lactam bridge comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-06-23. Where a claim depends on a specific study, the study is described rather than over-claimed.
Melanotan-2 is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence incorporates a lactam bridge that constrains the peptide into a ring, which increases resistance to enzymatic breakdown relative to the natural hormone. Researchers at the University of Arizona synthesised the compound in the late 1980s and early 1990s while studying pigmentation pathways. It has never received marketing approval from any national medicines regulator. In the scientific literature it is usually described as a laboratory research reagent rather than a therapeutic product.
The peptide acts as a non-selective agonist at melanocortin receptors, showing affinity for MC1R, MC3R, MC4R and MC5R. Activation of MC1R on melanocytes drives the conversion of tyrosine into melanin and shifts production toward the darker eumelanin form. MC4R signalling in the central nervous system is linked to appetite and energy balance, which helps explain why reduced food intake appeared in early human studies. Effects on MC4R and on vascular tone also account for the erectile responses recorded as unexpected findings in those same trials.
Melanotan-2 is frequently confused with afamelanotide, a linear analogue authorised in the European Union for erythropoietic protoporphyria. The two compounds differ in chain length, ring structure and receptor selectivity, so findings for one cannot be transferred directly to the other. Published controlled human data on melanotan-2 remain sparse, and much of what circulates online derives from small studies or unpublished reports. Questions about effect size, dose-response behaviour and long-term safety therefore remain unresolved.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Alpha-MSH analogue with a lactam ring |
| Molecular formula | C50H69N15O9 | Commonly cited value for the neutral peptide |
| Molecular weight | 1024.18 g/mol | Calculated for the free molecule |
| Appearance | White to off-white powder | Typically supplied as a lyophilised solid |
| Solubility | Soluble in water, DMSO and ethanol | Dissolution in pure water is often slow |
In those on insulin, routinely checking blood sugar levels (such as through a continuous glucose monitor) is advised; however, this may not be needed in those who are not on insulin therapy. Bariatric surgery often improves diabetes in those who are obese. Rates of type 2 diabetes have increased markedly since 1960 in parallel with obesity. As of 2015, there were approximately 392 million people diagnosed with the disease compared to around 30 million in 1985. Typically, it begins in middle or older age, although rates of type 2 diabetes are increasing in young people. Type 2 diabetes is associated with a ten-year-shorter life expectancy. Diabetes was one of the first diseases ever described, dating back to an Egyptian manuscript from c. 1500 BCE. Two types of diabetes were identified in 400–500 CE, one type associated with youth (now identified as type 1) and the other associated with being overweight (now identified as type 2). The importance of insulin in the disease was determined in the 1920s.
=== Reactions of strained alkenes === Strained alkenes also use strain-relief as a driving force that allows for their participation in click reactions. Trans-cycloalkenes (usually cyclooctenes) and other strained alkenes such as oxanorbornadiene react in click reactions with a number of partners including azides, tetrazines, and tetrazoles. These reaction partners may interact specifically with the strained alkene, staying bioorthogonal to endogenous alkenes found in lipids, fatty acids, cofactors, and other natural products.
Political developments in the Soviet Union included Stalin dismantling the remaining elements of democracy from the party by extending his control over its institutions and eliminating any possible rivals. The party's ranks grew in numbers, with the party modifying its organisation to include more trade unions and factories. The ranks and files of the party were populated with members from the trade unions and the factories, whom Stalin controlled because there were no other Old Bolsheviks to contradict Marxism–Leninism. In the late 1930s, the Soviet Union adopted the 1936 Soviet Constitution which ended weighted-voting preferences for workers, promulgated universal suffrage for every man and woman older than 18 years of age and organised the soviets (councils of workers) into two legislatures, namely the Soviet of the Union (representing electoral districts) and the Soviet of Nationalities (representing the ethnic groups of the country). By 1939, with the exception of Stalin himself, none of the original Bolsheviks of the October Revolution of 1917 remained in the party. Unquestioning loyalty to Stalin was expected by the regime of all citizens. Stalin exercised extensive personal control over the party and unleashed an unprecedented level of violence to eliminate any potential threat to his regime. While Stalin exercised major control over political initiatives, their implementation was in the control of localities, often with local leaders interpreting the policies in a way that served themselves best.
== Function == As its name suggests, NGF is involved primarily in the growth, as well as the maintenance, proliferation, and survival of nerve cells (neurons) and is critical for the survival and maintenance of sympathetic and sensory neurons as they undergo apoptosis in its absence. However, several recent studies suggest that NGF is also involved in pathways besides those regulating the life cycle of neurons.
Sources: en.wikipedia.org
== Habitat and ecology == N. tabacum is a native of tropical and subtropical America, also appearing as a weed. N. tabacum is sensitive to temperature, air, ground humidity and the type of land. Temperatures of 20–30 °C (68–86 °F) are best for adequate growth; an atmospheric humidity of 80-to-85% and soil without a high level of nitrogen are also optimal.
