If you have been reading about melanocortin receptors 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 2025-09-27. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| 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 |
Protect the body's internal living tissues and organs Protect against invasion by foreign organisms, including infectious organisms Protect the body from dehydration Protect the body against abrupt changes in temperature, maintain homeostasis Help excrete waste materials through perspiration Act as a receptor for touch, pressure, pain, heat, and cold (see Somatosensory system) Protect the body against sunburns by secreting melanin Generate vitamin D through exposure to ultraviolet light Store water, fat, glucose, vitamin D Maintenance of the body form Formation of new cells from stratum germinativum to repair minor injuries Protect from UV rays. Regulates body temperature It distinguishes, separates, and protects the organism from its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.
=== General and cited sources === Belladelli, Federico; Del Giudice, Francesco; Glover, Frank; Mulloy, Evan; Muncey, Wade; Basran, Satvir; Fallara, Giuseppe; Pozzi, Edoardo; Montorsi, Francesco; Salonia, Andrea; Eisenberg, Michael L. (2023). "Worldwide Temporal Trends in Penile Length: A Systematic Review and Meta-Analysis". The World Journal of Men's Health. 41 (4): 848–860. doi:10.5534/wjmh.220203. PMC 10523114. PMID 36792094. "Men worry more about penile size than women, says 60-year-old research review" (Press release). Blackwell. 31 May 2007. Archived from the original on 21 April 2021. Retrieved 11 August 2018. Cakir, Omer Onur; Pozzi, Edoardo; Castiglione, Fabio; Alnajjar, Hussain M.; Salonia, Andrea; Muneer, Asif (March 2021). "Penile Length Measurement: Methodological Challenges and Recommendations, a Systematic Review". The Journal of Sexual Medicine. 18 (3): 433–439. doi:10.1016/j.jsxm.2020.11.012. PMID 33648901. Lauersen, Niels; Whitney, Steven (1983). It's Your Body: A Woman's Guide to Gynecology (3rd ed.). New York: Berkley Publishing. p. 480. ISBN 978-0-425-09917-9. Lee, P. A; Mazur, T; Danish, R; Amrhein, J; Blizzard, R. M; Money, J; Migeon, C. J (1980). "Micropenis. I. Criteria, etiologies and classification". The Johns Hopkins Medical Journal. 146 (4): 156–63. PMID 7366061. NAID 10010056499. Loos, Shirley; De Wil, Peter; Delcarte, Leslie; Serefoglu, Ege Can; Van Renterghem, Koenraad; Ward, Sam (September 2023). "The effect of penis size on partner sexual satisfaction: a literature review". International Journal of Impotence Research. 35 (6): 519–522.
=== Medication === Gynecomastia can respond well to medical treatment, although it is usually effective only when done within the first two years after the start of male breast enlargement. Selective estrogen receptor modulators (SERMs) such as tamoxifen, raloxifene, and clomifene may be beneficial in the treatment of gynecomastia but are not approved by the Food and Drug Administration for use in gynecomastia. Clomifene seems to be less effective than tamoxifen or raloxifene. Tamoxifen may be used to treat gynecomastia in adults, and of the medical treatments used, tamoxifen is the most effective. Recent studies have shown that treatment with tamoxifen may represent a safe and effective mode of treatment in cases of cosmetically disturbing or painful gynecomastia. Aromatase inhibitors (AIs) such as anastrozole have been used off-label for cases of gynecomastia occurring during puberty but are less effective than SERMs. A few cases of gynecomastia caused by the rare disorders aromatase excess syndrome and Peutz–Jeghers syndrome have responded to treatment with AIs such as anastrozole. Androgens/anabolic steroids may be effective for gynecomastia. Testosterone itself may not be suitable to treat gynecomastia as it can be aromatized into estradiol, but nonaromatizable androgens like topical androstanolone (dihydrotestosterone) can be useful.
=== Sclerodactyly === Though it is the most easily recognizable manifestation, it is not prominent in all patients. Thickening generally only involves the skin of the fingers distal to the metacarpophalangeal joints in CREST. Early in the course of the disease, the skin may appear edematous and inflamed. Eventually, dermal fibroblasts overproduce extracellular matrix leading to increased tissue collagen deposition in the skin. Collagen cross-linking then causes a progressive skin tightening. Digital ischemic ulcers commonly form on the distal fingers in 30–50% of patients.
