deamidation raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2025-09-15. 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。
Reversed-phase high-performance liquid chromatography with ultraviolet detection is the dominant approach for peptide purity assessment, usually paired with mass spectrometry to confirm molecular mass and sequence. Peptide mapping by enzymatic digestion and tandem mass spectrometry locates modifications such as deamidation and oxidation. Quantitation in plasma matrices can be performed by LC-MS/MS after solid-phase extraction. Method validation follows general guidance on accuracy, precision, linearity, and limits of detection. Comparability of results between laboratories, when no shared reference standard is available, remains an open question.
Stability studies focus on deamidation of asparagine and glutamine residues, oxidation of methionine, and aggregation into higher-order species. The fatty acid side chain adds susceptibility to oxidative change and can promote self-association at high concentration. Lyophilised material is comparatively robust when kept cold and dry, while aqueous solutions require refrigeration and protection from light. Forced degradation experiments under heat, acid, base, and peroxide conditions establish the specificity of each analytical method. Which degradation route dominates under real storage conditions depends on the formulation and stays formulation-specific.
| 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 |
=== Artifacts === Artifacts are structures or features in tissue that interfere with normal histological examination. Artifacts interfere with histology by changing the tissues appearance and hiding structures. Tissue processing artifacts can include pigments formed by fixatives, shrinkage, washing out of cellular components, color changes in different tissues types and alterations of the structures in the tissue. An example is mercury pigment left behind after using Zenker's fixative to fix a section. Formalin fixation can also leave a brown to black pigment under acidic conditions.
EsF3 + 3 Li → Es + 3 LiF However, owing to its low melting point and high rate of self-radiation damage, einsteinium has a higher vapor pressure than lithium fluoride. This makes this reduction reaction rather inefficient. It was tried in the early preparation attempts and quickly abandoned in favor of reduction of einsteinium(III) oxide with lanthanum metal:
== Peptide removal == Peptides that fail to bind MHC class I molecules in the lumen of the endoplasmic reticulum (ER) are removed from the ER via the sec61 channel into the cytosol, where they might undergo further trimming in size, and might be translocated by TAP back into ER for binding to a MHC class I molecule. For example, an interaction of sec61 with bovine albumin has been observed.
Sources: en.wikipedia.org
==== Food industry ==== The PEG–NaCl system has been shown to be effective at partitioning small molecules, such as peptides and nucleic acids. These compounds are often flavorants or odorants. The system could then be used by the food industry to isolate or eliminate particular flavors. Caffeine extraction used to be done using liquid–liquid extraction, specifically direct and indirect liquid–liquid extraction (Swiss Water Method), but has since moved towards super-critical CO2 as it is cheaper and can be done on a commercial scale.
In bacteria and organelles, the initiation of protein synthesis is signaled by the formation of formyl-methionyl-tRNA (tRNAfMet). This reaction is dependent on 10-formyltetrahydrofolate, and the enzyme methionyl-tRNA formyltransferase. This reaction is not used by eukaryotes or Archaea, as the presence of tRNAfMet in non bacterial cells is dubbed as intrusive material and quickly eliminated. After its production, tRNAfMet is delivered to the 30S subunit of the ribosome in order to start protein synthesis. fMet possesses the same codon sequence as methionine. However, fMet is only used for the initiation of protein synthesis and is thus found only at the N terminus of the protein. Methionine is used during the rest translation. In E. coli, tRNAfMet is specifically recognized by initiation factor IF-2, as the formyl group blocks peptide bond formation at the N-terminus of methionine. Once protein synthesis is accomplished, the formyl group on methionine can be removed by peptide deformylase. The methionine residue can be further removed by the enzyme methionine aminopeptidase.
==== Public transit ==== The city government relaxed regulations on the use of masks on city buses, a decision contested by specialists who stated that the policy would enable the spread of COVID-19. The other measures to loosen anti-pandemic protocols were criticized by health researchers for bringing risks to public health. Ahead of the acceleration of the number of people infected, the municipal government had to return to prohibiting passengers standing on public transit on 25 February, two days before the policy was set to begin. Meanwhile, the government was not able to adapt to the restriction, and users of public transit reported waiting more than an hour and a half at stops. The city government argued that there would be more than 400 professionals taken out of work because they had contracted COVID-19 or had a family member with the virus.
==== Enzymes used ==== A commonly used protease mixture is "Flavourzyme", extracted from Aspergillus oryzae, the mold used for soy sauce production. This mixture contains both endo- and exo-peptidases. The endopeptidase Alcalase may also be used, but without an exopeptidase it tends to generate a bitter flavor. As a result, it should be used with a companion exopeptidase. A commercial exopeptidase produced for this purpose is "Protana Prime", a mixture with both leucine aminopeptidase and carboxypeptidase D activity. Beyond proteolysis, the amount of umami taste can also be increased by adding a glutaminase, which converts glutamine to glutamate. Commercial options include "Protana Boost" and others.
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。
Purity is commonly expressed as the percentage of the main peak relative to all integrated peaks in a reversed-phase chromatogram. Related substances and counter-ions are reported separately. Values obtained with different detectors are not always directly comparable.