methionine sulfoxide comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2025-09-20. Numbers and descriptions here follow the published literature rather than marketing material.
Purity assessment relies mainly on reversed-phase high-performance liquid chromatography, which separates the target heptapeptide from truncated sequences, deletion analogues, and oxidised forms. Mass spectrometry, usually coupled to liquid chromatography, confirms identity through the expected molecular ion and reveals modifications such as methionine sulfoxide formation. Amino acid analysis can verify composition, and tandem mass spectrometry supports sequence confirmation. Ultraviolet detection near 254 to 280 nanometres is convenient because the phenylalanine and histidine residues absorb in that region. Nuclear magnetic resonance is rarely used for routine release testing.
Common degradation pathways include oxidation of the methionine side chain, hydrolysis of the peptide backbone, and aggregation under unfavourable pH or concentration. Stability studies typically monitor the main peak by chromatography and report total related substances as a percentage. Because no official monograph exists, acceptance criteria vary between laboratories, and reported purity values are not directly comparable across suppliers. Analysts therefore document the method, column, and detection wavelength alongside each result, and open questions remain about how much biological activity the oxidised forms retain.
稳定性主要由水解与氧化两条路径支配。肽键在中性或弱酸性条件下相对稳定，遇到强碱或长时间高温则明显断裂；甲硫氨酸侧链容易被氧化成亚砜，使主峰前移并拉低实际含量。金属离子、光照和反复冻融会进一步促进降解或聚集。冻干粉在低温避光条件下可存放较长时间，配制后的水溶液通常需要冷藏并尽快用完。
纯度评估以反相高效液相色谱为主，通过主峰面积百分比给出粗略结果，再配合电喷雾质谱核对分子量。氨基酸分析可验证组成比例，手性色谱或毛细管电泳用于检查残基构型。常见杂质包括缺失序列的短肽、氧化产物与二聚体。由于多数市售品不附带完整检验报告，独立第三方检测常被用来核实标称值。
| Property | Value | Notes |
|---|---|---|
| Typical analytical method | Reversed-phase HPLC with UV detection | Separates target peptide from truncated and oxidised forms |
| Identity confirmation | LC-MS or ESI-MS | Compares observed and calculated molecular ion |
| Primary degradation route | Methionine oxidation | Forms the sulfoxide; monitored as an early-eluting peak |
| Short-term storage | 2 to 8 degrees Celsius | Applies to working vials and reconstituted portions |
| Common synonyms | ACTH(4–10) analogue, MEHFPGP | Descriptive names used in laboratory catalogues |
Fox, Sidney W. (1957). Introduction to protein chemistry. New York: Wiley. Fox, Sidney W. (1965). The origins of prebiological systems and of their molecular matrices. New York: Acad. Pr. Fox, Sidney W.; Duane L Rohlfing, Aleksandr Ivanovich Oparin (1972). Molecular evolution: prebiological and biological. New York: Plenum Press. Fox, Sidney W., Klaus Dose; with a foreword by A. Oparin (1977). Molecular evolution and the origin of life (Rev. ed. ed.). New York: M. Dekker. Fox, Sidney W. (1984). Individuality and determinism: chemical and biological bases. New York: Plenum Press. Ho, edited by Mae-Wan; Fox, Sidney W. (1988). Evolutionary processes and metaphors. Chichester: Wiley. pp. 333. ISBN 0-471-91801-6. Fox, Sidney W. (1988). The emergence of life: Darwinian evolution from the inside. Basic Books.
On 3 May, the day after the government was defeated at the 1997 general election, Heseltine suffered an attack of angina and had a tube inserted into an artery; at 64, and twenty years older than the new prime minister, he declined to stand for the Conservative Party leadership again. However, he was less unpopular with eurosceptics than Clarke, and on the third ballot of the subsequent leadership election Clarke, facing imminent defeat by William Hague, offered to stand aside in Heseltine's favour, but he declined on medical advice. He became active in promoting the benefits for Britain of joining the Single European Currency, appearing on the same stage as Tony Blair, Gordon Brown and Robin Cook as part of an all-party campaign to promote Euro membership. He was also made a Member of the Order of the Companions of Honour in the 1997 resignation Honours List. In November 1999 Heseltine was invited by Hague to be the Conservative candidate for the new position of Mayor of London (in place of Jeffrey Archer who had had to stand down because of scandal), but he declined. In the interim Shadow Cabinet of John Major he served as Deputy Leader of the Opposition, Shadow Chancellor of the Duchy of Lancaster and Shadow Secretary of State for Trade and Industry.
