A practical reference on peptide degradation: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-02-06. Anything still debated is marked as such rather than presented as settled.
常规纯度与身份确认依赖反相高效液相色谱，并辅以质谱测定分子量。氨基酸组成分析可用于验证序列构成，肽图分析则能进一步定位修饰或降解产物。杂质谱通常关注缺失序列肽、截短片段和氧化产物。不同方法的检出限并不相同，因此各实验室报告的纯度数值不宜直接横向比较。
多数实验室与市售的 Semax 以冻干粉形式提供。冻干粉通常建议保存在 -20 °C 或更低温度下，同时避免光照与反复升温。短期运输有时采用冷藏条件，但长期保存仍以冷冻为主。分包操作应尽量减少开盖次数，以降低吸湿和微生物污染的风险。开封后若未一次用完，建议在干燥环境中密封并尽快放回低温储存。
The proposed mechanism centres on neurotrophic signalling rather than direct receptor activation. Semax is reported to increase expression of brain-derived neurotrophic factor and nerve growth factor in several brain regions, and to shift the balance between excitatory and inhibitory neurotransmitter systems. Interaction with melanocortin receptors has been suggested because of the parent ACTH fragment. Many of these findings come from rodent studies, and the extent to which they translate to human physiology remains an open question.
Scientific literature on semax is unevenly distributed. A substantial share of published work originates from a small number of laboratories in Russia, while independent replication elsewhere is limited. Human data consist mostly of small trials with short follow-up, and several reported outcomes rely on subjective rating scales. Questions about how much intact peptide reaches the central nervous system after nasal administration, and how long it persists there, are still unresolved. The compound is best described as an active research subject rather than a settled pharmacological agent.
Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. It was derived from the ACTH(4-10) fragment, a short segment of adrenocorticotropic hormone that lacks the hormonal activity associated with the full-length peptide. Researchers at the Institute of Molecular Genetics in Moscow developed the compound during the 1980s. It has been registered as a pharmaceutical product in Russia and several neighbouring countries, where it is supplied as a nasal solution, and it is also sold internationally as a research chemical.
| Property | Value | Notes |
|---|---|---|
| 外观 | 白色至类白色粉末 | 常见于冻干制剂 |
| 溶解度 | 易溶于水 | 在极性溶剂中一般也可溶 |
| 建议储存温度 | -20 °C | 冻干粉，避光密封 |
| 常见分析手段 | 反相高效液相色谱 | 常与质谱联用 |
| 主要降解路径 | 水解与氧化 | 溶液状态更显著 |
Identity and purity of semax are established with reversed-phase high-performance liquid chromatography coupled to ultraviolet detection, usually at 214 nanometres. Mass spectrometry, most often electrospray ionisation in positive mode, confirms the molecular mass and reveals truncated sequences. Amino acid analysis and peptide mapping after enzymatic digestion provide additional structural confirmation. Laboratories typically report purity as the percentage area of the main peak, a figure that does not capture isomeric or oxidised variants unless the method resolves them.
The peptide is prone to several degradation pathways. Oxidation of the methionine residue produces a sulfoxide that elutes close to the parent peak in many chromatographic systems. Hydrolysis of peptide bonds and deamidation of susceptible residues in related sequences also reduce purity over time. Lyophilised material kept dry at minus twenty degrees Celsius and shielded from light is the most stable form commonly described in laboratory practice.
Laboratory descriptions of the material are consistent across suppliers. It appears as a white to off-white lyophilized powder that dissolves readily in water and in polar organic solvents such as dimethyl sulfoxide. Aqueous solutions are clear and colorless at low concentrations. Because the peptide contains methionine, oxidation at the sulfur atom is a recognized degradation pathway, and handling notes usually call for protected, desiccated storage. Reported purity for research-grade lots is generally above 95 percent as measured by reversed-phase high-performance liquid chromatography.
