The short version of Aib substitution fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-07-26. Anything still debated is marked as such rather than presented as settled.
Semaglutide is a synthetic peptide analog of human glucagon-like peptide-1, a gut hormone released after meals. Its backbone retains the GLP-1 sequence but incorporates two substitutions that slow enzymatic breakdown by dipeptidyl peptidase-4. A short polyethylene glycol linker and a C18 fatty diacid are attached to the peptide chain, allowing the molecule to bind serum albumin and remain in circulation far longer than the native hormone. The result is a circulating half-life measured in days rather than the minutes typical of endogenous GLP-1.
Receptor activation occurs at GLP-1 receptors distributed across pancreatic islets, the hypothalamus, and the gastrointestinal tract. Binding triggers G protein signaling that raises cyclic AMP and enhances glucose-dependent insulin release. Because the effect depends on prevailing glucose levels, insulin secretion does not rise when blood sugar is already low. Signaling in the brain and gut also influences appetite and gastric emptying, which is why the compound appears in both metabolic and weight-related research literature.
Three structural changes define the molecule. At position 8 an alpha-aminoisobutyric acid residue replaces alanine, which blocks dipeptidyl peptidase-4 cleavage. At position 34 arginine replaces lysine, and at position 26 a lysine carries a C18 fatty diacid attached through a short linker. The fatty chain binds serum albumin, and this albumin association reduces renal filtration and enzymatic attack. The unchanged backbone retains the receptor contacts that produce signalling. The free base has the formula C187H291N45O59 and a molecular weight near 4114 daltons.
Receptor activation follows the canonical Gs pathway: binding increases intracellular cyclic AMP, which promotes protein kinase A activity. In pancreatic beta cells this amplifies glucose-dependent insulin release, so secretion rises when blood glucose is high and changes little when it is low. The same signalling suppresses glucagon release from alpha cells and slows gastric emptying. Receptors in the hypothalamus and brainstem are thought to contribute to reduced appetite and lower energy intake. Which of these effects dominates clinical outcomes remains an area of active study.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic peptide, GLP-1 receptor agonist | Not a small molecule |
| Backbone substitutions | Non-natural residue at position 8, arginine at position 34 | Slows enzymatic cleavage |
| Side chain | C18 fatty diacid with PEG linker | Enables albumin binding |
| Approximate molecular mass | 4114 Da | Varies slightly with salt form |
| Reported half-life | About one week | Longer than native GLP-1 by orders of magnitude |
Clinical studies of semaglutide generally measure glycated hemoglobin, fasting plasma glucose, body weight, and composite cardiovascular endpoints. The SUSTAIN program enrolled adults with type 2 diabetes, while the STEP program focused on obesity without diabetes. Administration follows a stepwise escalation schedule designed to limit gastrointestinal effects during the first weeks. Reported outcomes include mean percentage weight change, the proportion of participants reaching defined weight-loss thresholds, and rates of nausea, vomiting, and diarrhea. Long-term data on durability after treatment stops are still limited and remain a topic of ongoing research.
Semaglutide is a synthetic peptide analog of human glucagon-like peptide-1, developed by Novo Nordisk and first approved in 2017 for type 2 diabetes. It belongs to the incretin mimetic class, a group of agents that reproduce the glucose-dependent actions of endogenous GLP-1. The molecule was engineered to resist degradation by dipeptidyl peptidase-4 and to bind serum albumin, extending its half-life from minutes to roughly one week. Approval for chronic weight management followed in 2021, based on large cardiovascular and obesity outcome trials.
GLP-1 receptors are expressed on pancreatic beta cells, in the gut, and in several brain regions. Receptor activation raises cyclic AMP, enhances glucose-dependent insulin secretion, and suppresses glucagon release when blood glucose is high. Effects on gastric emptying and on hypothalamic appetite circuits reduce energy intake. Because insulin release remains glucose-dependent, the risk of hypoglycemia is low when the drug is used alone. The precise contribution of each pathway to body weight change in humans remains an area of active investigation.
The primary target is the GLP-1 receptor, a class B G protein-coupled receptor expressed on pancreatic beta cells, in the gut, and in several brain regions. Receptor activation raises intracellular cyclic AMP, which potentiates glucose-dependent insulin secretion and lowers glucagon release when blood glucose is elevated. Signalling in the hypothalamus and brainstem is associated with reduced appetite and slower gastric emptying. Because the insulinotropic effect depends on prevailing glucose levels, the hypoglycaemic risk of the peptide alone is described as low in most study settings. The relative contribution of peripheral and central actions remains an active research question.