== Transmission == Citrus greening was originally thought to be a viral disease, but is caused by a bacterium, carried by insect vectors. Infection can arise in various climates and is often associated with different species of psyllid insects. For example, citrus crops in Africa become infected under cool conditions as the bacteria are transmitted by the African citrus psyllid Trioza erytreae, an insect that favors cool and moist conditions for optimal activity. Citrus crops in Asia, however, are often infected under warm conditions as the bacteria are transmitted by the Asian citrus psyllid Diaphorina citri. The young larval stage is the most suitable for acquisition of ca. L. asiaticus by the Asian citrus psyllid Diaphorina citri, and some cultivars show greater efficiency in transmitting the disease to the vector than others. Temperature also shows a great influence in the parasite-host relationship between the bacteria and the insect vector, affecting how it is acquired and transmitted by the insects. The causative agents are fastidious phloem-restricted, Gram-negative bacteria in the gracilicutes clade. The Asian form, ca. L. asiaticus is heat tolerant. This means the greening symptoms can develop at temperatures up to 35 °C (95 °F). The African form, ca. L. africanus, and American form, ca. L. americanus, are heat sensitive, thus symptoms only develop when the temperature is in the range 20–25 °C (68–77 °F). Although T. erytreae is the natural vector of African citrus greening and D.
== Clinical significance == Patients with chronic diarrhea due to bile acid malabsorption have been shown to have reduced fasting FGF19. Surgical resection of the ileum (as often occurs in Crohn's disease) will reduce bile acid absorption and remove the stimulus for FGF19 production. In primary bile acid diarrhea, absorption of bile acids is usually normal, but defective FGF19 production can produce excessive bile acid synthesis, as shown by increased levels of 7α-hydroxy-4-cholesten-3-one, and excessive bile acid fecal loss, indicated by reduced SeHCAT retention. This was confirmed in a prospective study of patients with chronic diarrhea, where the predictive value for FGF19 in diagnosis of primary bile acid diarrhea and response to bile acid sequestrants was demonstrated. FGF19 is also found in the liver of patients with cholestasis. It can be synthesised in the gall-bladder and secreted into bile. FGF19 is expressed in around half of hepatocellular carcinomas and was associated with larger size, early recurrence and poor prognosis. Patients with the metabolic syndrome, non-alcoholic fatty liver disease and insulin resistance have reduced levels of FGF19. FGF19 increases to normal values in obese patients who undergo Roux-en-Y gastric bypass and other types of bariatric surgery.
Sources: en.wikipedia.org
=== Discovery === Darmstadtium was first discovered on November 9, 1994, at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung, GSI) in Darmstadt, Germany, by Peter Armbruster and Gottfried Münzenberg, under the direction of Sigurd Hofmann. The team bombarded a lead-208 target with accelerated nuclei of nickel-62 in a heavy ion accelerator and detected a single atom of the isotope darmstadtium-269:
== History == Occurrence of iron-containing red protein in bovine milk was reported as early as in 1939; however, the protein could not be properly characterized because it could not be extracted with sufficient purity. Its first detailed studies were reported around 1960. They documented the molecular weight, isoelectric point, optical absorption spectra and presence of two iron atoms per protein molecule. The protein was extracted from milk, contained iron and was structurally and chemically similar to serum transferrin. Therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. The antibacterial action of lactoferrin was also documented in 1961, and was associated with its ability to bind iron. Recombinant lactoferrin production began in the 1990s with the expression of human lactoferrin (hLF) in microbial hosts, notably filamentous fungi such as Aspergillus oryzae, achieving yields exceeding 2 g/L in some cases. Yeast expression systems, particularly Pichia pastoris, were subsequently developed for scalable and cost-effective production. In a landmark development, Sydney-based biotechnology company All G became the first in the world to gain regulatory approval to sell recombinant bovine lactoferrin in China, achieved in November 2024 through precision fermentation (animal-free, microbe-based production).
Nicotine replacement therapy (NRT) products, including gums, patches, and lozenges, deliver the compound in slower, lower doses that are less addictive and are used medically to help people quit smoking. Synthetic derivatives of nicotine, such as varenicline, act as partial agonists at nicotinic receptors and are also used as smoking cessation aids. Nicotine itself is not classified as a carcinogen by either the International Agency for Research on Cancer or the Surgeon General of the United States. At high doses it can cause nicotine poisoning and respiratory paralysis. Nicotine is also a known teratogen, associated with adverse developmental effects during pregnancy, and may impair adolescent neurodevelopment, though the extent of this effect in humans remains debated.
Sources: en.wikipedia.org
Dry powder is usually kept at about -20 degrees Celsius for long-term storage and at 2 to 8 degrees Celsius for short working periods. Containers should stay sealed and protected from light and moisture to limit degradation.
Oxidation of the methionine residue to the sulfoxide is a frequently reported change, and it usually appears as an earlier-eluting peak in reversed-phase chromatography. Backbone hydrolysis products can also accumulate in aqueous solution.
Liquid chromatography coupled with mass spectrometry is the usual approach, because the observed molecular ion can be compared with a calculated mass of about 813.9 Da. Retention time alone does not establish identity.
电喷雾或基质辅助激光解吸电离质谱是常用手段，测得的质子化离子质荷比可换算为分子量。结果与理论值落在合理误差内，才支持结构一致的判断。