== Research == Flunarizine may help to reduce the severity and duration of attacks of paralysis associated with the more serious form of alternating hemiplegia, as well as being effective in rapid onset dystonia-parkinsonism (RDP). Both these conditions arise from specific mutations in the ATP1A3 gene. Flunarizine extended motor neuron survival in spinal cord, protected skeletal muscles from cell death and atrophy and extended survival by 40% in an animal model of spinal muscular atrophy. Flunarizine has also shown promise as an anti-prion medication.
Until the collapse of the federal government in 1991, the organisational and administrative structure of Somalia's healthcare sector was overseen by the Ministry of Health. Regional medical officials enjoyed some authority, but healthcare was largely centralised. The socialist government of former President of Somalia Siad Barre had put an end to private medical practice in 1972. Much of the national budget was devoted to military expenditure, leaving few resources for healthcare, among other services. Somalia's public healthcare system was largely destroyed during the ensuing civil war. As with other previously nationalised sectors, informal providers have filled the vacuum and replaced the former government monopoly over healthcare, with access to facilities witnessing a significant increase. Many new healthcare centres, clinics, hospitals and pharmacies have in the process been established through home-grown Somali initiatives. The cost of medical consultations and treatment in these facilities is low, at US$5.72 per visit in health centres (with a population coverage of 95%), and US$1.89–3.97 per outpatient visit and US$7.83–13.95 per bed day in primary through tertiary hospitals. Comparing the 2005–2010 period with the half-decade just prior to the outbreak of the conflict (1985–1990), life expectancy actually increased from an average of 47 years for men and women to 48.2 years for men and 51 years for women.
== Pan-Slavism in Russia == During the time of the Soviet Union, Bolshevik teachings viewed Pan-Slavism as a reactionary element associated to the Russian Empire. As a result, Bolsheviks viewed it as contrary to their Marxist ideology. Pan-Slavists even faced persecution during the Stalinist repressions in the Soviet Union (see Slavists case). Nowadays, ultranationalist parties like the Russian National Unity party advocate for a Russian-dominated 'Slavic Union'.
== Further reading == papuamide Ford, PW; Gustafson, KR; McKee, TC; Shigematsu, N; Maurizi, LK; Pannell, LK; Williams, DE; de Silva, ED; Lassota, P; Allen, TM; Van Soest, R; Andersen, RJ; Boyd, MR (1999). "Papuamides A-D, HIV-Inhibitory and Cytotoxic Depsipeptides from the Sponges Theonella mirabilis and Theonella swinhoei Collected in Papua New Guinea". J. Am. Chem. Soc. 121 (25): 5899–5909. Bibcode:1999JAChS.121.5899F. doi:10.1021/ja990582o. neamphamide A Oku, N; Gustafson, KR; Cartner, LK; Wilson, JA; Shigematsu, N; Hess, S; Pannell, LK; Boyd, MR; McMahon, JB (2004). "Neamphamide A. A new HIV-inhibitory depsipeptide from the Papua New Guinea marine sponge Neamphius huxleyi". J. Nat. Prod. 67 (8): 1407–11. Bibcode:2004JNAtP..67.1407O. doi:10.1021/np040003f. PMID 15332865. callipeltin A Zampella, A; D'Auria, MV; Paloma, LG; Casapullo, A; Minale, L; Debitus, C; Henin, Y (1996). "Callipeltin A, an Anti-HIV Cyclic Depsipeptide from the New Caledonian Lithistida Sponge Callipelta sp.". J. Am. Chem. Soc. 118 (26): 6202–9. Bibcode:1996JAChS.118.6202Z. doi:10.1021/ja954287p. mirabamides A-D Plaza, A; Gustchina, E; Baker, HL; Kelly, M; Bewley, CA (2007). "Mirabamides A-D. Depsipeptides from the sponge Siliquariaspongia mirabilis that inhibit HIV-1 fusion". J. Nat. Prod. 70 (11): 1753–60. Bibcode:2007JNAtP..70.1753P. doi:10.1021/np070306k. PMID 17963357.; Andjelic, CD; Planelles, V; Barrows, LR (2008). "Characterizing the Anti-HIV Activity of Papuamide A." Mar Drugs. 6 (4): 528–49. doi:10.3390/md20080027. PMC 2630844. PMID 19172193.
Sources: en.wikipedia.org
Feminizing hormone therapy, also known as transfeminine hormone therapy, is a form of gender-affirming hormone therapy (GAHT) which change the primary and secondary sex characteristics of transgender people from masculine to feminine. It is one of the two common type of GAHT the other being masculinizing hormone therapy) and is used to treat transgender women and non-binary transfeminine individuals. Some others, in particular intersex people, but also some non-transgender people, take this form of therapy according to their personal needs and preferences. The purpose of the therapy is to cause the development of the secondary sex characteristics of the desired sex, such as breasts and a feminine pattern of hair, fat, and muscle distribution. It cannot undo many of the changes produced by naturally occurring puberty, which may necessitate surgery and other treatments to reverse (see below). The medications used for feminizing hormone therapy include estrogens, antiandrogens, progestogens, and gonadotropin-releasing hormone modulators (GnRH modulators). Feminizing hormone therapy has been empirically shown to reduce the distress and discomfort associated with gender dysphoria in transfeminine individuals.
