentation and, in some reports, effects on appetite and libido, but sample sizes are small and follow-up is limited. Whether long-term use produces durable pigment changes or adverse effects is not established. Because products sold outside pharmacies are not standardized, the actual content of any given vial is often unknown. Independent testing of such material is uncommon.
Melanotan II is a synthetic cyclic heptapeptide analog derived from the core sequence of alpha-melanocyte-stimulating hormone. Researchers at the University of Arizona synthesized it during the 1980s while studying pigmentation and appetite signaling. The compound is not an approved medicine in any major jurisdiction and appears mainly in laboratory and research-chemical settings. Its structure incorporates a lactam bridge between side chains, which constrains the ring and slows enzymatic breakdown relative to the natural hormone.
Melanotan II binds several melanocortin receptor subtypes rather than a single target. MC1R on melanocytes drives melanin synthesis, while MC3R and MC4R participate in energy balance, appetite, and sexual response pathways. This lack of selectivity explains why reported effects extend beyond skin darkening. Substitutions at positions four and seven, including norleucine and D-phenylalanine, increase potency and resistance to peptidases. Understanding which receptor mediates which effect remains an active area of investigation.
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.
== March 2016 reconstitution == In December 2015, Kim Hames announced his intention to resign as deputy leader of the Liberal Party (and thus also as deputy premier) with effect from February 2016. Liza Harvey was elected unopposed as his successor, with a resultant ministerial reshuffle that took effect from 31 March 2016. Another reshuffle took place on 22 September 2016, with the resignations of Dean Nalder and Tony Simpson. All ministers are listed in order of seniority.
=== Nomenclature === Standardized GST nomenclature first proposed in 1992 identifies the species to which the isozyme of interest belongs with a lower-case initial (e.g., "h" for human), which precedes the abbreviation GST. The isozyme class is subsequently identified with an upper-case letter (e.g., "A" for alpha), followed by an Arabic numeral representing the class subfamily (or subunit). Because both mitochondrial and cytosolic GSTs exist as dimers, and only heterodimers form between members of the same class, the second subfamily component of the enzyme dimer is denoted with a hyphen, followed by an additional Arabic numeral. Therefore, if a human glutathione S-transferase is a homodimer in the pi-class subfamily 1, its name will be written as "hGSTP1-1." The early nomenclature for GSTs referred to them as Y proteins, referring to their separation in the Y fraction (as opposed to the "X and Z" fractions) using Sephadex G75 chromatography. As GST sub-units were identified they were referred to as Ya, Yp, etc. with if necessary, a number identifying the monomer isoform (e.g. Yb1). Litwack et al proposed the term Ligandin to cover the proteins previously known as Y proteins. In clinical chemistry and toxicology, the terms alpha GST, mu GST, and pi GST are most commonly used.
=== Other reactions === A radical SAM enzyme with intrinsic lyase activity is able to catalyze lysine transfer reaction, generating archaea-specific archaosine-containing tRNAs. Viperin is an interferon-stimulated radical SAM enzyme which converts CTP to ddhCTP (3ʹ-deoxy-3′,4ʹdidehydro-CTP), which is a chain terminator for viral RdRps and therefore a natural antiviral compound.
Sources: en.wikipedia.org
Real advancement came in the early 1800s, when Linnaeus's student Erik Acharius—later hailed as the "father of lichenology"—re-examined the group. From 1798 to 1814, Acharius published four influential monographs that divided Lichen into numerous genera and sketched a finer hierarchy: Lichenographiae Suecicae Prodromus (1798), Methodus (1803), Lichenographia Universalis (1810), and Synopsis Methodica Lichenum (1814). Beyond cataloguing hundreds of species, he introduced microscopic characters—such as the structure of the spore-producing bodies (apothecia)—as classificatory tools. His anatomical focus freed lichenology from its old dependence on thallus form (crustose, foliose, fruticose) and laid the groundwork for a multi-character "natural" system. During the early–mid 1800s, lichen taxonomists steadily wove fresh microscopic insights into their work. With compound microscopes common by the 1830s, researchers saw that lichens contain distinct internal layers and reproductive organs. A cadre of European "microscope taxonomists"—Antoine Fée, Giuseppe De Notaris, Vittore Trevisan, Camille Montagne, Ernst Stizenberger and Edward Tuckerman—used those details to delimit genera on ascospore shape, septation and exciple anatomy, giving lichenology its first genuinely anatomical classification. Meanwhile, William Nylander drew on micro‑anatomy to craft a far richer hierarchical scheme, describing hundreds of new taxa yet largely ignoring spore data.
