If you have been reading about amino acid substitution 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 2026-01-30. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic cyclic heptapeptide | Analog of alpha-MSH with an internal lactam bridge |
| Molecular weight | Approximately 1024 daltons | Free base value; salt forms differ |
| Appearance | White to off-white powder | Usually supplied as a lyophilized solid |
| Solubility | Freely soluble in water | Poorly soluble in nonpolar solvents |
| Typical storage | −20 °C, dry, protected from light | Repeated freeze-thaw cycles degrade peptides |
Human data remain limited and mostly short-term. Reports describe small trials and observational accounts rather than large controlled studies, so questions about dose-response relationships and long-term effects on melanocytes stay open. Whether repeated exposure alters naevus behaviour is not settled in the published record. Researchers also note that self-administered use outside clinical settings makes actual exposure difficult to quantify. Statements about efficacy and safety should therefore be read as preliminary rather than established.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
=== Dietary sources === Arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. Preterm infants are unable to synthesize arginine internally, making the amino acid nutritionally essential for them. Most healthy people do not need to supplement with arginine because it is a component of all protein-containing foods and can be synthesized in the body from glutamine via citrulline. Additional, dietary arginine is necessary for otherwise healthy individuals temporarily under physiological stress, for example during recovery from burns, injury or sepsis, or if either of the major sites of arginine biosynthesis, the small intestine and kidneys, have reduced function, because the small bowel does the first step of the synthesizing process and the kidneys do the second. Arginine is an essential amino acid for birds, as they do not have a urea cycle. For some carnivores, for example cats, dogs and ferrets, arginine is essential, because after a meal, their highly efficient protein catabolism produces large quantities of ammonia which need to be processed through the urea cycle, and if not enough arginine is present, the resulting ammonia toxicity can be lethal. This is not a problem in practice, because meat contains sufficient arginine to avoid this situation. Animal sources of arginine include meat, dairy products, and eggs, and plant sources include seeds of all types, for example grains, beans, and nuts.
== Mechanism == NADK phosphorylates NAD+ at the 2’ position of the ribose ring that carries the adenine moiety. It is highly selective for its substrates, NAD and ATP, and does not tolerate modifications either to the phosphoryl acceptor, NAD, or the pyridine moiety of the phosphoryl donor, ATP. NADK also uses metal ions to coordinate the ATP in the active site. In vitro studies with various divalent metal ions have shown that zinc and manganese are preferred over magnesium, while copper and nickel are not accepted by the enzyme at all. A proposed mechanism involves the 2' alcohol oxygen acting as a nucleophile to attack the gamma-phosphoryl of ATP, releasing ADP.
Ancient pyramidical structures, mausoleums, ruined cities and stone walls, such as the Wargaade Wall, are evidence of an old civilisation that once thrived in the Somali peninsula. This civilisation enjoyed a trading relationship with ancient Egypt and Mycenaean Greece since the second millennium BC, supporting the hypothesis that Somalia or adjacent regions were the location of the ancient Land of Punt. The Puntites native to the region traded myrrh, spices, gold, ebony, short-horned cattle, ivory and frankincense with the Egyptians, Phoenicians, Babylonians, Indians, Chinese and Romans through their commercial ports. An Egyptian expedition sent to Punt by the 18th dynasty Queen Hatshepsut is recorded on the temple reliefs at Deir el-Bahari, during the reign of the Puntite King Parahu and Queen Ati. In the classical era, the Macrobians, who may have been ancestral to Somalis, established a powerful kingdom that ruled large parts of modern Somalia. They were reputed for their longevity and wealth, and were said to be the "tallest and handsomest of all men". The Macrobians were warrior herders and seafarers. According to Herodotus' account, the Persian Emperor Cambyses II, upon his conquest of Egypt in 525 BC, sent ambassadors to Macrobia, bringing luxury gifts for the Macrobian king to entice his submission.
