A practical reference on deamidation: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-01-15. Anything still debated is marked as such rather than presented as settled.
After a peptide solution is prepared, its handling conditions influence how long it remains suitable for use. Solutions are typically separated into small portions to avoid repeated freeze-thaw cycles, which can promote aggregation or precipitation. Containers are chosen to minimize adsorption, especially for peptides that are hydrophobic or present at low concentration. Some laboratories use low-binding plastic tubes or add a carrier protein, although carrier addition can interfere with later analysis. Records usually note the solvent, date, and storage temperature for traceability.
Storage stability of a reconstituted peptide depends on concentration, pH, buffer composition, and the presence of oxygen or microbial contaminants. Short-term storage is often at refrigerated temperatures, while longer-term storage may use freezing at -20 °C or -80 °C. Repeated warming and cooling can cause losses through adsorption or aggregation, so aliquots are preferred. Light-sensitive peptides require protection from ambient light. Sterile filtration may be used when microbial control is needed, but filters can adsorb peptides and reduce recovery.
Quality control after reconstitution usually includes visual inspection and instrumental analysis. A clear, particle-free solution is generally expected, but color and clarity can vary with sequence and buffer. Chromatographic separation can detect degradation products, while mass confirmation verifies molecular identity. pH measurement and osmolality checks may be relevant for certain applications. Documentation of lot number, solvent, and storage history supports reproducibility and helps distinguish preparation artifacts from sample degradation. Temperature logs and freeze-thaw counts add further context when results are reviewed.
Analytical checks help determine whether a reconstituted peptide matches its expected identity and purity; reverse-phase high-performance liquid chromatography separates components by hydrophobicity and can reveal degradation products or impurities. Mass spectrometry provides a mass measurement that supports sequence identity when compared with the theoretical value. Ultraviolet absorbance at 280 nm can estimate concentration for peptides containing tryptophan or tyrosine, though sequence-dependent extinction coefficients are needed. For shorter or non-aromatic peptides, other methods such as amino acid analysis may be required. These techniques describe the material rather than guarantee its biological effect.
Cloudiness, particles, or gel formation after reconstitution can signal incomplete dissolution, aggregation, or contamination. A clear solution is not proof of purity, and a cloudy one is not always unusable if the peptide is designed to form suspensions. pH measurement can identify whether the solution matches the intended range, and buffer exchange may be needed when the original solvent is incompatible. Sterile filtration is sometimes used for microbial control, but filters can adsorb peptides and reduce concentration. Documentation of lot number, solvent, volume, date, and storage condition supports later traceability in laboratory records.
| Property | Value | Notes |
|---|---|---|
| Appearance | Clear to slightly opalescent | Opalescence may indicate aggregation or undissolved material |
| Typical pH range | 3–7 for many peptides | Depends on sequence and buffer; measured after dissolution |
| Storage temperature (short term) | 2–8 °C | Refrigerated; limit repeated warming |
| Storage temperature (long term) | -20 °C or -80 °C | Freezing recommended for many research peptides |
| Common analytical method | RP-HPLC with UV detection | Purity and degradation profile can be monitored |
Analytical checks can detect changes in a reconstituted stock over time. Reverse-phase high-performance liquid chromatography can show loss of main peak, new impurity peaks, or altered retention. Mass spectrometry confirms molecular identity and can reveal modifications. Visual inspection for particles, color change, or turbidity provides a simple first check. If a solution shows signs of degradation or contamination, it is typically discarded rather than re-purified in a routine laboratory.
Once a peptide is dissolved, its solution is generally less stable than the dry powder. Chemical pathways such as hydrolysis, oxidation, and deamidation can alter the molecule, while physical processes can form aggregates or cause adsorption to container walls. The rate depends on pH, buffer composition, temperature, concentration, and the specific sequence. Aqueous stocks are therefore kept cold and used within a defined period. Stability testing is usually performed for each peptide rather than assumed from a general rule.
Cold storage slows most degradation but does not stop it. Reconstituted solutions are commonly divided into aliquots and held at -20 °C or -80 °C, depending on the peptide. Repeated freeze-thaw cycles can promote aggregation or precipitation, so single-use aliquots are preferred. Some peptides tolerate refrigeration for short intervals, while others require freezing immediately. Light-sensitive residues may need amber or foil-wrapped containers. The optimal condition remains peptide-specific and should be supported by stability data.
Storage conditions for reconstituted peptides are product-specific. Cool temperatures slow many degradation pathways, but freezing can concentrate solutes and promote aggregation. Light exposure can oxidize susceptible residues such as methionine, cysteine, or tryptophan. Oxygen in headspace can contribute to oxidation, while acidic or basic pH can drive hydrolysis and deamidation. The best storage condition for a given sequence is often determined empirically because general rules do not capture all sequence-specific effects.
Quality control of reconstituted peptides combines visual inspection with instrumental analysis. A clear solution does not prove correct identity or purity, and a cloudy solution does not always indicate failure. Reverse-phase high-performance liquid chromatography can separate the peptide from related impurities, while mass spectrometry confirms molecular mass and detects modifications. pH measurement and osmolality checks provide additional information about the solution environment, and documentation of lot number, solvent, and storage history supports traceability.
