Reverse-phase HPLC raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-03-12 and is reviewed periodically as new material appears.
Activation of the GLP-1 receptor couples to Gs signalling and raises intracellular cyclic AMP in pancreatic beta cells. The resulting insulin release depends on prevailing glucose concentrations, so the effect is greater when glucose is elevated. Receptor engagement also suppresses glucagon secretion and slows gastric emptying, which flattens post-meal glucose excursions. In the central nervous system, signalling in hypothalamic and brainstem regions is associated with reduced appetite and lower energy intake. Studies continue to examine effects on cardiac, renal and hepatic endpoints; whether those benefits are independent of weight change remains an open question.
Clinical development of this compound followed earlier short-acting GLP-1 analogues that required frequent injection. Once-weekly subcutaneous formulations entered use after 2017, and an oral formulation using a permeation enhancer later became available. The oral version pairs the peptide with sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, a carrier that improves uptake across the gastric epithelium. Interest has expanded from glycaemic control into weight management and metabolic liver disease. Regulatory status and approved indications differ between countries, and the product remains subject to ongoing safety monitoring.
该分子作为 GLP-1 受体的选择性激动剂发挥作用，受体属于 B 类 G 蛋白偶联受体家族，激活后经 Gs 通路提升细胞内环腺苷酸水平。在胰腺 β 细胞，信号促进葡萄糖依赖性的胰岛素释放，血糖偏低时该作用明显减弱。在胰岛 α 细胞，胰高血糖素分泌受到抑制。中枢神经系统与胃肠道同样存在受体表达，相应信号参与食欲调节以及胃排空速率的降低。
皮下注射后吸收相对缓慢，绝对生物利用度约为百分之八十九，血药浓度峰值通常出现在给药后一到三天。与白蛋白结合使清除减慢，终末半衰期约为一百六十五小时，接近一周。连续给药约四到五周后达到稳态暴露水平。表观分布容积约为每千克零点二五升，血浆蛋白结合率超过百分之九十九。代谢以蛋白水解切割和脂肪二酸侧链的 β-氧化为主，相关产物主要经尿液与粪便排出。
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C187H291N45O59 | Parent peptide; salt forms also reported |
| Molecular mass | about 4113.6 Da | Average mass of the free peptide |
| Peptide length | 31 amino acids | Backbone related to GLP-1(7-37) |
| Key substitution | Aib at position 8 | Blocks DPP-4 cleavage |
| Albumin binding | Via C-18 diacid side chain | Prolongs circulation time |
Semaglutide dissolves readily in water and in aqueous buffers near neutral pH. Solubility decreases near the isoelectric point, where net charge is minimal. Common laboratory solvents include phosphate-buffered saline and dilute ammonium bicarbonate. Strongly acidic or basic conditions may accelerate hydrolysis. Working concentrations are usually prepared by diluting a concentrated stock. Vial surfaces can adsorb small amounts of peptide at low concentrations, so carrier proteins or low-binding tubes are sometimes used.
Reverse-phase high-performance liquid chromatography is the standard method for purity assessment, separating the peptide from truncated or oxidized variants. Mass spectrometry confirms molecular mass and detects modifications, while ultraviolet absorbance near 280 nanometers supports concentration measurement through tryptophan and tyrosine residues. Circular dichroism can indicate secondary structure, though the peptide is largely helical in solution, and ion-exchange chromatography resolves charge variants. Purity values above 95 percent are typical for research-grade material. Stability studies track degradation over time under defined conditions.
Lyophilized semaglutide is typically stored at temperatures between minus 20 and minus 80 degrees Celsius for long-term preservation. Short-term storage at 2 to 8 degrees Celsius is common for working aliquots. Repeated freeze-thaw cycles can degrade the peptide and are usually avoided. The molecule is hygroscopic in its solid form, so containers should remain sealed with desiccant. Solutions are less stable than powders and are generally prepared fresh. Light exposure is limited because aromatic residues can undergo photo-oxidation.
Stability studies examine how temperature, pH, and moisture influence degradation rates over time. In aqueous solution, hydrolysis and deamidation accelerate as pH moves away from mildly acidic conditions. Light exposure and residual metal ions can also trigger oxidation of susceptible residues. Accelerated aging at elevated temperature is used to estimate shelf life, though extrapolation to room temperature carries uncertainty because individual degradation pathways do not always scale predictably.
