melanocortin receptors raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-06-20. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Analog of alpha-melanocyte-stimulating hormone |
| Primary receptor family | Melanocortin receptors MC1R through MC5R | Binding is not subtype-selective |
| Development period | 1980s | Synthesized during pigmentation and appetite research |
| Regulatory status | Not an approved medicine | No major regulator has authorized human use |
| Related compound | Afamelanotide | Linear analog studied for photoprotection |
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.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone, the naturally occurring peptide involved in pigmentation signalling. Its sequence is conventionally written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, with a lactam bridge joining the aspartate side chain to the lysine side chain. The empirical formula is C50H69N15O9 and the monoisotopic mass lies near 1023.5 daltons. N-terminal acetylation and the D-configured phenylalanine both increase resistance to enzymatic breakdown compared with the parent hormone.
Pharmacologically, melanotan-2 behaves as a non-selective agonist across the melanocortin receptor family. Binding at MC1R on dermal melanocytes promotes eumelanin synthesis, which underlies the tanning response described in early human work. Activity at the centrally expressed MC4R receptor is associated with reported effects on appetite and erectile function. Because the peptide does not discriminate strongly among receptor subtypes, attributing any single observed effect to one receptor pathway is generally not possible without selective antagonists or receptor knockout models.
=== Biological === An MRI study conducted on Price provides a plausible argument as to the neurological foundation of her superior memory. Both the temporal lobe and the caudate nucleus were found to be enlarged. Parker and colleagues speculated that a defective frontostriatal circuit could be responsible for the observed executive function deficits in hyperthymesia. This circuit plays a crucial role in some neurodevelopmental disorders including obsessive–compulsive disorder and Alzheimer's. Given the parallels in some aspects of behavior, Price's hyperthymestic abilities possibly stem from atypical neurodevelopment. Scientists now need to ascertain if and how these brain areas are connected to establish a coherent neurological model for superior autobiographical memory. For autobiographical memory, the hippocampus, located in the medial temporal lobe, is involved in the encoding of declarative memory (memory for facts and events), while the temporal cortex is involved in the storage of such memory. The caudate nucleus is primarily associated with procedural memory, in particular habit formation, and is, therefore, intrinsically linked to obsessive-compulsive disorder. A 2018 clinical trial published that there were higher levels of activation in the medial prefrontal cortex and temporoparietal junction along with heightened connection between the prefrontal cortex and the hippocampus in hyperthymesiacs, suggesting that these regions may play a role in the enablement of the condition.
==== 1000–1099 ==== Export of Goods (Control) (Amendment) Order 1993 (S.I. 1993/1020) Foreign Satellite Service Proscription Order 1993 (S.I. 1993/1024) Social Security (Consequential Provisions) Act 1992 Appointed Day Order 1993 (S.I. 1993/1025) Cranfield Airport (Designation) (Detention and Sale of Aircraft) Order 1993 (S.I. 1993/1026) Weymouth and Portland Harbour Revision Order 1993 (S.I. 1993/1027) Town and Country Planning (General Permitted Development) (Scotland) Amendment Order 1993 (S.I. 1993/1036) Gaming Act (Variation of Monetary Limits) (Scotland) Order 1993 (S.I. 1993/1037) Town and Country Planning (Use Classes) (Scotland) Amendment Order 1993 (S.I. 1993/1038) Town and Country Planning (General S.I. 1993/1039) Gaming Clubs (Hours and Charges) (Scotland) Amendment Regulations 1993 (S.I. 1993/1040) Reconstitution of the Bedfordshire and River Ivel Internal Drainage Board Order 1993 (S.I. 1993/1041) Glan Conwy-Conwy Morfa Trunk Road (A547) (Previously known as and forming part of The Chester—Bangor Trunk Road (A55)) Detrunking Order 1993 (S.I. 1993/1057) International Finance Corporation (1991 General Capital Increase) Order 1993 (S.I. 1993/1059) Asian Development Bank (Fifth Replenishment of the Asian Development Fund and Second Regularized Replenishment of the Technical Assistance Special Fund) Order 1993 (S.I. 1993/1060) Banking Appeal Tribunal (Scottish Appeals) Amendment Regulations 1993 (S.I. 1993/1061) Financial Assistance for Environmental Purposes Order 1993 (S.I. 1993/1062) A43 Trunk Road (Silverstone Bypass and Slip Roads) Order 1993 (S.I.