The compound is registered in Russia as a pharmaceutical product, most commonly formulated as a nasal solution, and has been used in that setting since the 1990s. Outside that jurisdiction it is generally handled as a research chemical rather than an approved medicine. Regulatory status therefore differs sharply between countries, and material sold internationally may not correspond to the Russian pharmaceutical formulation. Documentation with commercial samples is typically limited to a certificate of analysis covering purity and identity, not clinical status or local legal classification.
Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. It corresponds to the ACTH(4-7) fragment extended at the C-terminus by a Pro-Gly-Pro tripeptide, an addition intended to slow enzymatic breakdown. The molecular formula is C37H51N9O10S and the molecular mass is approximately 814 daltons. In the literature it is often described as an ACTH(4-10) analog, although that label reflects a naming convention as much as a precise structural relationship. The compound was developed in Russia and remains most closely associated with that research tradition.
Pharmacokinetic accounts emphasize rapid breakdown. After intravenous dosing the intact peptide disappears from blood within minutes, and nasal delivery produces low but measurable concentrations. Metabolites rather than the parent molecule may account for part of the observed activity, although the relative contribution is unresolved. Dosing in the literature varies widely and no optimal schedule has been agreed. These gaps are regularly cited as a reason the findings have not produced broad clinical adoption beyond the original research setting.
Proposed mechanisms center on neurotrophic signaling rather than on classical melanocortin receptor activation. Rodent experiments have reported shifts in the expression of brain-derived neurotrophic factor and nerve growth factor after administration, together with changes in the associated receptor systems. Several authors argue that the peptide acts largely through its degradation products and their interaction with peptidergic pathways, but this remains a hypothesis rather than a settled finding. No single molecular target has been identified in a way that the field broadly accepts.
Published research covers ischemic stroke, traumatic brain injury, cognitive impairment, optic nerve conditions and attention-related measures. Much of the human evidence comes from small trials conducted in one country, which limits how far the results generalize. Animal models supply the larger share of the data, and effects seen in rodents do not transfer automatically to people. Reviews have noted that methodological reporting is often incomplete, making it difficult to pool results or compare treatment schedules across studies.
Dams – the Aztec in Tenochtitlan constructed great dams during the heyday of the Aztec Empire. Tenochtitlan, the capital of the Aztec empire, was first built on a small island that was located in the western section of Lake Texcoco in 1325 CE. The Aztec created various large artificial islands around the small island using a system that was similar to building the chinampas (floating gardens in the lake that was used to grow food for the cities' population). To provide drinking water to the cities' population of over a quarter of a million inhabitants, the Aztec built a system of dams that separated the salty waters of the lake from the rainwater that was accumulated during periods of heavy rains. The Aztec also used the dam to control the level of water in the lake and prevent their city from being flooded during times of heavy rains. To prevent flooding, the Aztec constructed an inner system of channels that helped to control the water level and held the level steady during flooding and periods of intense rains. Hernán Cortés, and the other Spanish conquistadors, destroyed these engineering marvels that the Aztec had developed during the previous 200 years. Dog breeds – Native American dogs believed to have been bred by indigenous Americans are the xochiocoyotl (coyote), xoloitzcuintli (known as xolo or Mexican hairless), chihuahua, Peruvian Hairless Dog, the Carolina Dog, Canadian Eskimo Dog, and the Alaskan Malamute.