There is adequate evidence citing case after case of African control of segments of the trade. Several African nations such as the Calabar and other southern parts of Nigeria had economies depended solely on the trade. African peoples such as the Imbangala of Angola and the Nyamwezi of Tanzania would serve as middlemen or roving bands warring with other African nations to capture Africans for Europeans. Several historians have made important contributions to the global understanding of the African side of the Atlantic slave trade. By arguing that African merchants determined the assemblage of trade goods accepted in exchange for slaves, many historians argue for African agency and ultimately a shared responsibility for the slave trade. In 1999, President Mathieu Kérékou of Benin issued a national apology for the central role Africans played in the Atlantic slave trade. Luc Gnacadja, minister of environment and housing for Benin, later said: "The slave trade is a shame, and we do repent for it." Researchers estimate that 3 million slaves were exported out of the Slave Coast bordering the Bight of Benin. President Jerry Rawlings of Ghana also apologized for his country's involvement in the slave trade. The issue of an apology is linked to reparations for slavery and is still being pursued by entities across the world. For example, the Jamaican Reparations Movement approved its declaration and action plan. In 2007, British Prime Minister Tony Blair made a formal apology for Great Britain's involvement in slavery.
== General == Human Development Index (2021): Thailand ranked 66 of 191 countries. Satisfaction with Life Index: Ranked 76 of 178 countries. Where-to-be-born Index: Thailand ranked 50 of 80 countries.
== Scope == Medical genetics encompasses many different areas, including clinical practice of physicians, genetic counselors, and nutritionists, clinical diagnostic laboratory activities, and research into the causes and inheritance of genetic disorders. Examples of conditions that fall within the scope of medical genetics include birth defects and dysmorphology, intellectual disabilities, autism, mitochondrial disorders, skeletal dysplasia, connective tissue disorders, cancer genetics, and prenatal diagnosis. Medical genetics is increasingly becoming relevant to many common diseases. Overlaps with other medical specialties are beginning to emerge, as recent advances in genetics are revealing etiologies for morphologic, endocrine, cardiovascular, pulmonary, ophthalmologist, renal, psychiatric, and dermatologic conditions. The medical genetics community is increasingly involved with individuals who have undertaken elective genetic and genomic testing.
Microscopy is a category of characterization techniques which probe and map the surface and sub-surface structure of a material. These techniques can use photons, electrons, ions or physical cantilever probes to gather data about a sample's structure on a range of length scales. Some common examples of microscopy techniques include:
Sources: en.wikipedia.org
== Hunger pangs == The physical sensation of hunger is related to the contractions of the muscles of the empty stomach. Peristalsis takes place even when the stomach is empty, and these contractions—sometimes called hunger pangs once they become severe—are believed to be triggered by high concentrations of the ghrelin hormone. The migrating motor complex is a pattern of hunger contractions that takes place in the hungry stomach and gut; they are correlated in time with subjective sensations of hunger and are even responsible for the rumbling associated with a hungry stomach. In contrast, the hormones peptide YY and leptin can have an opposite effect on the appetite, causing the sensation of being full. Ghrelin can be released if blood sugar levels dip too low—a condition called hypoglycemia that can result from long periods without eating. Stomach contractions from hunger can be especially severe and painful in children and young adults. Hunger pangs can be made worse by irregular meals. People who cannot afford to eat more than once a day sometimes refuse one-off additional meals, because if they do not eat at around the same time on the next days, they may suffer extra severe hunger pangs. Older people may feel less violent stomach contractions when they get hungry, but still suffer the secondary effects resulting from low food intake: these include weakness, irritability and decreased concentration. Prolonged lack of adequate nutrition also causes increased susceptibility to disease and reduced ability for the body to heal.
In contrast to counter current chromatography (see above), periodic counter-current chromatography (PCC) uses a solid stationary phase and only a liquid mobile phase. It thus is much more similar to conventional affinity chromatography than to counter current chromatography. PCC uses multiple columns, which during the loading phase are connected in line. This mode allows for overloading the first column in this series without losing product, which already breaks through the column before the resin is fully saturated. The breakthrough product is captured on the subsequent column(s). In a next step the columns are disconnected from one another. The first column is washed and eluted, while the other column(s) are still being loaded. Once the (initially) first column is re-equilibrated, it is re-introduced to the loading stream, but as last column. The process then continues in a cyclic fashion.
== In protein dynamics == The significance of peptide plane flips in the dynamics of the native state has been inferred in some proteins by comparing crystal structures of the same protein in multiple conformations. For example, peptide flips have been described as significant in the catalytic cycle of flavodoxin and in the formation of amyloid structures, where their ability to provide a low-energy pathway between beta sheet and the so-called alpha sheet conformation is suggested to facilitate the early stages of amyloidogenesis. Peptide plane flipping may also be significant in the early stages of protein folding.
