A practical reference on eumelanin: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-02-10. Anything still debated is marked as such rather than presented as settled.
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.
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.
Melanotan-2 is a synthetic cyclic heptapeptide designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous tridecapeptide that regulates pigment production. Two modifications distinguish it from the natural hormone: norleucine replaces methionine at the N-terminus, which limits oxidation, and a D-phenylalanine substitution raises receptor affinity. The ring is closed through an aspartate-lysine lactam bridge, giving the molecule a constrained conformation. The free base has a molecular mass near 1024 daltons, and commercial material is usually supplied as an acetate salt. It appears in the literature as a research peptide rather than an approved therapeutic agent.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Cyclic heptapeptide, C-terminally amidated |
| Approximate molecular mass | 1024 Da | Monoisotopic mass of the free peptide |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility class | Soluble in water and polar solvents | Also dissolves in neutral aqueous buffer |
| Common synonyms | Melanotan II, MT-II, MT-2 | Described as a melanocortin agonist in early literature |
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
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.
Research interest has centred on photoprotection and pigmentation, with a smaller body of work on appetite and sexual function. Published human data remain limited to small, frequently uncontrolled studies, and the compound has never received marketing approval from a national medicines regulator. Most laboratory work treats it as a pharmacological tool for probing melanocortin signalling in cell culture or animal models. Whether pigmentation changes observed in people translate into measurable protection against ultraviolet-induced DNA damage remains an open question.
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.
Senate on 17 May 2005, Galloway said that he had "met Saddam Hussein exactly the same number of times as Donald Rumsfeld met him," but "The difference is Donald Rumsfeld met him to sell him guns ... I met him to try to bring about an end to sanctions, suffering and war". In the late 1990s, Galloway allegedly lost favour with Saddam Hussein after telling an interviewer that he supported the Iraqi people rather than their president. In 1999, he met with Uday Hussein, Saddam's son. On 6 May 2002, Galloway met with Deputy Prime Minister Tariq Aziz in Baghdad on his second visit to Iraq that year, accompanied by the Labour peer Nicolas Rea and Labour MPs Kerry Pollard and Robert Wareing. He was also scheduled to address a conference of solidarity with the Iraqi people. His party ran into the far-right Governor of Carinthia Jörg Haider returning from a meeting with Foreign Minister Naji Sabri. Galloway did not take his companions' suggestion to copy a scene from Casablanca by singing La Marsellaise in front of Haider. On 8 August 2002, two days after the Iraqi invitation to resume talks in Baghdad was rejected by the United Nations Security Council and against the mounting threat of US invasion, Galloway was received for the second time by Saddam Hussein. Per Galloway's account, the meeting took place in a secret underground bunker near Baghdad.
=== Polymorphism === Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism. It is a characteristic feature of cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa. In Hydrozoans, colonial individuals arising from individual zooids will take on separate tasks. For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free-living or sexually reproducing individuals, the medusae.
The players have access to a limited selection of Half-Life's weaponry to assist them in the game. The game is unique in the context of the Half-Life series in that it is the only game divided into separate missions, each with a specific objective to pursue, instead of consisting of a single unbroken narrative. How players perform in each mission is ranked at the conclusion of the level as a grade from "A" to "F". This score is based on each player's accuracy with weapons, the number of kills they acquired and the amount of damage they sustained during the course of the mission. Should players successfully complete the game's nine missions with "A" grades on every level, they are given access to a bonus cooperative mission, in which they can play as a pair of Vortigaunts, as well as the ability to play through the PlayStation 2 version of the original Half-Life as a Vortigaunt.
== Puberty onset == Puberty is preceded by adrenarche, marking an increase of adrenal androgen production between ages 6–10. Adrenarche is sometimes accompanied by the early appearance of axillary and pubic hair. The first androgenic hair resulting from adrenarche can be also transient and disappear before the onset of true puberty. The onset of puberty is associated with high GnRH pulsing, which precedes the rise in sex hormones, LH and FSH. Exogenous GnRH pulses cause the onset of puberty. Brain tumors which increase GnRH output may also lead to premature puberty. The cause of the GnRH rise is unknown. Leptin might be the cause of the GnRH rise. Leptin has receptors in the hypothalamus which synthesizes GnRH. Individuals who are deficient in leptin fail to initiate puberty. The levels of leptin increase with the onset of puberty, and then decline to adult levels when puberty is completed. The rise in GnRH might also be caused by genetics. A study discovered that a mutation in genes encoding both neurokinin B as well as the neurokinin B receptor can alter the timing of puberty. The researchers hypothesized that neurokinin B might play a role in regulating the secretion of kisspeptin, a compound responsible for triggering direct release of GnRH as well as indirect release of LH and FSH.