==== Identification of the formula ==== In the early 1700s, Georg Ernst Stahl claimed that reacting sulfuric acid with limestone produced a sort of alum. The error was soon corrected by Johann Pott and Andreas Marggraf, who showed that the precipitate obtained when an alkali is poured into a solution of alum, namely alumina, is quite different from lime and chalk, and is one of the ingredients in common clay. Marggraf also showed that perfect crystals with properties of alum can be obtained by dissolving alumina in sulfuric acid and adding potash or ammonia to the concentrated solution. In 1767, Torbern Bergman observed the need for potassium or ammonium sulfates to convert aluminium sulfate into alum, while sodium or calcium would not work. At the time, potassium ("potash") was believed to be exclusively found on plants. However, in 1797, Martin Klaproth discovered the presence of potassium in the minerals leucite and lepidolite. Louis Vauquelin then conjectured that potassium was likewise an ingredient in many other minerals. Given Marggraf and Bergman's experiments, he suspected that this alkali constituted an essential ingredient of natural alum. In 1797 he published a dissertation demonstrating that alum is a double salt, composed of sulfuric acid, alumina, and potash. In the same journal volume, Jean-Antoine Chaptal published the analysis of four different kinds of alum, namely, Roman alum, Levant alum, British alum and alum manufactured by himself, confirming Vauquelin's results.
Klüver wrote that "many 'atypical' visions are upon close inspection nothing but variations of these form-constants." An unusual but unique characteristic of mescaline use is the "geometrization" of three-dimensional objects. The object can appear flattened and distorted, similar to the presentation of a Cubist painting. Detailed descriptions of the psychedelic experience induced by mescaline have been given by many authors. The subjective effects of mescaline are qualitatively similar to those of LSD and psilocybin. Based on anecdotal evidence however, mescaline is said to be less threatening and to produce less ego dissolution than other psychedelics like LSD. This may in part be due its slow onset allowing for a more comfortable ease-in of effects. In addition, mescaline is typically dosed at lower doses than LSD or psilocybin in terms of doses with equivalent or comparable strength. According to a study in the Netherlands, ceremonial San Pedro use seems to be characterized by relatively strong spiritual experiences, and low incidence of challenging experiences. Mescaline, LSD, and psilocybin appear to produce similar color enhancement in clinical studies, though more research is needed.
=== New Zealand === PCP was used in New Zealand as a timber preservative and antisapstain treatment, but since 1988 is no longer used. It was also sold as a moss killer to the general public (by Shell, at least) in the form of a 115g/L aqueous solution and labelled as a poison.
Sources: en.wikipedia.org
Lysine (symbol Lys or K; also L-lysine) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated −NH+3 form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group (which is in the deprotonated −COO− form when the lysine is dissolved in water at physiological pH), and a side chain (CH2)4NH2 (which is partially protonated when the lysine is dissolved in water at physiological pH), and so it is classified as a basic, charged (in water at physiological pH), aliphatic amino acid. It is encoded by the codons AAA and AAG. Like almost all other amino acids, the α-carbon is chiral and lysine may refer to either enantiomer or a racemic mixture of both. For the purpose of this article, lysine will refer to the biologically active enantiomer L-lysine, where the α-carbon is in the S configuration. The human body cannot synthesize lysine. It is essential in humans and must therefore be obtained from the diet. In organisms that synthesize lysine, two main biosynthetic pathways exist, the diaminopimelate and α-aminoadipate pathways, which employ distinct enzymes and substrates and are found in diverse organisms. Lysine catabolism occurs through one of several pathways, the most common of which is the saccharopine pathway. Lysine plays several roles in humans, most importantly proteinogenesis, but also in the crosslinking of collagen polypeptides, uptake of essential mineral nutrients, and in the production of carnitine, which is key in fatty acid metabolism.
=== Orientational anisotropy === SHG polarization anisotropy can be used to determine the orientation and degree of organization of proteins in tissues since SHG signals have well-defined polarizations. By using the anisotropy equation:
Maresch (1905) introduced Bielschowsky's silver impregnation technic for neurofibrils as a stain for reticulum fibers, but emphasized the nonspecificity of such procedures. This lack of specificity has been some confirmed repeatedly. Yet, since the 1920s the definition of "reticulin" and studies of its distribution were based solely on silver impregnation technics. The chemical mechanism and specificity of this group of stains is obscure. Application of Gömöri's and Wilder's methods to human tissues showed variations of staining patterns with the fixatives and technics employed. Besides reticulum fibers, various other tissue structures, e.g. I bands of striated muscle, fibers in nervous tissues, and model substances, e.g. polysaccharides, egg white, gliadin, were also stained. Deposition of silver compounds on reticulum fibers was limited to an easily removable substance; the remaining collagen component did not bind silver. These histochemical studies indicate that silver impregnation technics for reticulum fibers have no chemical significance and cannot be considered as histochemical technics for "reticulin" or type III collagen.