Lyophilized semaglutide powder is typically held at minus twenty degrees Celsius for long-term storage. At that temperature, solid-state degradation reactions proceed slowly and the peptide remains intact for extended periods. Repeated freeze-thaw cycles are best avoided because they promote aggregation and can shift the proportion of monomeric peptide present. Working aliquots are often prepared so that each portion is thawed only once, and desiccant is placed inside the vial to limit moisture uptake.
Identity and purity are usually assessed by reverse-phase high-performance liquid chromatography coupled to mass spectrometry. Retention time and observed mass are compared against a reference standard run under identical conditions. Impurity profiles reveal deamidation products, oxidized methionine variants, and truncated fragments that arise during synthesis or storage. Peptide mapping through enzymatic digestion confirms the primary sequence, while amino acid analysis offers an independent check on overall composition.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 or 280 nanometres is widely used to assess purity and to resolve related impurities. Liquid chromatography coupled to mass spectrometry confirms identity through the protonated molecular ion and fragment ions formed in tandem experiments. Capillary electrophoresis and peptide mapping after enzymatic digestion supply complementary information on charge variants and modification sites. Circular dichroism and nuclear magnetic resonance can report on secondary structure in solution. Absolute quantification usually depends on an external standard, and reported purity depends on the detection wavelength and integration parameters chosen.
Lyophilised material appears as a white to off-white cake or powder that is hygroscopic, and containers are usually equilibrated to room temperature before opening to limit condensation. Dissolution is performed in water, phosphate-buffered saline, or a mildly alkaline buffer, since solubility rises above neutral pH. Gentle inversion or low-speed mixing is preferred, because vigorous vortexing can promote surface denaturation and aggregation. Complete dissolution may require several minutes, and brief sonication is sometimes applied. Passing the solution through a 0.22 micrometre membrane removes particulates but does not by itself sterilise the liquid.
Around the end of the 16th century, increasing Cossack aggression strained relations between the Commonwealth and the Ottoman Empire. Cossacks had begun raiding Ottoman territories during the second part of the 16th century. The Polish government could not control them, but was held responsible as the men were nominally its subjects. In retaliation, Tatars living under Ottoman rule launched raids into the Commonwealth, mostly in the southeast territories. Cossack pirates responded by raiding wealthy trading port-cities in the heart of the Ottoman Empire, as these were just two days away by boat from the mouth of the Dnieper river. In 1615 and 1625, Cossacks razed suburbs of Constantinople, forcing the Ottoman Sultan to flee his palace. In 1637, the Zaporozhian Cossacks, joined by the Don Cossacks, captured the strategic Ottoman fortress of Azov, which guarded the Don. The Zaporizhian Cossacks became particularly strong in the first quarter of the 17th century under the leadership of hetman Petro Konashevych-Sahaidachny, who launched successful campaigns against the Tatars and Turks. Tsar Boris Godunov had incurred the hatred of Ukrainian Cossacks by ordering the Don Cossacks to drive away from the Don all the Ukrainian Cossacks fleeing the failed uprisings of the 1590s. This contributed to the Ukrainian Cossacks' willingness to fight against him. In 1604, 2,000 Zaporizhian Cossacks fought on the side of the Polish-Lithuanian Commonwealth and their proposal for the Tsar (Dmitri I), against the Muscovite army.
=== Genetics === An association between biliary atresia and the ADD3 gene was first detected in Chinese populations through a genome-wide association study, and was confirmed in Thai Asians and Caucasians. A possible association with deletion of the gene GPC1, which encodes a glypican 1-a heparan sulfate proteoglycan, has been reported. This gene is located on the long arm of chromosome 2 (2q37) and is involved in the regulation of inflammation and the Hedgehog gene. Egyptian infants with biliary atresia were found to have null GSTM1 genotype while all their mothers were heterozygous for GSTM1. Thus these infants may be protected in utero by their maternal detoxification system, yet once born they cannot handle the detoxification of an aflatoxin load.
=== Protein cleavage === Cyanogen bromide hydrolyzes peptide bonds at the C-terminus of methionine residues. This reaction is used to reduce the size of polypeptide segments for identification and sequencing.