The coenzyme NAD+ was first discovered by the British biochemists Arthur Harden and William John Young in 1906. They noticed that adding boiled and filtered yeast extract greatly accelerated alcoholic fermentation in unboiled yeast extracts. They called the unidentified factor responsible for this effect a coferment. Through a long and difficult purification from yeast extracts, this heat-stable factor was identified as a nucleotide sugar phosphate by Hans von Euler-Chelpin. In 1936, the German scientist Otto Heinrich Warburg showed the function of the nucleotide coenzyme in hydride transfer and identified the nicotinamide portion as the site of redox reactions. Vitamin precursors of NAD+ were first identified in 1938, when Conrad Elvehjem showed that liver has an "anti-black tongue" activity in the form of nicotinamide. Then, in 1939, he provided the first strong evidence that nicotinic acid is used to synthesize NAD+. In the early 1940s, Arthur Kornberg was the first to detect an enzyme in the biosynthetic pathway. In 1949, the American biochemists Morris Friedkin and Albert L. Lehninger proved that NADH linked metabolic pathways such as the citric acid cycle with the synthesis of ATP in oxidative phosphorylation. In 1958, Jack Preiss and Philip Handler discovered the intermediates and enzymes involved in the biosynthesis of NAD+; salvage synthesis from nicotinic acid is termed the Preiss-Handler pathway. In 2004, Charles Brenner and co-workers uncovered the nicotinamide riboside kinase pathway to NAD+. The non-redox roles of NAD(P) were discovered later.
Sources: en.wikipedia.org
A supercentenarian, sometimes hyphenated as super-centenarian, is a person who has reached the age of 110 years. This age milestone is only achieved by about one in a thousand centenarians. Even rarer is a person who has lived to 115. There are 82 people in recorded history who have indisputably reached 115. Only three of the people who have reached 115 are men. Ethel Caterham, Naomi Whitehead, Lucia Laura Sangenito, Yolanda Beltrão de Azevedo, and Beatriz Ferreira Duarte are the only people currently alive who have verifiably reached the 115 year milestone. Jeanne Calment from France is the only age-verified person in human history to have reached the age of 120 years.
Pagoclone is an anxiolytic agent from the cyclopyrrolone family, related to better-known drugs such as the sleeping medication zopiclone. It was synthesized by a French team working for Rhone-Poulenc & Rorer S.A. Pagoclone belongs to the class of nonbenzodiazepines, which have similar effects to the older benzodiazepine group, but with quite different chemical structures. It was never commercialised. It binds with roughly equivalent high affinity (0.7–9.1 nM) to the benzodiazepine binding site of human GABAA receptors containing either an α1, α2, α3 or α5 subunit. It is a partial agonist at α1-, α2- and α5-containing GABAA receptors and a full agonist at receptors containing an α3 subunit. In rats 5′-hydroxypagoclone was identified as a major metabolite. This metabolite has a considerably greater efficacy at the α1 subtype than the parent compound and was shown to have significant anxiolytic-like activity and to produce sedation. In contrast to zopiclone, pagoclone produces anxiolytic effects with little sedative or amnestic actions at low doses (0.3mg to 1.2mg per day). The pharmacologist David Nutt has suggested pagoclone as a possible base from which to make a better social drug, as it produces the positive effects of alcohol, such as relaxation and sociability, but without also causing the negative effects like aggression, amnesia, nausea, loss of coordination and liver damage. Its effect can be quickly reversed by the action of flumazenil, which is already used as an antidote to benzodiazepine overdose.
Moreover, engineered knottins have shown significant promise as therapeutics, imaging agents, and targeting agents for chemotherapy. The mammalian proteins Agouti signalling peptide and Agouti related peptide are the only known mammalian examples of this motif. Both are neuropeptides involved in cell signalling. The former is responsible for hair (fur) colouration. The motif is similar to the cyclic cystine knot or cyclotide, but lacks the cyclisation of the polypeptide backbone which is present in the latter family. The growth factor cystine knot (GFCK) is similar to the ICK but its topology is such that it is the bond between the first and fourth disulfide which threads through the loop.
There remained areas with noticeable German minorities in the westernmost borderland around Cheb, where skilled ethnic German miners and workers continued in mining and industry, until 1955, as sanctioned under the Yalta Conference protocols; in the Egerland, German minority organizations continue to exist. In the 2021 census, 24,632 people in the Czech Republic claimed German ethnicity, 15,504 of which in combination with another ethnicity, a sharp reduce compared to the 3,123,568 Germans reportedly living in the Czechoslovak Republic in 1921. In the modern day, the Bohemian German dialects and the Moravian German dialects have largely disappeared because remaining Germans employ Standard German.