Alfred Nobel was born on 21 October 1833 in Stockholm, Sweden, into a family of engineers. He was a chemist, engineer and inventor who amassed a fortune during his lifetime, most of it from his 355 inventions, of which dynamite is the most famous. He was interested in experimental physiology and set up his own labs in France and Italy to conduct experiments in blood transfusions. Keeping abreast of scientific findings, he was generous in his donations to Ivan Pavlov's laboratory in Russia and was optimistic about the progress resulting from scientific discoveries made in laboratories. In 1888, Nobel was surprised to read his own obituary, titled "The Merchant of death Is Dead", in a French newspaper. As it happened, it was Nobel's brother Ludvig who had died, but Nobel, unhappy with the content of the obituary and concerned that his legacy would reflect poorly on him, was inspired to change his will. In his last will, Nobel requested that his money be used to create a series of prizes for those who confer the "greatest benefit on mankind" in physics, chemistry, peace, physiology or medicine, and literature. Though Nobel wrote several wills during his lifetime, the last was written a little over a year before he died in 1896 at the age of 63. Because his will was contested, it was not approved by the Storting (Norwegian Parliament) until 26 April 1897. After Nobel's death, the Nobel Foundation was set up to manage the assets of the bequest. In 1900, the Nobel Foundation's newly created statutes were promulgated by Swedish King Oscar II.
The Affordable Insulin Now Act is a bill in the United States Congress intended to cap out-of-pocket insulin prices under private health insurance and Medicare at no more than $35 per month. The bill was first introduced on February 25, 2022, by Representative Angie Craig (D-MN). On March 31, 2022, the bill passed the House of Representatives, 232–193. A version of the bill contained in the Inflation Reduction Act (IRA) for private health insurance was blocked by Senate Republicans on August 8, 2022. However, the inflation reduction legislation did cap out-of-pocket insulin cost at $35 per monthly prescription for the following: Medicare Part D enrollees, which was legislated at effective on January 1, 2023. Medicare Part B enrollees, which was effective starting on July 1, 2023.
Sources: en.wikipedia.org
Botulinum neurotoxins (BoNTs) are the causative agents of the deadly food poisoning disease botulism, and could pose a major biological warfare threat due to their extreme toxicity and ease of production. They also serve as powerful tools to treat an ever expanding list of medical conditions that benefit from its paralytic properties, an example drug with BoNTs as the active ingredient is Botox. TBotulinum neurotoxins (BoNTs) are protein neurotoxins that are produced by the bacteria Clostridium. BoNTs are now largely being studied due to their ability to aid in chronic inflammatory diseases such as acne, multiple sclerosis, and for cosmetic purposes.
Smoking of opium came on the heels of tobacco smoking and may have been encouraged by a brief ban on the smoking of tobacco by the Ming emperor. The prohibition ended in 1644 with the coming of the Qing dynasty, which encouraged smokers to mix in increasing amounts of opium. In 1705, Wang Shizhen wrote: "nowadays, from nobility and gentlemen down to slaves and women, all are addicted to tobacco". Tobacco in that time was frequently mixed with other herbs (this continues with clove cigarettes to the modern day), and opium was one component in the mixture. Tobacco mixed with opium was called madak (or madat) and became popular throughout China and its seafaring trade partners (such as Taiwan, Java, and the Philippines) in the 17th century. In 1712, Engelbert Kaempfer described addiction to madak: "No commodity throughout the Indies is retailed with greater profit by the Batavians than opium, which [its] users cannot do without, nor can they come by it except it be brought by the ships of the Batavians from Bengal and Coromandel." Fueled in part by the 1729 ban on madak, which at first effectively exempted pure opium as a potentially medicinal product, the smoking of pure opium became more popular in the 18th century. In 1736, the smoking of pure opium was described by Huang Shujing, involving a pipe made from bamboo rimmed with silver, stuffed with palm slices and hair, fed by a clay bowl in which a globule of molten opium was held over the flame of an oil lamp.
Chemically it is a hydantoin derivative, but does not exhibit antiepileptic activity like other hydantoin derivates such as phenytoin. The poor water solubility of dantrolene leads to certain difficulties in its use. A more water-soluble analog of dantrolene, azumolene, is under development for similar indications. Azumolene has a bromine residue instead of the nitro group found in dantrolene, and is 30 times more water-soluble.
=== 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.
Sources: en.wikipedia.org
No. No major regulatory agency has granted a marketing authorisation for melanotan II as a medicine. Products sold under this name are generally presented as laboratory reagents and are not subject to the batch-release testing applied to approved drugs.
It was developed in the 1980s by researchers investigating analogues of alpha-melanocyte-stimulating hormone for pigmentation and related endpoints. Early work included small human studies during the 1990s. Development did not progress to licensing, and the compound remained a research and grey-market item.
Peptides are prone to truncation, oxidation and aggregation during synthesis and handling. Without independent testing, a buyer cannot confirm the identity or the content of a vial. Analytical surveys of unapproved peptide products have repeatedly found discrepancies between label claims and measured composition.
No. It is a synthetic analogue carrying four amino acid changes, a lactam ring and an amidated C-terminus. The natural hormone is a linear thirteen-amino-acid peptide processed from proopiomelanocortin.