In 1913, chemists Frederick Soddy and Kasimir Fajans independently observed that alpha decay caused atoms to move down two places on the periodic table, while the loss of two beta particles restored it to its original position. Under the resulting reorganisation of the periodic table, radium was placed in group II, actinium in group III, thorium in group IV and uranium in group VI. This left a gap between thorium and uranium. Soddy predicted that this unknown element, which he referred to (after Dmitri Mendeleev) as "ekatantalium", would be an alpha emitter with chemical properties similar to tantalum. It was not long before Fajans and Oswald Helmuth Göhring discovered it as a decay product of a beta-emitting product of thorium. Based on the radioactive displacement law of Fajans and Soddy, this was an isotope of the missing element, which they named "brevium" after its short half-life. However, it was a beta emitter, and therefore could not be the mother isotope of actinium. This had to be another isotope of the same element. Hahn and Meitner set out to find the missing mother isotope. They developed a new technique for separating the tantalum group from pitchblende, which they hoped would speed the isolation of the new isotope. The work was interrupted by the First World War. Meitner became an X-ray nurse, working in Austrian Army hospitals, but she returned to the Kaiser Wilhelm Institute in October 1916.
Sources: en.wikipedia.org
== Biography == Born in Mwan in 1902, Mailo was educated at the Protestant Mission School at Anopouou. After leaving school in 1914, he worked on a trading boat between 1915 and 1920. The Japanese authorities appointed Mailo to the post of secretary of Moen island in 1932. The following year, he succeeded his uncle as Chief of Nepukos village. In 1936 he became Leader of Section No. 2 of Moen island, holding the role until 1938. Between 1939 and 1944 he was employed by the Japanese government as an advisor on native affairs. In 1947 he became Chief of Moen, succeeding his brother Albert. In 1957 the position was reconstituted as a mayoral post and made elective, with Mailo elected to the post. In the same year, he was elected to Truk Congress, serving as president of the legislature in 1957 and 1958. He also became president of the Truk Trading Company. In 1965 Mailo was elected to the General Assembly of the new Congress of the Trust Territory of the Pacific Islands as the Moen representative. The body was later renamed the House of Representatives and Mailo was re-elected in 1966, remaining in office until the 1968 elections. He subsequently served on the board of Air Micronesia. He died in Truk Hospital in September 1971 at the age of 68, survived by wife Chimako and eleven children.
The δ-opioid receptor, also known as delta opioid receptor or simply delta receptor, abbreviated DOR or DOP, is an inhibitory 7-transmembrane G-protein coupled receptor coupled to the G protein Gi/G0 and has enkephalins as its endogenous ligands. The regions of the brain where the δ-opioid receptor is largely expressed vary from species model to species model. In humans, the δ-opioid receptor is most heavily expressed in the basal ganglia and neocortical regions of the brain.
=== Stress === Smokers report higher levels of everyday stress. Several studies have monitored feelings of stress over time and found reduced stress after quitting. The deleterious mood effects of everyday between-cigarette nicotine withdrawal symptoms explain why people who smoke experience more daily stress than non-smokers, and become less stressed when they quit smoking. Deprivation reversal also explains much of the arousal data, with deprived smokers being less vigilant and less alert than non-deprived smokers or non-smokers. Recent studies have shown a positive relationship between psychological distress and salivary cotinine levels in smoking and non-smoking adults, indicating that both first-hand and second-hand smoke exposure may lead to higher levels of mental stress.
== External links == https://www.inf.ethz.ch/personal/gonnet/DarwinManual/node148.html https://web.expasy.org/docs/relnotes/relstat.html The most recent statistics from the Swiss-Prot protein knowledgebase. Section 6.1 contains the most up-to-date amino acid frequencies Sources of PAM matrices:
Sources: en.wikipedia.org
It is accepted practice to assume that if any symptom typical of DCS is present, that the diver has DCS and will be treated accordingly with recompression. Limited case data suggest that recompression does not usually cause harm if the differential diagnosis between IEBt vs IEDCS is doubtful.
Neoplasms – Renal cell carcinoma, liver tumors, Von Hippel–Lindau disease, and endocrine abnormalities including pheochromocytoma and adrenal adenoma with Cushing's syndrome. Anabolic steroid use – people whose testosterone levels are high, including athletes who abuse steroids, people on testosterone replacement for hypogonadism or transgender hormone replacement therapy. Blood doping – Athletes who take erythropoietin-stimulating agents or receive blood transfusions to increase their red blood cell mass. Post-transplant erythrocytosis – About 10–15% of patients after renal transplantation are found to have polycythemia at 24 months after transplantation, which can be associated with increased thrombotic (clotting) risk.
