This is a working overview of melanogenesis, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-12-04. Anything still debated is marked as such rather than presented as settled.
Melanocortin receptors comprise five subtypes with distinct tissue distributions and functions. Melanotan-2 is described in the literature as a non-selective agonist that engages several of these subtypes, including MC1R, MC3R, MC4R, and MC5R. MC1R is the subtype most directly linked to melanin production in skin cells. Because the compound is not subtype-selective, its observed effects in experimental settings are generally attributed to activity across multiple receptor pathways rather than to a single target.
Melanotan-2 is a synthetic linear peptide built from seven amino acids arranged in a short chain. Its sequence is commonly written as Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-NH2, which includes a modified N-terminus and an amidated C-terminus. The molecule belongs to the melanocortin family and acts as a receptor agonist. Structural features such as the D-phenylalanine residue and the Nle substitution are associated with increased stability against enzymatic degradation relative to the natural parent peptide.
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.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C50H69N15O9 | Free base; salt forms differ |
| Molecular weight | Approximately 1024 g/mol | Calculated for the free base |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water and polar solvents | Poorly soluble in non-polar solvents |
| Typical storage | -20 degrees Celsius, dry, protected from light | Refers to the solid form |
Outside regulated medicine, melanotan II circulates through online vendors as a research chemical, often marketed for tanning. Products sold this way vary widely in purity, concentration, and labeling accuracy, and independent testing has documented discrepancies. Published reports describe both pigment effects and adverse reactions, including nausea, flushing, and darkening of existing moles. Long-term safety data are sparse, and no large controlled trial has established a risk profile. Questions about cumulative effects on melanocytes remain unresolved in the literature.
Melanotan II is a synthetic peptide analog modeled on alpha-melanocyte-stimulating hormone, a naturally occurring signaling peptide involved in pigmentation. Its structure is a cyclic heptapeptide containing two non-natural substitutions, norleucine at position four and D-phenylalanine at position seven. These modifications resist enzymatic breakdown and extend the molecule's activity relative to the native hormone. The compound binds melanocortin receptors and is studied mainly as a pharmacological tool rather than a therapeutic product. It has never received approval as a medicine in any major jurisdiction.
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 compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
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.
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.
Regulatory treatment varies between countries. Several national medicines agencies have classified the peptide as unapproved, and customs authorities in some jurisdictions seize shipments on that basis. A few jurisdictions channel supply through prescription-only frameworks that do not list the substance by name. Because the material circulates mainly through online vendors, composition and purity are rarely verified before sale. Surveys of unapproved peptide products have reported labels that did not match measured content in a substantial fraction of samples.
== Enzymes that use NADP(H) as a substrate == In 2018 and 2019, the first two reports of enzymes that catalyze the removal of the 2' phosphate of NADP(H) in eukaryotes emerged. First the cytoplasmic protein MESH1 (Q8N4P3), then the mitochondrial protein nocturnin were reported. Of note, the structures and NADPH binding of MESH1 (5VXA) and nocturnin (6NF0) are not related.
=== Eating disorders === The American Dietetic Association discussed that vegetarian diets may be more common among adolescents with eating disorders, indicating that vegetarian diets do not cause eating disorders, but rather "vegetarian diets may be selected to camouflage an existing eating disorder".
Pan pizza, baked in a pan with a crispy edge; "Stuffed crust" pizza, with the outermost edge wrapped around a cylinder of mozzarella cheese; "Hand-tossed", more like traditional pizzeria crusts; "Thin 'N Crispy", a thin, crisp dough which was Pizza Hut's original style; Dippin' Strips pizza, a pizza cut into small strips that can be dipped into a number of sauces; The P'Zone, a pizza-calzone hybrid with a marinara dipping sauce that comes in plain, Supremo, Meaty, and pepperoni; The Bigfoot pizza, its largest product; The Priazzo, a pie like pizza stuffed with pizza ingredients. The "stuffed crust" pizza was introduced on March 26, 1995. By the end of the year, it had become one of their most popular lines.
