The short version of 二肽基肽酶-4 fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-06-21. Anything still debated is marked as such rather than presented as settled.
序列层面的改动同时解决了两个问题，即酶解稳定性与肾脏清除速度。天然 GLP-1 在循环中的半衰期仅约两分钟，主要被二肽基肽酶-4 迅速灭活。酰化侧链与白蛋白的可逆结合形成循环储库，使分子缓慢释放并持续激活受体。这种设计思路后来被广泛用于同类长效肽的开发，属于该类药物化学改造的典型范式。
Semaglutide 是一种经结构修饰的胰高血糖素样肽-1 类似物，其主链与内源性 GLP-1(7-36) 约有百分之九十四的序列一致性。第 8 位丙氨酸被 α-氨基异丁酸取代，使二肽基肽酶-4 无法识别原有切割位点。第 34 位赖氨酸换为精氨酸，进一步降低酶解速率。第 26 位赖氨酸经间隔基连接一条含十八个碳的二酸脂肪链，该侧链赋予分子与血浆白蛋白结合的能力。
Quality control for research material typically involves reversed-phase HPLC for purity and identity, mass spectrometry for molecular weight confirmation, and Karl Fischer titration for residual water content. Peptide content is often reported as the mass of actual peptide rather than total powder mass, since counterions and water contribute to the latter. A certificate of analysis should list the method used for each specification. Limits and acceptance criteria vary by supplier and by intended application.
Handling practices center on minimizing contamination and adsorption. Lyophilized peptide tends to accumulate static charge, so weighing is done with antistatic measures and calibrated balances. Reconstitution with appropriate solvent should be gentle, avoiding vigorous vortexing that generates foam and shear. Solutions are typically aliquoted before freezing to reduce repeated temperature cycling. Personal protective equipment and a fume hood are standard for powder handling.
| Property | Value | Notes |
|---|---|---|
| 分子式 | C187H291N45O59 | 按主链与 C18 二酸侧链计算 |
| 分子量 | 约 4113.6 道尔顿 | 游离碱形式，随反离子略有差异 |
| 外观 | 白色至类白色冻干粉末 | 具吸湿性，需干燥保存 |
| 溶解性 | 微溶于水，易溶于碱性缓冲液 | 溶解性随 pH 升高而改善 |
| 等电点 | 约 5.4 | 影响缓冲液选择与聚集倾向 |
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.
Semaglutide is a synthetic peptide analogue of glucagon-like peptide-1, a gut hormone released by intestinal L cells after food intake. The natural hormone acts on pancreatic and central receptors but is degraded within minutes by dipeptidyl peptidase-4 and other peptidases. Semaglutide belongs to the class of long-acting GLP-1 receptor agonists, a group distinguished by structural changes that slow breakdown and extend circulation time. Its development followed earlier short-acting analogues and reflects a general strategy in peptide drug design: preserve receptor activity while blocking proteolytic clearance.
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.
纯度评价多采用反相高效液相色谱，流动相常加入三氟乙酸或甲酸作为离子对改性剂，检测波长设在二百一十四纳米或二百二十纳米。分子量确认依靠电喷雾电离质谱或基质辅助激光解吸电离质谱，实测值应与理论值在数 ppm 内吻合。肽图分析通过酶切后液相色谱串联质谱完成，用于核查序列与修饰位点。体积排阻色谱用于定量共价与非共价聚集体。生物基质浓度测定则采用免疫分析或液相色谱串联质谱。
肽类的主要降解路径包括天冬酰胺脱酰胺、甲硫氨酸氧化、天冬氨酸异构化以及由 β-折叠驱动的聚集，这些反应对 pH 与缓冲液种类较为敏感。磷酸盐、丙二醇与苯酚等辅料会影响局部微环境与界面行为。强制降解研究借助高温、强光、氧化剂与极端 pH 暴露来预测产物谱。关于长期室温存放的数据相对有限，超出标签条件的稳定性仍属开放问题，需要在具体制剂中通过实时与加速试验加以确认。
容器与密封系统同样参与稳定性表现。硅油涂层、胶塞材质与顶空氧含量可能改变聚集速率与氧化水平。分析结果因此需要在完整包装形式下评估，而不能仅凭原料药数据推断。法规文件通常要求同时提交批次数据与代表性容器中的稳定性趋势。
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.