He played for Queens Park Rangers and Manchester United. Gemma Ray, musician, singer, composer and producer, raised in Billericay Charlie Richardson, gangster, lived in Billericay Stewart Robson, footballer, born in Billericay Joseph Thornton, 19th-century Oxford-based bookseller, born in Billericay Russell Tovey, actor, has Billericay as his home town Paul Walter, cricketer, born in Billericay Patrick W. Welch, painter, born in Billericay Charlie Wernham, comedian and comedy actor, born and lives in Billericay Ben Wheatley, film director, born in Billericay.
Sources: en.wikipedia.org
=== From ore === α-spodumene is roasted at 1100 °C for 1h to make β-spodumene, then roasted at 250 °C for 10 minutes with sulfuric acid. As of 2020, Australia was the world's largest producer of lithium intermediates, all based on spodumene. In recent years mining companies have begun exploration of lithium projects throughout North America, South America and Australia to identify economic deposits that can potentially bring new supplies of lithium carbonate online to meet the growing demand for the product.
High expression of CLIP favors the release of IL-4 and Th2 cell polarization. CLIP plays an important role in preventing autoimmunity. Since MHC is a polymorphic molecule, mutations that prevent CLIP from binding to MHC II leave the peptide binding groove empty. This could lead to the binding of other self-peptides and destruction of healthy cells. Autoimmune diseases such as rheumatoid arthritis, juvenile dermatomyositis, and Graves disease are all associated with low CLIP protein levels.
In Portugal, public prosecution is conducted by the Public Prosecution Service which is headed by the prosecutor general. The main police organisations of Portugal are the Guarda Nacional Republicana (National Republican Guard), the Polícia de Segurança Pública (Public Security Police), a civilian police force that works in urban areas; and the Polícia Judiciária (Judiciary Police), a senior criminal police body, under the authority of the Minister of Justice and endowed with administrative autonomy. Portugal has 49 correctional facilities run by the Directorate-General for Reintegration and Prison Services (DGRSP). The facilities are classified by security level, and by degree of management complexity, and often house inmates with different legal statuses, risk levels, and criminal trajectories within the same facilities. Despite following a reintegration-oriented penal model, Portugal retains high prison occupancy and an average sentence length of 31.3 months and one of the world's highest prison suicide rates representing around 30% of the 60 to 70 deaths occurring annually.
=== Structure === Honokiol belongs to a class of neolignan biphenols. As a polyphenol it is relatively small and can interact with cell membrane proteins through intermolecular interactions like hydrogen bonding, hydrophobic interactions, or aromatic pi orbital co-valency. It is hydrophobic and readily dissolved in lipids. It is structurally similar to propofol.
=== Pharmacodynamics === ETH-LAD acts as a serotonin receptor agonist, including of the serotonin 5-HT2A receptor. It shows greater potency and efficacy as a serotonin 5-HT2A receptor agonist than LSD in vitro. In addition to the serotonin 5-HT2A receptor, the drug binds with high affinity to the serotonin 5-HT1A and 5-HT2C receptors. Like LSD, ETH-LAD also binds with lower affinity to the dopamine D1, D2, D3, D4, and D5 receptors. ETH-LAD shows psychedelic-like effects in animals, specifically rodent drug discrimination tests. It is about 1.6- to 2.3-fold more potent than LSD in these tests. Similarly to LSD, ETH-LAD shows moderate anti-inflammatory effects in preclinical research, but with slightly higher potency.
Sources: en.wikipedia.org
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.
Melanotan-1, also called afamelanotide, is a shorter linear analog with a different amino acid sequence and no lactam ring. It has been evaluated in formal clinical programs, while melanotan-2 has not. The two are distinct molecules and are not interchangeable.
No. Bremelanotide is a related but distinct cyclic peptide that reached approved status for one specific clinical indication. Melanotan-2 is a separate molecule with its own sequence and properties. Shared ancestry in the melanocortin family does not make them the same substance.
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.