This is a working overview of LC-MS/MS, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-05-04. Anything still debated is marked as such rather than presented as settled.
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.
Melanotan II holds no marketing authorisation from the Food and Drug Administration, the European Medicines Agency, the UK Medicines and Healthcare products Regulatory Agency or Australia's Therapeutic Goods Administration. Products sold under that name are treated as unapproved new drugs, and their sale or import is prohibited in several jurisdictions. Other countries classify the peptide as a prescription-only medicine or place it among controlled substances, so the legal position changes with the destination market. No pharmacopoeial monograph supplies an official specification, because the material is not a licensed pharmaceutical. Consequently, products offered online are not manufactured to a shared public standard.
The peer-reviewed record is dominated by small early-phase studies, case reports and pharmacovigilance summaries rather than large randomised trials. Papers typically examine tanning response, receptor selectivity or patterns of reported adverse events. Many note that participants obtained the peptide outside a clinical setting, which limits verification of composition and administered amount. Reported events vary widely, and causality is frequently unclear because the identity and purity of self-sourced material are unknown. Open questions include whether repeated melanocortin receptor stimulation produces cumulative effects, and how often label claims match actual content.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Free base; salt forms add to total mass |
| Molecular mass | About 1024 daltons | Calculated for the free base |
| Structural class | Cyclic heptapeptide | Contains D-phenylalanine and norleucine |
| Parent hormone | Alpha-melanocyte-stimulating hormone | Endogenous tridecapeptide of 13 residues |
| Receptor profile | Non-selective melanocortin agonist | Interacts with MC1R, MC3R, MC4R and MC5R |
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-2 has not received marketing authorisation from major regulatory agencies for any therapeutic indication. Several jurisdictions classify it as a prescription-only medicine or a controlled substance when supplied for human use. Because approved products do not exist, material sold online usually sits outside pharmaceutical supply chains and formal quality oversight. Regulators have issued public notices describing the compound as unapproved. Enforcement varies, and the legal position differs between countries, which complicates any single general statement about its status.
Scientific discussion of Melanotan-2 spans pharmacology, dermatology, and public-health literature. Laboratory studies examine its receptor binding and cellular effects, while clinical reports describe outcomes observed after unregulated use. These two bodies of work differ in rigour and intent. Peer-reviewed trials of the compound as a medicine are limited, so much of the available information comes from case reports and surveillance data. Authors frequently note the gap between experimental findings and real-world use.
The restaurants serve Korean food, including kimchi dishes, Pyongyang cold noodles, barbecued cuttlefish and dog meat soup. Patrons may also buy North Korean products such as ginseng wine and an unlabelled aphrodisiac claimed to be made from bears. The prices are relatively high and in US dollars. The staff consists of young Korean women in traditional Chosŏn-ot dress, who also perform karaoke as well as song and dance routines in the style of the North Korean Mass Games for the customers. Staff from North Korea typically work on three-year contracts, and are often highly trained graduates of arts colleges. Photography is generally not permitted inside.
== History == The existence of a compensatory mechanism for telomere shortening was first found by Soviet biologist Alexey Olovnikov in 1973, who also suggested the telomere hypothesis of aging and the telomere's connections to cancer and perhaps some neurodegenerative diseases. Telomerase in the ciliate Tetrahymena was discovered by Carol W. Greider and Elizabeth Blackburn in 1984. Together with Jack W. Szostak, Greider and Blackburn were awarded the 2009 Nobel Prize in Physiology or Medicine for their discovery. Later the cryo-EM structure of telomerase was first reported in T. thermophila, to be followed a few years later by the cryo-EM structure of telomerase in humans. The role of telomeres and telomerase in cell aging and cancer was established by scientists at biotechnology company Geron with the cloning of the RNA and catalytic components of human telomerase and the development of a polymerase chain reaction (PCR) based assay for telomerase activity called the TRAP assay, which surveys telomerase activity in multiple types of cancer. The negative stain electron microscopy (EM) structures of human and Tetrahymena telomerases were characterized in 2013. Two years later, the first cryo-electron microscopy (cryo-EM) structure of telomerase holoenzyme (Tetrahymena) was determined. In 2018, the structure of human telomerase was determined through cryo-EM by UC Berkeley scientists.