Storage at minus 20 degrees Celsius or lower in a desiccated container preserves the peptide for extended periods, while working solutions are commonly held at two to eight degrees Celsius for short intervals. Light exposure and repeated freeze-thaw cycles accelerate degradation, so dividing material into single-use aliquots is generally recommended. Adsorption to glass and plastic surfaces can lower the measured concentration of dilute solutions, particularly below one milligram per millilitre. The degradation routes most often reported for GLP-1 analogues are deamidation, methionine oxidation, and backbone hydrolysis. Relative rates under specific conditions are frequently described only for individual formulations.
Quantification and purity assessment rely on separation methods coupled to optical or mass detection. Reversed-phase high-performance liquid chromatography resolves the intact peptide from related impurities and is the standard assay technique. Size-exclusion chromatography measures aggregates, while ion-exchange chromatography separates charge variants produced by deamidation. Mass spectrometry confirms identity and detects mass shifts of a few daltons. In biological matrices, liquid chromatography with tandem mass spectrometry is often used because immunoassays can cross-react with endogenous GLP-1 or with circulating fragments.
As a peptide, semaglutide is sensitive to conditions that break amide bonds or modify side chains. Deamidation of asparagine and glutamine residues, oxidation of methionine and tryptophan, and non-covalent aggregation are the main degradation routes described in published stability work. Rate depends strongly on pH, buffer species, ionic strength, temperature and exposure to light. Formulators therefore choose a defined solution pH and often add excipients such as phosphate buffer, propylene glycol and phenol, each of which plays a separate role in pH control, tonicity or preservation.
Storage guidance for the finished injectable product distinguishes the unused state from the in-use state. Before first use, pens are kept refrigerated between 2 and 8 degrees Celsius, protected from light, and never frozen, since freezing can disrupt the peptide or the device. After first use, label instructions in several markets permit storage at room temperature up to about 30 degrees Celsius for a limited number of days. Solid research-grade material is normally held at or below minus 20 degrees Celsius, often with desiccant, and allowed to equilibrate before opening.
== Structure == Fibronectin exists as a protein dimer, consisting of two nearly identical polypeptide chains linked by a pair of C-terminal disulfide bonds. Each fibronectin subunit has a molecular weight of approximately 230–275 kDa and contains multiple copies of three types of modules: type I, II, and III. All three modules are composed of two anti-parallel β-sheets resulting in a beta-sandwich; however, type I and type II are stabilized by intra-chain disulfide bonds, while type III modules do not contain any disulfide bonds. The absence of disulfide bonds in type III modules allows them to partially unfold under applied force. Three regions of variable splicing occur along the length of the fibronectin protomer. One or both of the "extra" type III modules (EIIIA and EIIIB) may be present in cellular fibronectin, but they are never present in plasma fibronectin. A "variable" V-region exists between III14–15 (the 14th and 15th type III module). The V-region structure is different from the type I, II, and III modules, and its presence and length may vary. The V-region contains the binding site for α4β1 integrins. It is present in most cellular fibronectin, but only one of the two subunits in a plasma fibronectin dimer contains a V-region sequence. The modules are arranged into several functional and protein-binding domains along the length of a fibronectin monomer. There are four fibronectin-binding domains, allowing fibronectin to associate with other fibronectin molecules.