Large randomised trials in adults with type 2 diabetes and in adults with obesity have reported reductions in body weight and improvements in several cardiovascular risk markers. One outcome trial found a lower incidence of major adverse cardiovascular events in participants with diabetes and established cardiovascular disease. Gastrointestinal effects such as nausea and vomiting are the most frequently reported adverse events and often diminish over time. Changes in lean body mass during weight loss are an area of ongoing investigation. Effects in adolescents and in pregnancy are less well characterised, and current labelling advises against use during pregnancy.
However, it was soon realized that submarines could approach enemy coastlines undetected and decrease the warning time (the time between detection of the missile launch and the impact of the missile) from as much as half an hour to possibly under three minutes. This effect was especially significant to the United States, Britain and China, whose capitals of Washington D.C., London, and Beijing all lay within 100 miles (160 km) of their coasts. Moscow was much more secure from this type of threat, due to its considerable distance from the sea. This greatly increased the credibility of a "surprise first strike" by one faction and (theoretically) made it possible to knock out or disrupt the chain of command of a target nation before any counterstrike could be ordered (known as a "decapitation strike"). It strengthened the notion that a nuclear war could possibly be "won", resulting not only in greatly increased tensions and increasing calls for fail-deadly control systems, but also in a dramatic increase in military spending. The submarines and their missile systems were very expensive, and one fully equipped nuclear-powered and nuclear-armed missile submarine could cost more than the entire GNP of a developing country. It was also calculated, however, that the greatest cost came in the development of both sea- and land-based anti-submarine defenses and in improving and strengthening the "chain of command", and as a result, military spending skyrocketed. South Africa developed a nuclear weapon capability during the 1970s and early 1980s.
== Treatment == Treatment is dependent on the type of glycogen storage disease. Von Gierke disease (GSD-I) is typically treated with frequent small meals of carbohydrates and cornstarch, called modified cornstarch therapy, to prevent low blood sugar, while other treatments may include allopurinol and human granulocyte colony stimulating factor. Cori/Forbes disease (GSD-III) treatment may use modified cornstarch therapy, a high protein diet with a preference to complex carbohydrates. However, unlike GSD-I, gluconeogenesis is functional, so simple sugars (sucrose, fructose, and lactose) are not prohibited. A ketogenic diet has demonstrated beneficial for McArdle disease (GSD-V) as ketones readily convert to acetyl CoA for oxidative phosphorylation, whereas free fatty acids take a few minutes to convert into acetyl CoA. For phosphoglucomutase deficiency (formerly GSD-XIV), D-galactose supplements and exercise training has shown favourable improvement of signs and symptoms. In terms of exercise training, some patients with phosphoglucomutase deficiency also experience "second wind." For McArdle disease (GSD-V), regular aerobic exercise utilizing "second wind" to enable the muscles to become aerobically conditioned, as well as anaerobic exercise (strength training) that follows the activity adaptations so as not to cause muscle injury, helps to improve exercise intolerance symptoms and maintain overall health.
Beginning in the 1970s, research was initiated to address sources of indoor radon, determinants of concentration, health effects, and mitigation approaches. In the US, the problem of indoor radon received widespread publicity and intensified investigation after a widely publicized incident in 1984. During routine monitoring at a Pennsylvania nuclear power plant, a worker was found to be contaminated with radioactivity. A high concentration of radon in his home was subsequently identified as responsible.
== Medical uses == Relugolix is approved in the United States, Canada and the United Kingdom for the treatment of prostate cancer, in Japan for the treatment of uterine fibroids (uterine leiomyoma) and in the United Kingdom for endometriosis.
Sources: en.wikipedia.org
Throughout recorded history, attempts at producing a state of general anesthesia can be traced back to the writings of ancient Sumerians, Babylonians, Assyrians, Akkadians, Egyptians, Persians, Indians, and Chinese. Despite significant advances in anatomy and surgical techniques during the Renaissance, surgery remained a last-resort treatment largely due to the pain associated with it. This limited surgical procedures to addressing only life-threatening conditions, with techniques focused on speed to limit blood loss. All of these interventions carried high risk of complications, especially death. Around 80% of surgeries led to severe infections, and 50% of patients died either during surgery or from complications thereafter. Many of the patients who were fortunate enough to survive remained psychologically traumatized for the rest of their lives. However, scientific discoveries in the late 18th and early 19th centuries paved the way for the development of modern anesthetic techniques. The 19th century was filled with scientific advancements in pharmacology and physiology. During the 1840s, the introduction of diethyl ether (1842), nitrous oxide (1844), and chloroform (1847) as general anesthetics revolutionized modern medicine. The late 19th century also saw major advancements to modern surgery with the development and application of antiseptic techniques as a result of the germ theory of disease, which significantly reduced morbidity and mortality rates.