=== 1890s === 1890: Austrian-born chemist Ida Freund became the first woman to work as a university chemistry lecturer in the United Kingdom. She was promoted to full lecturer at Newnham College, Cambridge. 1890: British popular science educator and author Agnes Giberne co-founded the British Astronomical Association. Subsequently, English astronomer Elizabeth Brown was appointed the director of the association's Solar Section, well known for her studies in sunspots and other solar phenomena. 1890: British mathematician Philippa Fawcett became the first woman to obtain the highest score in the Cambridge Mathematical Tripos examinations, a score "above the Senior Wrangler". (At the time, women were ineligible to be named Senior Wrangler.) 1891: American-born astronomer Dorothea Klumpke was appointed as Head of the Bureau of Measurements at the Paris Observatory. For the next decade, in addition to completing her doctorate of science, she worked on the Carte du Ciel mapping project. She was recognized for her work with the first Prix de Dames award from the Société astronomique de France and named an Officier of the Paris Academy of Sciences. 1892: American psychologist and logician Christine Ladd-Franklin presented her evolutionary theory on the development of colour vision to the International Congress of Psychology. Her theory was the first to emphasize colour vision as an evolutionary trait. 1893: Florence Bascom became the second woman to earn her PhD in geology in the United States, and the first woman to receive a PhD from Johns Hopkins University.
Sources: en.wikipedia.org
A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal. An important concept in check valves is the cracking pressure which is the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.
== External links == amylin at the U.S. National Library of Medicine Medical Subject Headings (MeSH) "Amylin Nucleation Site". PDB Entry 1KUW. RCSB Protein Data Bank. doi:10.2210/pdb1kuw/pdb. Archived from the original on 16 April 2008. Retrieved 2008-05-28. Human DAP genome location and DAP gene details page in the UCSC Genome Browser. Human IAPP genome location and IAPP gene details page in the UCSC Genome Browser.
Subsequent research has found that the delayed dopaminergic phase is associated with the highly potent dopamine D4 receptor agonism of LSD's metabolite 13-hydroxy-LSD. The first phase is described as a "psychedelic experience", with "meaningfulness and portentousness" as the primary effects, while the latter phase is "clearly a paranoid state", including feeling "at the least self-centered, and usually suspicious, with ideas of reference or even paranoid convictions". The second phase typically develops about 4 to 6 hours after administration but at times up to 10 hours after administration. Parallels have been drawn between this phase and amphetamine psychosis. There is no indication that similar effects occur with other psychedelics like phenethylamines and simple tryptamines, which lack dopamine receptor agonism. The preceding findings have been described by researchers like Daniel X. Freedman and David E. Nichols.
Sources: en.wikipedia.org
For each essential amino acid i, calculate Ti/Ri. Take the amino acid with the smallest value of Ti/Ri. Call it l. This is the limiting amino acid. The AAS is 100% × Tl/Rl. PDCAAS estimates digestibility in a separate procedure. The estimated PD is multiplied with AAS to get PDCAAS.
=== Biochemical and biomedical roles === Sulfur dioxide or its conjugate base bisulfite is produced biologically as an intermediate in both sulfate-reducing organisms and in sulfur-oxidizing bacteria, as well. The role of sulfur dioxide in mammalian biology is not yet well understood. Sulfur dioxide blocks nerve signals from the pulmonary stretch receptors and abolishes the Hering–Breuer inflation reflex. It is considered that endogenous sulfur dioxide plays a significant physiological role in regulating cardiac and blood vessel function, and aberrant or deficient sulfur dioxide metabolism can contribute to several different cardiovascular diseases, such as arterial hypertension, atherosclerosis, pulmonary arterial hypertension, and stenocardia. It was shown that in children with pulmonary arterial hypertension due to congenital heart diseases the level of homocysteine is higher and the level of endogenous sulfur dioxide is lower than in normal control children. Moreover, these biochemical parameters strongly correlated to the severity of pulmonary arterial hypertension. Authors considered homocysteine to be one of useful biochemical markers of disease severity and sulfur dioxide metabolism to be one of potential therapeutic targets in those patients. Endogenous sulfur dioxide also has been shown to lower the proliferation rate of endothelial smooth muscle cells in blood vessels, via lowering the MAPK activity and activating adenylyl cyclase and protein kinase A.
Pocket watch movements are occasionally engraved with the word "Adjusted", or "Adjusted to n positions". This means that the watch has been tuned to keep time under various positions and conditions. There are eight possible adjustments:
Sources: en.wikipedia.org
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.
Melanotan-1, also called afamelanotide, is a linear analogue with greater selectivity for MC1R and has received approval in some jurisdictions for a specific photosensitivity disorder. Melanotan-2 is cyclic, less selective, and reaches central receptors more readily. The two are often confused in online discussion despite different pharmacology and regulatory status.
Alpha-MSH is an endogenous tridecapeptide derived from pro-opiomelanocortin. Melanotan-2 reproduces its core receptor-binding sequence inside a shortened, stabilised ring. The result is a molecule with a longer effective half-life and higher potency than the parent hormone.
Regulatory treatment varies by country. In the United States, the European Union and Australia it is an unapproved drug and its sale is restricted, while some other jurisdictions list it as prescription-only or controlled. The applicable rules depend on the country of import.