In addition, the bioavailability of (E)-doxepin was about 2-fold lower in extensive relative to poor CYP2D6 metabolizers, indicating a significant role of CYP2D6 in the first-pass metabolism of (E)-doxepin. The clearance of (E)-doxepin in CYP2C9 slow metabolizers was also significantly reduced at 238 L/hour. CYP2C19 was involved in the metabolism of (Z)-doxepin, with clearance rates of 191 L/hour in CYP2C19 extensive metabolizers and 73 L/hour in poor metabolizers (~2.5-fold difference). Area-under-the-curve (0–48 hour) levels of nordoxepin were dependent on the genotype of CYP2D6 with median values of 1.28, 1.35, and 5.28 nM•L/hour in CYP2D6 extensive, intermediate, and poor metabolizers, respectively (~4-fold difference between extensive and poor). Taken together, doxepin metabolism appears to be highly stereoselective, and CYP2D6 genotype has a major influence on the pharmacokinetics of (E)-doxepin. Moreover, CYP2D6 poor metabolizers, as well as patients taking potent CYP2D6 inhibitors (which can potentially convert a CYP2D6 extensive metabolizer into a poor metabolizer), may be at an increased risk for adverse effects of doxepin due to their slower clearance of the drug. Another study assessed doxepin and nordoxepin metabolism in CYP2D6 ultra-rapid, extensive, and poor metabolizers following a single 75 mg oral dose. They found up to more than 10-fold variation in total exposure to doxepin and nordoxepin between the different groups.
== History == In a multi-center, randomized trial in participants with active Graves' ophthalmopathy, teprotumumab was more effective than placebo. In February 2019, Horizon announced results from a Phase III confirmatory trial evaluating teprotumumab for the treatment of active thyroid eye disease (TED). The study met its primary endpoint, showing more participants treated with teprotumumab compared with placebo had a meaningful improvement in proptosis, or bulging of the eye: 82.9% of teprotumumab participants compared to 9.5% of placebo participants achieved the primary endpoint of a 2 mm or more reduction in proptosis (p<0.001). Proptosis is the main cause of morbidity in TED. All secondary endpoints were also met and the safety profile was consistent with the Phase II study of teprotumumab in TED. In July 2019, Horizon submitted a biologics license application to the US Food and Drug Administration (FDA) for teprotumumab for the treatment of active thyroid eye disease. Teprotumumab was first investigated for the treatment of solid and hematologic tumors, including breast cancer, Hodgkin's and non-Hodgkin's lymphoma, non-small cell lung cancer, and sarcoma. Teprotumumab-trbw was approved based on the results of two clinical trials (Trial 1/ NCT01868997 and Trial 2/ NCT03298867) of 170 subjects with active TED who were randomized to either receive teprotumumab-trbw or a placebo.
The violent anti-Peruvian demonstrations in Ecuador and anti-Ecuadorian demonstrations in Peru, the mobilization of forces in both countries, everything made us hope that the armed conflict would break out in 1910, had it not been for the intervention of the United States, Brazil and Argentina. The hostilities between the two do not cease, which leads Ecuador in 1910 to establish a defensive alliance with Colombia, giving it 180,000 km2 of the Amazon area for payment, in exchange for strengthening a possible anti-Peruvian alliance between the two. A gesture that Colombia would betray in the eyes of Ecuador by ceding in 1922 to Peru, the common enemy, half of the territories ceded by it. In the middle of the 20th century, the degree of hostility would have increased to the point of a first armed confrontation in 1941, prompted by a seizure of Peruvian Amazonian territories at the hands of the Ecuadorian army, particularly the rubber zone. During the 2nd Peruvian-Ecuadorian War, the Porotillo Massacre broke out, whereby the Peruvian platoon, commanded by Alfredo Novoa Cava, was massacred in Cune by Ecuadorian troops on September 11, 1941, leaving only one survivor (the captain's nephew); This event, carried out in full truce, filled the Ecuadorian chiefs and officers with pride due to strong anti-Peruvian feelings, but not all the soldiers that made up the Ecuadorian detachment, who felt terrified by the fact that their superiors celebrated as one " victoria" a crime against humanity.