==== Muscle ==== Glycogen storage diseases that involve skeletal muscle typically have exercise-induced (dynamic) symptoms, such as premature muscle fatigue, rather than fixed weakness (static) symptoms. Differential diagnoses for glycogen storage diseases that involve fixed muscle weakness, particularly of the proximal muscles, would be an inflammatory myopathy or a limb-girdle muscular dystrophy. For those with exercise intolerance and/or proximal muscle weakness, the endocrinopathies should be considered. The timing of the symptoms of exercise intolerance, such as muscle fatigue and cramping, is important in order to help distinguish it from other metabolic myopathies such as fatty acid metabolism disorders. Problems originating within the circulatory system, rather than the muscle itself, can produce exercise-induced muscle fatigue, pain and cramping that alleviates with rest, resulting from inadequate blood flow (ischemia) to the muscles. Ischemia that often produces symptoms in the leg muscles includes intermittent claudication, popliteal artery entrapment syndrome, and chronic venous insufficiency. Diseases disrupting the neuromuscular junction can cause abnormal muscle fatigue, such as myasthenia gravis, an autoimmune disease. Similar, are Lambert–Eaton myasthenic syndrome (autoimmune) and the congenital myasthenic syndromes (genetic). Diseases can disrupt glycogen metabolism secondary to the primary disease.
Sources: en.wikipedia.org
The decay of 40K in Earth's mantle ranks third, after 232Th and 238U, in the list of sources of radiogenic heat. Less is known about the amount of radiogenic sources in Earth's outer and inner core, which lie below the mantle. It has been proposed, though, that significant core radioactivity (1–2 TW) may be caused by high levels of U, Th and K. Potassium-40 is the largest source of natural radioactivity in animals including humans. A 70 kg human body contains about 140 g (or 126 g) of potassium, hence about 140g × 0.0117% * (39.96/39.10) ≈ 16.7 mg of 40K; whose decay produces about 3,850 to 4,300 disintegrations per second (becquerel) continuously throughout the life of an adult person (and proportionally less in children). The normal potassium-40 concentration in the human body is equivalent to 55 Bq per kilogram, corresponding to an effective dose of 0.2 millisievert per year throughout the body. This is the largest source of internal radiation, followed by 0.12 mSv per year from the nuclides in the uranium and thorium decay series, and just 12 microsieverts per year from carbon-14.
This is normally achieved through regular blood tests, although continuous blood sugar testing equipment (Continuous Glucose Monitors or CGMs) are now becoming available which could help to refine this balancing act once widespread usage becomes common.
== External links == Synopsis of Chapter 5, Campbell & Reece, 2002 Lecture notes on the structure and function of macromolecules Archived 2009-03-26 at the Wayback Machine Several (free) introductory macromolecule related internet-based courses Archived 2011-07-18 at the Wayback Machine Giant Molecules! by Ulysses Magee, ISSA Review Winter 2002–2003, ISSN 1540-9864. Cached HTML version of a missing PDF file. Retrieved March 10, 2010. The article is based on the book, Inventing Polymer Science: Staudinger, Carothers, and the Emergence of Macromolecular Chemistry by Yasu Furukawa.
=== Research === Many aspects of academic research and industrial research such as in pharmaceuticals, health products, and many others relies on accurate water analysis to identify substances of potential use, to refine those substances and to ensure that when they are manufactured for sale that the chemical composition remains consistent. The analytical methods used in this area can be very complex and may be specific to the process or area of research being conducted and may involve the use of bespoke analytical equipment.
=== Deactivation === The bioactivity of calcitriol is terminated by hydroxylation at position 24 by vitamin D3 24-hydroxylase, coded for by gene CYP24A1, forming calcitetrol. Further metabolism yields calcitroic acid, an inactive water-soluble compound that is excreted in bile. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) share a similar but not identical mechanism of action. Metabolites produced by vitamin D2 are named with an er- or ergo- prefix to differentiate them from the D3-based counterparts (sometimes with a chole- prefix).
Sources: en.wikipedia.org
No. Melanotan-2 is manufactured synthetically. The naturally occurring peptide in the same family is alpha-melanocyte-stimulating hormone, which the body produces as part of normal endocrine and neural signalling.
Both are synthetic analogues derived from the same parent hormone. Reference descriptions usually characterise afamelanotide as more selective for the MC1R subtype, whereas melanotan-2 is reported to interact with a wider range of melanocortin receptors.
Early studies explored melanocortin signalling and pigmentation, which later led to informal use of the label tanning peptide. That label is not a regulatory category and does not imply approved status for any purpose.
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.