Cholesterol is implicated in cell signaling processes, assisting in the formation of lipid rafts in the plasma membrane, which brings receptor proteins in close proximity with high concentrations of second messenger molecules. In multiple layers, cholesterol and phospholipids (both electrical insulators) can facilitate speed of transmission of electrical impulses along nerve tissue. For many neuron fibers, a myelin sheath, rich in cholesterol since it is derived from compacted layers of Schwann cell or oligodendrocyte membranes, provides insulation for more efficient conduction of impulses. Demyelination (loss of myelin) is believed to be part of the basis for multiple sclerosis. Cholesterol binds to and affects the gating of a number of ion channels such as the nicotinic acetylcholine receptor, GABAA receptor, and the inward-rectifier potassium channel. Cholesterol activates the estrogen-related receptor alpha (ERRα) and may be the endogenous ligand for the receptor. The constitutively active nature of the receptor may be explained by the fact that cholesterol is ubiquitous in the body. Inhibition of ERRα signaling by reduction of cholesterol production has been identified as a key mediator of the effects of statins and bisphosphonates on bone, muscle, and macrophages. On the basis of these findings, it has been suggested that the ERRα should be de-orphanized and classified as a receptor for cholesterol.
In his normal life, he is a quiet programmer for the "respectable software company" Meta Cortex, while in private, he is a computer hacker who penetrates computer systems illicitly and steals information under his hacker alias "Neo". He also sells illegal untraceable computer systems and hacking programs along with controlling computer viruses stashed on CDs and diskettes. During his time as a hacker, Anderson has learned about something known only as "The Matrix". During the years prior to the events of The Matrix, Neo has spent his time trying to find the one man who he thought could tell him what the Matrix was, a supposed terrorist known only as Morpheus. After an encounter with another hacker, Trinity, Anderson is suddenly contacted by Morpheus via a cell phone mailed to his office, but is almost immediately captured by the virtual reality's Agents, led by Agent Smith. After refusing to cooperate with the agents, Neo has an electronic bug implanted within his Matrix-simulated body so that his actions can be tracked, and those seeking to make contact from the free world can be traced and destroyed. He is then contacted by Trinity, freed from the bug, and taken to meet Morpheus. Neo is offered a choice to remain in his everyday life and forget about the Matrix or to learn what the Matrix really is. Choosing the latter option, he takes a drug (commonly called the "red pill"), which is actually a program designed to disrupt his mind's neural connection to the Matrix and make it easier for his real body to be found and awakened in the real world.
== Function == Originating from the embryonic epidermis, the hair follicle evolves into one of the most complex structures in the human body, comprising 7–8 distinct tissue sections. The base of the hair follicle contains the bulb, housing dermal fibroblasts known as the dermal papilla, crucial for morphogenesis and the hair follicle's cyclic activity. Encircling these cells is the matrix cell region, the hair follicle's proliferative compartment, responsible for the formation of different follicle compartments (except the ORS) and the production of crucial structural elements of hair - hair keratins and associated proteins known as KAPs. Keratin is a crucial fibrous protein found in animals, constituting tough structures like hair, feathers, nails, and horns. It's classified based on tissue origin and sulfur content: soft keratins have lower sulfur, while hard keratins, found in hair and claws, contain more sulfur, creating a stronger structure. Keratins belong to two types - acidic Type I and neutral-basic Type II, further categorized into Type I a and b, and Type II a and b. The initial step in forming keratin is the alignment of type I and type II keratin polypeptides to create a heterodimer, which then aggregates into higher-order structural units. Similar to other intermediate filament subunit proteins, a prevalent secondary structure exists: a well-preserved, central alpha-helical domain made up of four coiled-coil segments along with non-helical end-terminal domains that vary in sequences and lengths [14].
Sources: en.wikipedia.org
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.
Afamelanotide is the linear analogue [Nle4-D-Phe7]-alpha-MSH, sometimes called melanotan I, while melanotan II is cyclic and carries three further substitutions. The two are distinct molecules and are not interchangeable in analytical testing.
Binding to the four melanocortin receptor subtypes is well documented in vitro. The relative contribution of each subtype to whole-body effects in humans is far less certain.
No regulatory agency has authorised melanotan-2 as a medicine for any indication. It circulates mainly as a research chemical or through unregulated channels. As a result, identity, purity and content are not independently guaranteed.