Carbohydrates are usually present, often in a mix of simple sugars like glucose and more complex oligosaccharides such as maltodextrin which are supposed to provide more sustained energy. Carbohydrates cause an increase in serotonin levels. These are used both to provide a sweet taste and fuel for exercise, though evidence for whether they actually enhance exercise performance is mixed. Protein supplements, usually in a palatable powdered form such as whey protein or rice protein, are also commonly used both for flavour and as a fuel for muscle growth and recovery. Electrolytes providing sodium, potassium and magnesium (and often others such as zinc, calcium, iron etc in smaller amounts) are often included to replace those lost due to sweating during heavy exercise, generally as a mixture of different salts, sometimes including exotic forms such as zinc monomethionine aspartate or calcium fructoborate which are supposed to be better absorbed or have other special properties. Electrolytes help the body perform homeostasis and prevent dehydration. Nitrate salts are commonly included (often as "beetroot extract") for their supposed benefits for endurance exercise. Sometimes this is achieved by using nitrate salts of other ingredients (e.g. arginine nitrate, creatine nitrate). Creatine, a natural chemical created in the kidneys and liver, is used supposedly to improve physical performance. It also promotes an increase in muscle growth. β-Alanine is a common ingredient found in 87% of leading pre-workout formulas.
Sources: en.wikipedia.org
The oxygenase reaction of RuBisCO may prevent CO2 depletion near its active sites and contributes to the regulation of CO2 concentration in the atmosphere The photorespiratory pathway is a major source of hydrogen peroxide (H2O2) in photosynthetic cells. Through H2O2 production and pyrimidine nucleotide interactions, photorespiration makes a key contribution to cellular redox homeostasis. In so doing, it influences multiple signalling pathways, in particular, those that govern plant hormonal responses controlling growth, environmental and defense responses, and programmed cell death. It has been postulated that photorespiration may function as a "safety valve", preventing the excess of reductive potential coming from an overreduced NADPH-pool from reacting with oxygen and producing free radicals (oxidants), as these can damage the metabolic functions of the cell by subsequent oxidation of membrane lipids, proteins or nucleotides. The mutants deficient in photorespiratory enzymes are characterized by a high redox level in the cell, impaired stomatal regulation, and accumulation of formate.
The brisket muscles are sometimes separated for retail cutting: the lean "first cut" or "flat cut" is the deep pectoral, while the fattier "second cut", "point", "fat end", or "triangular cut" is the superficial pectoral. For food service use, they are IMPS 120A and 120B, respectively.
The motor proteins actin and myosin generate the forces exerted by contracting muscles. Cortisol decreases amino acid uptake by muscle and inhibits protein synthesis. Current recommendations suggest that bodybuilders should consume 25–30% of protein per total calorie intake to further their goal of maintaining and improving their body composition. This is a widely debated topic, with many arguing that 1 gram of protein per pound of body weight per day is ideal, some suggesting that less is sufficient, while others recommending 1.5, 2, or more. It is believed that protein needs to be consumed frequently throughout the day, especially during/after a workout, and before sleep. There is also some debate concerning the best type of protein to take. Chicken, turkey, beef, pork, fish, eggs and dairy foods are high in protein, as are some nuts, seeds, beans, and lentils. Casein or whey are often used to supplement the diet with additional protein. Whey is the type of protein contained in many popular brands of protein supplements and is preferred by many bodybuilders because of its high biological value (BV) and quick absorption rates. Whey protein also has a bigger effect than casein on insulin levels, triggering about double the amount of insulin release. That effect is somewhat overcome by combining casein and whey.
The acyl carrier protein (ACP), aryl carrier protein (ArCP), and the peptidyl carrier protein (PCP) are a family of protein cofactors that participate in fatty acid (acyl), polyketide (acyl and aryl), and nonribosomal peptide (peptidyl) biosynthesis. The growing molecule is bound to the A(r)/PCP via a thioester derived from the distal thiol of a 4'-phosphopantetheine (PPant) moiety. A(r)/PCPs are found in bacteria and eukaryotes (including humans) alike. The E. coli version (EcacpP) is the best studied. In E. coli, the ACP is one of the most abundant cytosolic proteins at 0.25% of the total soluble protein (by molecule count). It is small, very acidic, and very soluble. EcacpP works as a cofactor in the synthesis of both long and short chain fatty acids in the bacterium. It interacts with fatty acid synthase proteins that "flips" the growing fatty acid chain out of the ACP's internal cavity and modifies it. This kind of setup where the ACP exists as a free-floating protein is called Type II. An alternative is the Type I system, where a large protein contains several synthase domains as well as its own ACP domain. The ACP domain is pass around by the synthase domains to build a molecule. Polyketide synthases and nonribosomal peptide synthetases interact with their carrier proteins in a similar way. There is a similar distinction in how they are organized into type I and type II. Plant ACPs participate in the biosynthesis of fatty acids, exploited by humans in the form of vegetable oils.
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.
It is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, containing seven amino acids with a lactam ring and a D-configured phenylalanine residue. It is supplied as a lyophilised powder for laboratory research.