=== EC 2.6.1: Transaminases === EC 2.6.1.1: aspartate transaminase EC 2.6.1.2: alanine transaminase EC 2.6.1.3: cysteine transaminase EC 2.6.1.4: glycine transaminase EC 2.6.1.5: tyrosine transaminase EC 2.6.1.6: leucine transaminase EC 2.6.1.7: kynurenine—oxoglutarate transaminase EC 2.6.1.8: deleted EC 2.6.1.9: histidinol-phosphate transaminase EC 2.6.1.10: deleted, included with EC 2.6.1.21, D-amino-acid transaminase EC 2.6.1.11: acetylornithine transaminase EC 2.6.1.12: alanine—oxo-acid transaminase EC 2.6.1.13: ornithine aminotransferase EC 2.6.1.14: asparagine—oxo-acid transaminase EC 2.6.1.15: glutamine—pyruvate transaminase EC 2.6.1.16: glutamine—fructose-6-phosphate transaminase (isomerizing) EC 2.6.1.17: succinyldiaminopimelate transaminase EC 2.6.1.18: β-alanine—pyruvate transaminase EC 2.6.1.19: 4-aminobutyrate transaminase EC 2.6.1.20: deleted EC 2.6.1.21: D-amino-acid transaminase EC 2.6.1.22: (S)-3-amino-2-methylpropionate transaminase EC 2.6.1.23: 4-hydroxyglutamate transaminase EC 2.6.1.24: diiodotyrosine transaminase EC 2.6.1.25: deleted, Now included with EC 2.6.1.24 diiodotyrosine transaminase EC 2.6.1.26: thyroid-hormone transaminase EC 2.6.1.27: tryptophan transaminase EC 2.6.1.28: tryptophan—phenylpyruvate transaminase EC 2.6.1.29: diamine transaminase EC 2.6.1.30: pyridoxamine—pyruvate transaminase EC 2.6.1.31: pyridoxamine—oxaloacetate transaminase EC 2.6.1.32: valine—3-methyl-2-oxovalerate transaminase EC 2.6.1.33: dTDP-4-amino-4,6-dideoxy-D-glucose transaminase EC 2.6.1.34: UDP-N-acetylbacillosamine transaminase EC 2.6.1.35: glycine—oxaloacetate transaminase EC 2.6.1.36: L-lysine 6-transaminase EC 2.6.1.37: (2-aminoethyl)phosphonate—pyruvate transaminase EC 2.6.1.38: histidine transaminase EC 2.6.1.39: 2-aminoadipate transaminase EC 2.6.1.40: (R)-3-amino-2-methylpropionate—pyruvate transaminase EC 2.6.1.41: D-methionine—pyruvate transaminase EC 2.6.1.42: branched-chain-amino-acid transaminase EC 2.6.1.43: aminolevulinate transaminase EC 2.6.1.44: alanine—glyoxylate transaminase EC 2.6.1.45: serine—glyoxylate transaminase EC 2.6.1.46: diaminobutyrate—pyruvate transaminase EC 2.6.1.47: alanine—oxomalonate transaminase EC 2.6.1.48: 5-aminovalerate transaminase EC 2.6.1.49: dihydroxyphenylalanine transaminase EC 2.6.1.50: glutamine—scyllo-inositol transaminase EC 2.6.1.51: serine—pyruvate transaminase EC 2.6.1.52: phosphoserine transaminase EC 2.6.1.53: Now EC 1.4.1.13, glutamate synthase (NADPH) EC 2.6.1.54: pyridoxamine-phosphate transaminase EC 2.6.1.55: taurine—2-oxoglutarate transaminase EC 2.6.1.56: 1D-1-guanidino-3-amino-1,3-dideoxy-scyllo-inositol transaminase EC 2.6.1.57: aromatic-amino-acid transaminase EC 2.6.1.58: phenylalanine(histidine) transaminase EC 2.6.1.59: dTDP-4-amino-4,6-dideoxygalactose transaminase EC 2.6.1.60: aromatic-amino-acid—glyoxylate transaminase EC 2.6.1.61: identical to EC 2.6.1.40, (R)-3-amino-2-methylpropionate—pyruvate transaminase EC 2.6.1.62: adenosylmethionine—8-amino-7-oxononanoate transaminase EC 2.6.1.63: kynurenine—glyoxylate transaminase EC 2.6.1.64: glutamine—phenylpyruvate transaminase EC 2.6.1.65: N6-acetyl-β-lysine transaminase EC 2.6.1.66: valine—pyruvate transaminase EC 2.6.1.67: 2-aminohexanoate transaminase EC 2.6.1.68: Now classified as EC 2.6.1.13, ornithine aminotransferase and EC 2.6.1.36, L-lysine 