Normally folded proteins have to unfold partially before aggregation can take place through one of these mechanisms. In some cases, however, folded proteins can aggregate without crossing the major energy barrier for unfolding, by populating native-like conformations as a consequence of thermal fluctuations, ligand release or local unfolding occurring in particular circumstances. In these native-like conformations, segments that are normally buried or structured in the fully folded and possessing a high propensity to aggregate become exposed to the solvent or flexible, allowing the formation of native-like aggregates, which convert subsequently into nuclei and fibrils. This process is called 'native-like aggregation' (green arrows in the figure) and is similar to the 'nucleated conformational conversion' model. A later model of amyloid fibril formation involves the intervention of secondary events, such as 'fragmentation', in which a fibril breaks into two or more shorter fibrils, and 'secondary nucleation', in which fibril surfaces (not fibril ends) catalyze the formation of new nuclei. Both secondary events increase the number of fibril ends able to recruit new monomers or oligomers, therefore accelerating fibril formation through a positive feedback mechanism. These events add to the well recognised steps of primary nucleation (formation of the nucleus from the monomers through one of models described above), fibril elongation (addition of monomers or oligomers to growing fibril ends) and dissociation (opposite process).
leukocytes with specific granules), which include the neutrophils, innate lymphoid cells, mast cells, eosinophils, and basophils. Innate lymphoid cells (ILCs) derived from common lymphoid progenitor and belong to the lymphoid lineage. Mast cells reside in connective tissues and mucous membranes and regulate the inflammatory response. They are most often associated with allergy and anaphylaxis. Basophils and eosinophils are related to neutrophils. They secrete chemical mediators that are involved in defending against parasites and play a role in allergic reactions, such as asthma. Natural killer cells (NK cells) do not directly attack invading microbes but destroy compromised host cells, such as tumor cells or virus-infected cells. NK cells recognise such cells by a condition known as "missing self", which involves low levels of a cell-surface marker called MHC I (major histocompatibility complex)—a situation that can arise in viral infection. Normal body cells are not recognized and attacked by NK cells because they express intact self MHC antigens, which inhibit NK cell activity. Monocytes, upon moving to injured tissue, turn into dendritic cells and macrophages while promoting tissue healing. The major humoral component of the innate immune response is the complement system, a biochemical cascade that attacks the surfaces of foreign cells.
=== Dissolved gases === Oxygen dissolved in water can lead to unwanted oxidation of silicon wafers and other materials while gases like carbon dioxide lead to unwanted acidification of water and must be removed. Gases can be removed through various methods including thermal or pressure degassing, membrane degassers or chemical degassing.
=== Material properties === The molecular weight of this rare amino acid that is found in elastin is 526.611 g/mol. The desmosine pyridinium ring has three allysyl side chains and one unaltered lysyl side chain. It has been tested to show that the pyridinium core of Desmosine remains intact even at very high collision energies.
Sources: en.wikipedia.org
Native GLP-1 is degraded within minutes by circulating enzymes. The synthetic version carries substitutions at positions that block enzymatic cleavage, plus a fatty acid side chain that promotes albumin binding. These two changes together extend circulation time from minutes to roughly a week.
Albumin binding keeps a large fraction of the compound in a slowly released reservoir within the bloodstream. Plasma levels decline gradually rather than falling sharply after each administration. That profile supports dosing intervals measured in days instead of hours.
The active peptide sequence is the same in both formats. The oral version adds an absorption enhancer that is not present in the injected solution. Differences in excipients and formulation affect uptake rather than the identity of the active molecule.
Native GLP-1 is a short-lived peptide cleared within one to two minutes by dipeptidyl peptidase-4 and related enzymes. Semaglutide keeps the receptor-binding backbone but adds substitutions and a lipid chain. These changes block the main cleavage site and allow reversible albumin binding, extending the half-life to roughly 165 hours.