(2026) reconstruct the demographic history of late Neanderthals on the basis of data from mitochondrial DNA, reporting evidence indicating that nearly all late Neanderthals from Europe belonged to a single mitochondrial DNA lineage, likely as a result of expansion across Europe from a refugium in southwestern France, and evidence of rapid decline in the effective population size of late Neanderthals shortly before their extinction; Sánchez Goñi & d'Errico (2026) link the presence of the refugium in southwestern France to the climatic configuration affecting western Europe 76,000 to 68,000 years ago. Bossoms Mesa et al. (2026) reconstruct the genetic diversity of late Neanderthals from Belgium and France, finding no evidence of mating among close relatives or genetic deterioration prior to Neanderthal extinction. Yousefi et al. (2026) study changes in suitability and connectivity of Neanderthal habitat through time, and find no evidence of habitat fragmentation caused by climate changes before Neanderthal extinction. Baykara et al. (2026) report evidence of sequential occupation of the Üçağızlı II Cave (Turkey) by Neanderthals and modern humans, and evidence of cultural continuity between members of the two human lineages occupying the site. Schoenemann et al. (2026) interpret differences in brain anatomy of Neanderthals and modern humans as falling within the range of differences between modern human populations, and find no evidence of significang cognitive differences between Neanderthals and modern humans that might have contributed to Neanderthal extinction.
=== IATSE strike === Problems kept coming on July 16, when thirty to thirty-five crew members went on strike to demand better wages and benefits, under encouragement from the IATSE union, whose local representative warned that the dispute would cost The Stone Group an additional $40,000 per day. The production was sanctioned by the Directors Guild of America and Screen Actors Guild, but did not recognize other labor groups. As such, the film's technicians were signed to a flat fee. Filming was again suspended but, since Mississippi was a right-to-work state, the concerned workers were summarily fired and fifty new ones were brought in. This included cinematographer Leonetti, who was replaced by Alexander Gruszynski and complained that he stood to lose $50,000 in wages. Meanwhile, on July 17, Bosworth was officially released from his NFL contract by the Seattle Seahawks, although this was expected due to his persistent shoulder issues, and he already considered himself an actor first.
Paul Berg, a Nobel laureate in chemistry, wrote to the Senate that "Quackery will always prey on the gullible and uninformed, but we should not provide it with cover from the NIH," and called the office "an embarrassment to serious scientists". Allen Bromley, then-president of the American Physical Society, similarly wrote to Congress that the OAM had "emerged as an undiscriminating advocate of unconventional medicine. It has bestowed the considerable prestige of the NIH on a variety of highly dubious practices, some of which clearly violate basic laws of physics". Leon Jaroff, writing for The New York Times in 1997, described the OAM as "Tom Harkin's folly". In 1995, Wayne Jonas, a promoter of homeopathy and political ally of Harkin, became the director of the OAM, and continued in that role until 1999. In 1997, the NCCAM budget was increased from $12 million to $20 million annually. From 1990 to 1997, use of alternative medicine in the US increased by 25%, with a corresponding 50% increase in expenditures. The OAM drew increasing criticism from eminent members of the scientific community with letters to the Senate Appropriations Committee when discussion of renewal of funding OAM came up. In 1998, the President of the North Carolina Medical Association publicly called for shutting down the OAM. In 1998, NIH director and Nobel laureate Harold Varmus came into conflict with Harkin by pushing to have more NIH control of alternative medicine research. The NIH Director placed the OAM under stricter scientific NIH control.
Four members of 2A peptides family are frequently used in life science research. They are P2A, E2A, F2A, and T2A. F2A is derived from foot-and-mouth disease virus 18; E2A is derived from equine rhinitis A virus; P2A is derived from porcine teschovirus-1 2A; T2A is derived from thosea asigna virus 2A. The following table shows the sequences of four members of 2A peptides. Adding the optional linker “GSG” (Gly-Ser-Gly) on the N-terminal of a 2A peptide greatly helps with efficiency. 2A peptides trigger the ribosome to skip peptide bond formation between the glycine (G) and proline (P) near the C-terminus of the 2A peptide, resulting in the peptide located upstream of the 2A peptide having extra amino acids appended to its C-terminus while the protein downstream the 2A peptide will have an extra proline on its N-terminus. The exact molecular mechanism of 2A-peptide-mediated cleavage is still unknown. However, it is believed to involve ribosomal "skipping" of glycyl-prolyl peptide bond formation rather than true proteolytic cleavage.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide modelled on alpha-melanocyte-stimulating hormone. A lactam bridge links two side chains, forming a ring that stabilises the molecule against proteolysis. It belongs to the broader melanocortin peptide family.
No national medicines agency has approved melanotan-2 for clinical use. Afamelanotide, a related but distinct peptide, holds a marketing authorisation in the European Union for a rare photosensitivity disorder. Melanotan-2 itself is handled as a laboratory chemical.
Its broad activity across melanocortin receptors makes it a tool for probing pigmentation, appetite and vascular signalling. Early trials recorded skin darkening and other effects that were not the original focus of the work. Those observations generated hypotheses that later studies have examined.
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.