=== Adaptation strategies === Potato production is expected to decline in many areas due to hotter temperatures and decreased water availability. Conversely, production is predicted to become possible in high altitude and latitude areas where it has been limited by frost damage, such as in Canada and Russia. This will shift potato production to cooler areas, mitigating much of the projected decline in yield. However, this may trigger competition for land between potato crops and other land uses, mostly due to changes in water and temperature regimes. The other approach is through the development of varieties or cultivars which would be more adapted to altered conditions. This can be done through 'traditional' plant breeding techniques and genetic modification. These techniques allow for the selection of specific traits as a new cultivar is developed. Certain traits, such as heat stress tolerance, drought tolerance, fast growth/early maturation and disease resistance, may play an important role in creating new cultivars able to maintain yields under stressors induced by climate change. For instance, developing cultivars with greater heat stress tolerance would be critical for maintaining yields in countries with potato production areas near current cultivars' maximum temperature limits (e.g. Sub-Saharan Africa, India). Superior drought resistance can be achieved through improved water use efficiency (amount of food produced per amount of water used) or the ability to recover from short drought periods and still produce acceptable yields.
Sources: en.wikipedia.org
As of March 2006, Tim Hortons commanded 76% of the Canadian market for baked goods (based on the number of customers served) and held 62% of the Canadian coffee market (compared to Starbucks, in the number two position, at 7%). During this period Tim Hortons also introduced the Tim Hortons Express format, a compact kiosk model offering beverages and a limited baked-goods menu. These outlets were installed in non-traditional venues such as universities, airports, and military facilities.
On January 24, 2025, less than a week into Trump's second presidency, he fired 17 independent inspectors general at federal agencies, which appeared to violate federal law that requires advance notice of dismissals to both chambers of congress with reasons given 30 days in advance. Trump also fired all Democratic but not Republican members of the Privacy and Civil Liberties Oversight Board, which would prevent the board from meeting quorum and functioning. Trump also fired members of the Equal Employment Opportunity Commission, National Labor Relations Board and 56 senior officials at USAID for allegedly attempting to thwart his priorities.
The company set up a ghostwriting programme called CASPPER, initially to produce articles about Paxil but which was extended to cover Avandia. As part of the settlement GSK signed a five-year corporate integrity agreement with the Department of Health and Human Services, which obliged the company to make major changes in the way it did business, including changing its compensation programmes for its sales force and executives, and to implement and maintain transparency in its research practices and publication policies. It announced in 2013, that it would no longer pay doctors to promote its drugs or attend medical conferences, and that its sales staff would no longer have prescription targets.
== Bibliography == Szilágyi, Miklós (1988). Electron and ion optics. New York: Plenum Press. ISBN 978-0-306-42717-6. Septier, Albert L. (1980). Applied charged particle optics. Boston: Academic Press. ISBN 978-0-12-014574-4. International vocabulary of basic and general terms in metrology =: Vocabulaire international des termes fondamentaux et généraux de métrologie. International Organization for Standardization. 1993. ISBN 978-92-67-01075-5. IUPAP Red Book SUNAMCO 87-1 "Symbols, Units, Nomenclature and Fundamental Constants in Physics" (does not have an online version) Symbols Units and Nomenclature in Physics IUPAP-25, E.R. Cohen & P. Giacomo, Physics 146A (1987) 1–68
== See also == Hermetic seal – Airtight seal James Webb Space Telescope sunshield – Main cooling system for the infrared observatory Tervis Tumbler – American drinkware manufacturer Thermal cooking – Cooking method Yeti Holdings – American manufacturing company Cooler – Insulated box used to keep food or drink cool
Sources: en.wikipedia.org
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。
胰岛素释放需要细胞内环腺苷酸与钙信号升高，同时依赖葡萄糖代谢产生的协同信号。血糖水平较低时协同信号不足，分泌增强有限。这一机制在降糖效果与低血糖风险之间提供了缓冲。
白蛋白结合是主要原因，它减少肾小球滤过并保护分子免受蛋白酶降解。序列修饰带来的酶解抵抗同样不可忽略，二者共同作用。脂肪链的疏水性还会影响组织分布，但其对总半衰期的贡献程度仍在研究之中。
Sealed, protected from light, and refrigerated at two to eight degrees Celsius for most research material. Desiccated storage limits moisture uptake. Allow the vial to reach room temperature before opening to prevent condensation.