6-transaminase EC 2.6.1.69: identical to EC 2.6.1.11, ((acetylornithine transaminase))|identical to EC 2.6.1.11, acetylornithine transaminase EC 2.6.1.70: aspartate—phenylpyruvate transaminase EC 2.6.1.71: lysine—pyruvate 6-transaminase EC 2.6.1.72: D-4-hydroxyphenylglycine transaminase EC 2.6.1.73: methionine—glyoxylate transaminase EC 2.6.1.74: cephalosporin-C transaminase EC 2.6.1.75: cysteine-conjugate transaminase EC 2.6.1.76: diaminobutyrate—2-oxoglutarate transaminase EC 2.6.1.77: taurine—pyruvate aminotransferase EC 2.6.1.78: aspartate—prephenate aminotransferase EC 2.6.1.79: glutamate—prephenate aminotransferase EC 2.6.1.80: nicotianamine aminotransferase EC 2.6.1.81: succinylornithine transaminase EC 2.6.1.82: putrescine aminotransferase EC 2.6.1.83: LL-diaminopimelate aminotransferase EC 2.6.1.84: arginine—pyruvate transaminase EC 2.6.1.85: aminodeoxychorismate synthase EC 2.6.1.86: 2-amino-4-deoxychorismate synthase EC 2.6.1.87: UDP-4-amino-4-deoxy-L-arabinose aminotransferase EC 2.6.1.88: methionine transaminase EC 2.6.1.89: dTDP-3-amino-3,6-dideoxy-α-D-glucopyranose transaminase EC 2.6.1.90: dTDP-3-amino-3,6-dideoxy-α-D-galactopyranose transaminase EC 2.6.1.91: Identical to EC 2.6.1.34, UDP-N-acetylbacillosamine transaminase EC 2.6.1.92: UDP-4-amino-4,6-dideoxy-N-acetyl-β-L-altrosamine transaminase EC 2.6.1.93: neamine transaminase EC 2.6.1.94: 2′-deamino-2′-hydroxyneamine transaminase EC 2.6.1.95: neomycin C transaminase EC 2.6.1.96: 4-aminobutyrate—pyruvate transaminase EC 2.6.1.97: archaeosine synthase EC 2.6.1.98: UDP-2-acetamido-2-deoxy-ribo-hexuluronate aminotransferase EC 2.6.1.99: L-tryptophan—pyruvate aminotransferase EC 2.6.1.100: L-glutamine:2-deoxy-scyllo-inosose aminotransferase EC 2.6.1.101: L-glutamine:3-amino-2,3-dideoxy-scyllo-inosose aminotransferase EC 2.6.1.102: GDP-perosamine synthase EC 2.6.1.103: (S)-3,5-dihydroxyphenylglycine transaminase EC 2.6.1.104: 3-dehydro-glucose-6-phosphate—glutamate transaminase EC 2.6.1.105: lysine—8-amino-7-oxononanoate transaminase EC 2.6.1.106: dTDP-3-amino-3,4,6-trideoxy-α-D-glucose transaminase EC 2.6.1.107: β-methylphenylalanine transaminase EC 2.6.1.108: (5-formylfuran-3-yl)methyl phosphate transaminase EC 2.6.1.109: 8-amino-3,8-dideoxy-α-D-manno-octulosonate transaminase EC 2.6.1.110: dTDP-4-dehydro-2,3,6-trideoxy-D-glucose 4-aminotransferase EC 2.6.1.111: 3-aminobutanoyl-CoA transaminase EC 2.6.1.112: (S)-ureidoglycine—glyoxylate transaminase EC 2.6.1.113: putrescine—pyruvate transaminase EC 2.6.1.114: 8-demethyl-8-aminoriboflavin-5′-phosphate synthase EC 2.6.1.115: 5-hydroxydodecatetraenal 1-aminotransferase EC 2.6.1.116: 6-aminohexanoate aminotransferase EC 2.6.1.117: L-glutamine—4-(methylsulfanyl)-2-oxobutanoate aminotransferase EC 2.6.1.118: [amino-group carrier protein]-γ-(L-lysyl)-L-glutamate aminotransferase EC 2.6.1.119: vanillin aminotransferase
Surfactant protein D, also known as SP-D, is a lung surfactant protein part of the collagenous family of lectins called collectin. In humans, SP-D is encoded by the SFTPD gene and is part of the innate immune system. Each SP-D subunit is composed of an N-terminal domain, a collagenous region, a nucleating neck region, and a C-terminal lectin domain. Three of these subunits assemble to form a homotrimer, which further assemble into a tetrameric complex.