Caesium-135's predecessor xenon-135 is produced at a high rate of over 6% of fissions, but is an extremely potent absorber of thermal neutrons (neutron poison), so that most of it is transmuted to almost-stable xenon-136 before it can decay to caesium-135. If 90% of 135Xe is destroyed, then the remaining 135Cs's decay energy per unit time is initially only about 1% as great as that of the 99Tc. In a fast reactor, less of the Xe-135 may be destroyed.135Cs is the only alkaline or electropositive LLFP; in contrast, the main medium-lived fission products and the minor actinides other than neptunium are all alkaline and tend to stay together during reprocessing; with many reprocessing techniques such as salt solution or salt volatilization, 135Cs will also stay with this group, although some techniques such as high-temperature volatilization can separate it. Often the alkaline wastes are vitrified to form high level waste, which will include the 135Cs.Fission caesium contains not only 135Cs but also stable but neutron-absorbing 133Cs (which wastes neutrons and forms 134Cs which is radioactive with a half-life of 2 years) as well as the common fission product 137Cs which does not absorb neutrons but is highly radioactive, making handling more hazardous and complicated; for all these reasons, transmutation disposal of 135Cs would be more difficult. Palladium-107 has a very long half-life, a low yield (though the yield for plutonium fission is higher than the yield from uranium-235 fission), and very weak radiation.
Sources: en.wikipedia.org
At the beginning of July 2024, Santiago Peña expressed his opposition to the flexibilization of Mercosur, arguing that it is more advantageous to negotiate as a bloc, and questioned Uruguay's position of moving forward with bilateral agreements. Although in the first days of his term he had shown a willingness toward extra-bloc agreements, at that time he adopted the opposite stance. Prior to the transfer of the rotating presidency of Mercosur to Uruguay, Peña pointed to the need to continue efforts to strengthen regional integration, acknowledging that the bloc is going through a period of challenges. In October 2024, Peña lowered expectations regarding an imminent trade agreement between Mercosur and the European Union, underscoring that, although the bloc has shown interest in moving toward a free trade agreement, it has not found an equivalent willingness in Europe. He described as "unacceptable" the lack of recognition by Brussels of Paraguay's sanitary certification institutions. In December of that same year, he aligned himself with the position of the president of Brazil, Luiz Inácio Lula da Silva, reaffirming that Paraguay will not support unilateral negotiations that could fragment Mercosur's cohesion.
Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish, reddish, or even greenish). In the reservoir it is usually found in association with natural gas (which being lighter forms a "gas cap" over the petroleum) and saline water (which being heavier than most forms of crude oil, generally sinks beneath it). Crude oil may also be found in a semi-solid form mixed with sand and water, as in the Athabasca oil sands in Canada, where it is usually referred to as crude bitumen. In Canada, bitumen is considered a sticky, black, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow. Venezuela also has large amounts of oil in the Orinoco oil sands, although the hydrocarbons trapped in them are less viscous than in Canada and are usually called extra heavy oil. Oil sands resources are called unconventional oil to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570×10^9 m3) of bitumen and extra heavy oil, about twice the volume of the world's reserves of conventional oil.
== Applications == FTIR can be used in all applications where a dispersive spectrometer was used in the past (see external links). In addition, the improved sensitivity and speed have opened up new areas of application. Spectra can be measured in situations where very little energy reaches the detector. Fourier transform infrared spectroscopy is used in geology, chemistry, materials, botany and biology research fields.
Sources: en.wikipedia.org
No regulator in a major market has approved it for human use. It appears in research settings and in products marketed outside pharmacy channels. Legal status for personal possession varies by country.
Afamelanotide is a linear analog that has received approval in some jurisdictions for a specific photoprotection indication. Melanotan II is cyclic and less selective across melanocortin receptors. The two are related but are not interchangeable in regulatory or clinical terms.
A compound that activates several receptor subtypes may produce effects beyond pigmentation. Selectivity influences which tissues respond and shapes the side-effect profile described in reports. Designing subtype-selective analogs is a stated goal of melanocortin research.
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.