Sources: en.wikipedia.org
== External links == "Tyrian Purple". World History Encyclopedia. Cooksey CJ (1994). "Making Tyrian purple". Dyes in History and Archaeology. 13: 7–13 (email the author for a copy). Archived from the original on 2020-07-26. Retrieved 2010-05-11. Source of article in author's Bibliography page. Guckelsberger M (December 2013). Purple Murex Dye in Antiquity (PDF) (Thesis). University of Iceland. "Tyrian purple". The Free Library. "Royal Purple of Tyre" (PDF).
The protein is an enzyme that normally degrades the alpha -1,4 and alpha -1,6 linkages in glycogen, maltose and isomaltose and is required for the degradation of 1–3% of cellular glycogen. The deficiency of this enzyme results in the accumulation of structurally normal glycogen in lysosomes and cytoplasm in affected individuals. Excessive glycogen storage within lysosomes may interrupt the normal functioning of other organelles and lead to cellular injury. A putative homologue—acid alpha-glucosidase-related gene 1—has been identified in the nematode Caenorhabditis elegans.
=== Iranian plan === Cessation of the war on Iraq, Lebanon, and Yemen Cessation of the war in Iran with no time limit Ending all conflicts in the region Reopening the Strait of Hormuz Establishing a protocol and conditions to ensure freedom and security of navigation in the Strait Full payment of war reparations to Iran Lifting sanctions on Iran Release of the Iranian frozen assets held by the United States Iran commits to not seeking possession of any nuclear weapons Immediate ceasefire on all fronts upon the ceasefire announcement Further complicating matters, Iran released several different version of the plan, with small differences, and differences between the Persian and English versions.
=== Types === The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A, B, AB, and O) in 1907, which remains in use today. In 1907 the first blood transfusion was performed that used the ABO system to predict compatibility. The first non-direct transfusion was performed on 27 March 1914. The Rhesus factor was discovered in 1937.
Sources: en.wikipedia.org
Some paleolithic hunter-gatherers consumed a significant amount of meat and possibly obtained most of their food from hunting, while others were believed to have a primarily plant-based diet. Most, if not all, are believed to have been opportunistic omnivores. One hypothesis is that carbohydrate tubers (plant underground storage organs) may have been eaten in high amounts by pre-agricultural humans. It is thought that the Paleolithic diet included as much as 1.65–1.9 kg (3.6–4.2 lb) per day of fruit and vegetables. The relative proportions of plant and animal foods in the diets of Paleolithic people often varied between regions, with more meat being necessary in colder regions (which were not populated by anatomically modern humans until c. 30,000 – c. 50,000 BP). It is generally agreed that many modern hunting and fishing tools, such as fish hooks, nets, bows, and poisons, were not introduced until the Upper Paleolithic and possibly even Neolithic. The only hunting tools widely available to humans during any significant part of the Paleolithic were hand-held spears and harpoons. There is evidence of Paleolithic people killing and eating seals and elands as far as c. 100,000 BP. On the other hand, buffalo bones found in African caves from the same period are typically of very young or very old individuals, and there is no evidence that pigs, elephants, or rhinos were hunted by humans at the time. Paleolithic peoples suffered less famine and malnutrition than the Neolithic farming tribes that followed them.
Biko opposed any collaboration with the apartheid government, such as the agreements that the Coloured and Indian communities made with the regime. In his view, the Bantustan system was "the greatest single fraud ever invented by white politicians", stating that it was designed to divide the Bantu-speaking African population along tribal lines. He openly criticised the Zulu leader Mangosuthu Buthelezi, stating that the latter's co-operation with the South African government "[diluted] the cause" of black liberation. He believed that those fighting apartheid in South Africa should link with anti-colonial struggles elsewhere in the world and with activists in the global African diaspora combating racial prejudice and discrimination. He also hoped that foreign countries would boycott South Africa's economy. Biko believed that while apartheid and white-minority rule continued, "sporadic outbursts" of violence against the white minority were inevitable. He wanted to avoid violence, stating that "if at all possible, we want the revolution to be peaceful and reconciliatory". He noted that views on violence differed widely within the BCM – which contained both pacifists and believers in violent revolution – although the group had agreed to operate peacefully, and unlike the PAC and ANC, had no armed wing. A staunch anti-imperialist, Biko saw the South African situation as a "microcosm" of the broader "black–white power struggle" which manifests as "the global confrontation between the Third World and the rich white nations of the world".