The current in an LED or other diodes rises exponentially with the applied voltage (see Shockley diode equation), so a small change in voltage can cause a large change in current. Current through the LED must be regulated by an external circuit such as a constant current source to prevent damage. LEDs are sensitive to voltage. They must be supplied with a voltage above their threshold voltage and a current below their rating. Current and lifetime change greatly with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs). Efficiency droop: The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents, which compromises LED lifetime. These effects put practical limits on the current through an LED in high power applications.
Sources: en.wikipedia.org
No one." Secretary of State Marco Rubio similarly claimed while testifying before Congress that no death resulted from the shutdown. Dr. Brooke Nichols, an infectious disease modeler working at Boston University, created an impact counter to estimate the life toll of funding cuts on various USAID health programs. As of 5 July 2025, the counter estimates that over 341,700 deaths have been caused by the funding discontinuation, over 230,700 of which are children.
Most aptamers are based on a specific oligomer sequence of 20-100 bases and 3-20 kDa. Some have chemical modifications for functional enhancements or compatibility with larger engineered molecular systems. DNA, RNA, XNA, and peptide aptamer chemistries can each offer distinct profiles in terms of shelf stability, durability in serum or in vivo, specificity and sensitivity, cost, ease of generation, amplification, and characterization, and familiarity to users. Typically, DNA- and RNA-based aptamers exhibit low immunogenicity, are amplifiable via Polymerase Chain Reaction (PCR), and have complex secondary structure and tertiary structure. DNA- and XNA-based aptamers exhibit superior shelf stability. XNA-based aptamers can introduce additional chemical diversity to increase binding affinity or greater durability in serum or in vivo. As 22 genetically encoded and over 500 naturally occurring amino acids exist, peptide aptamers, as well as antibodies, have much greater potential combinatorial diversity per unit length relative to the 4 nucleic acids in DNA or RNA. Chemical modifications of nucleic acid bases or backbones increase the chemical diversity of standard nucleic acid bases. Split aptamers are composed of two or more DNA strands that are pieces of a larger parent aptamer that has been broken in two by a molecular nick. The ability of each component strand to bind targets will depend on the location of the nick, as well as the secondary structures of the daughter strands. The presence of a target molecule supports the joining of DNA fragments.
== Industrial process design == In a typical scenario, an industrial process will use an extraction step in which solutes are transferred from the aqueous phase to the organic phase; this is often followed by a scrubbing stage in which unwanted solutes are removed from the organic phase, then a stripping stage in which the wanted solutes are removed from the organic phase. The organic phase may then be treated to make it ready for use again. After use, the organic phase may be subjected to a cleaning step to remove any degradation products; for instance, in PUREX plants, the used organic phase is washed with sodium carbonate solution to remove any dibutyl hydrogen phosphate or butyl dihydrogen phosphate that might be present.
Sources: en.wikipedia.org
一般不建议常温长期保存。多数说明指向 -20 °C 冷冻避光。常温运输通常被视为短期可接受，但会加快降解风险。
公开资料对此没有统一答案。普遍建议现配现用，或冷藏并在数日内用完。含甲硫氨酸的序列更易氧化，放置时间越长风险越高。
反相高效液相色谱是最常用的手段，配合质谱确认分子量。氨基酸组成分析和肽图分析可补充序列层面的验证。
Semax is based on the ACTH(4-10) fragment, a seven-amino-acid segment of adrenocorticotropic hormone. The synthetic peptide retains the core sequence while removing regions associated with endocrine activity. This modification is intended to isolate effects on the nervous system.