The signs and symptoms of ankylosing spondylitis often appear gradually, with peak onset between 20 and 30 years of age. Initial symptoms are usually a chronic dull pain in the lower back or gluteal region combined with stiffness of the lower back. Individuals often experience pain and stiffness that awakens them in the early morning hours. As the disease progresses, loss of spinal mobility and chest expansion, with a limitation of anterior flexion, lateral flexion, and extension of the lumbar spine are seen. Systemic features are common with weight loss, fever, or fatigue often present. Pain is often severe at rest but may improve with physical activity. Inflammation and pain may recur to varying degrees regardless of rest and movement. AS can occur in any part of the spine or the entire spine, often with pain localized to either buttock or the back of the thigh from the sacroiliac joint. Arthritis in the hips and shoulders may also occur. When the condition presents before the age of 18, AS is more likely to cause pain and swelling of large lower limb joints, such as the knees. In prepubescent cases, pain and swelling may also manifest in the ankles and feet, where heel pain and enthesopathy commonly develop. Less common occurrences include ectasia of the sacral nerve root sheaths. About 30% of people with AS will also experience anterior uveitis, causing eye pain, redness, and blurred vision. This is thought to be due to the association that both AS and uveitis have with the presence of the HLA-B27 antigen.
In February 2007, a 2003 sex tape made by sister Kim Kardashian and her former boyfriend Ray J, Kim Kardashian, Superstar, was leaked, which contributed to the family's rise in popularity. Later that year, Khloé; her mother Kris; her stepparent Caitlyn; her siblings Kourtney, Kim, and Rob; and half-sisters Kendall and Kylie were commissioned to star in the reality television series Keeping Up with the Kardashians. The series and her sister Kim's popularity led to the Kardashians being able to cash in by endorsing products. These include waist-slimming pants, beauty products and Coca-Cola, for which they are paid (as of 2016) $75,000 per post on Instagram, Facebook and Twitter. The series proved successful for E!, the network on which it is broadcast, and has led to the creations of spin-offs including Kourtney and Khloé Take Miami and Khloé & Lamar.
=== Pacific islands === During an El Niño event, New Zealand tends to experience stronger or more frequent westerly winds during their summer, which leads to an elevated risk of drier than normal conditions along the east coast. There is more rain than usual though on New Zealand's West Coast, because of the barrier effect of the North Island mountain ranges and the Southern Alps. Fiji generally experiences drier than normal conditions during an El Niño, which can lead to drought becoming established over the Islands. However, the main impacts on the island nation is felt about a year after the event becomes established. Within the Samoan Islands, below average rainfall and higher than normal temperatures are recorded during El Niño events, which can lead to droughts and forest fires on the islands. Other impacts include a decrease in the sea level, possibility of coral bleaching in the marine environment and an increased risk of a tropical cyclone affecting Samoa. In the late winter and spring during El Niño events, drier than average conditions can be expected in Hawaii. On Guam during El Niño years, dry season precipitation averages below normal, but the probability of a tropical cyclone is more than triple what is normal, so extreme short duration rainfall events are possible. On American Samoa during El Niño events, precipitation averages about 10 percent above normal, while La Niña events are associated with precipitation averaging about 10 percent below normal.
Sources: en.wikipedia.org
It belongs to the incretin mimetic class and acts as a long-acting glucagon-like peptide-1 receptor agonist. The class includes several peptides with different half-lives and routes of administration.
The side chain enables reversible binding to albumin in the bloodstream, which protects the peptide from rapid renal clearance. This extends the interval between administrations compared with unmodified GLP-1.
No. It shares much of the native sequence but carries substitutions and an added side chain. These changes increase stability against enzymatic breakdown.
差别集中在三处：第 8 位残基被非天然氨基酸取代，第 34 位换成精氨酸，第 26 位增加一条脂肪酸侧链。前两处改动降低酶解速率，侧链则通过白蛋白结合延长循环时间。综合结果是半衰期从约两分钟延长到约一周。