== Typical technique == A sample is introduced, either manually or with an autosampler, into a sample loop of known volume. A buffered aqueous solution known as the mobile phase carries the sample from the loop onto a column that contains some form of stationary phase material. This is typically a resin or gel matrix consisting of agarose or cellulose beads with covalently bonded charged functional groups. Equilibration of the stationary phase is needed in order to obtain the desired charge of the column. If the column is not properly equilibrated the desired molecule may not bind strongly to the column. The target analytes (anions or cations) are retained on the stationary phase but can be eluted by increasing the concentration of a similarly charged species that displaces the analyte ions from the stationary phase. For example, in cation exchange chromatography, the positively charged analyte can be displaced by adding positively charged sodium ions. The analytes of interest must then be detected by some means, typically by conductivity or UV/visible light absorbance. Control an IC system usually requires a chromatography data system (CDS). In addition to IC systems, some of these CDSs can also control gas chromatography (GC) and HPLC.
Grain-based feeds such as corn and barley produce up to one third less methane gas in cattle than grass fed cattle. By impeding methane production, Asparagopsis increases the efficiency of ruminant digestion in livestock to improve productivity.
Sources: en.wikipedia.org
The CODATA recommended value of a proton's charge radius is 8.4075(64)×10−16 m. The radius of the proton measured by electron–proton scattering differs from the value measured via the Lamb shift in muonic hydrogen (an exotic atom made of a proton and a negatively charged muon). As a muon is 200 times heavier than an electron, resulting in a smaller atomic orbital, it is much more sensitive to the proton's charge radius and thus allows a more precise measurement. Subsequent improved scattering and electron-spectroscopy measurements agree with the new small radius. Work continues to refine and check this new value. A third kind of high precision measurement agrees most closely with the value given by the muonic hydrogen spectroscopy but unexplained differences remain. The exact nature of what these measurement mean has also been questioned.
=== Aquaporin-1 === Aquaporin-1 (Aqp1) from the human red blood cell has been solved by electron crystallography to 3.8 Å resolution (PDB: 1FQY). The aqueous pathway is lined with conserved hydrophobic residues that permit rapid water transport. Water selectivity is due to a constriction of the inner pore diameter to about 3 Å over the span of a single residue, superficially similar to that in the glycerol facilitator of E. coli. Several other more recently resolved crystal structures are available in RCSB, including but not limited to: PDB: 4CSK, 1H6I, 1IH5.
==== Monensin ==== In 1980, Still and coworkers reported the total synthesis of monensin, a complex polyether natural product that acts as an ionophore. One of the key steps in this route is the late-stage union of two advanced fragments via an intermolecular aldol reaction. In this reaction, low-temperature deprotonation of the methyl ketone with lithium diisopropylamide formed the kinetic enolate which then underwent transmetalation upon the addition of magnesium bromide. Subsequent addition of the aldehyde component initiated a diastereoselective aldol reaction, forming the desired beta-hydroxyketone in 75% yield as a 3:1 mixture of diastereomers. Notably, this instance of acyclic stereocontrol is consistent with the Cram-Felkin-Anh model for the addition of nucleophiles to an aldehyde bearing an existing stereocenter in the alpha position.
Vivien Jess. Learning Centre Manager, Education Training Service. For services to Defence and to the community in Northern Ireland. Dr Terry Martin John. Lately General Practitioner, The Firs Medical Centre, London Borough of Waltham Forest and lately Chair of International Committee, British Medical Association. For services to Medicine. Frances Barbara Johnson. Learning Support Assistant, Dame Tipping Church of England Primary School, Romford, London Borough of Havering. For services to Education. Louis Connor Johnson. For services to the community in Wolverhampton, West Midlands. Hilary Johnston. Founder, Cwtch Baby Bank. For services to Mothers and Babies in South East Wales. Monica Ann Johnston. Admission/Discharge Co-ordinator, Neurosciences, Belfast Health and Social Care. For services to Nursing and to the community in Northern Ireland. Anne Jones. For services to the community in Neston, Cheshire. Patricia Ellen Jones. For services to the community in Nailsworth, Gloucestershire. Sundeep Kaur. Director, United Sikhs. For services to the community in the West Midlands during Covid-19. Lisa Michelle Kay. For charitable services to Ukrainian Refugees and to the community in Solihull, West Midlands. Coral June Kelham. For services to the community in Barrow upon Soar, Leicestershire. Anne Marie Kelly. Lately Regional Office Manager, Northern Ireland Organ Donor Service. For services to Organ Donation and Transplantation in Northern Ireland. Richard Kennell. Chief Executive Officer, SOFEA. For services to Social Inclusion and to Alleviating Food Poverty.
Sources: en.wikipedia.org
Refrigeration is common for short-term use, while freezing at -20 °C or -80 °C is common for longer periods. Aliquots reduce repeated temperature changes. Exact conditions depend on the peptide and buffer.
Repeated freeze-thaw cycles can cause aggregation, precipitation, or adsorption losses. Dividing a solution into single-use portions limits those changes. The practice also makes handling more consistent.
Undissolved powder, aggregated peptide, or precipitated buffer salts can produce visible particles. Some particles appear only after freezing or pH changes. Filtration and analytical checks can help identify the source.
Short-term storage is often under refrigeration, while longer storage may use freezing at -20 °C or lower. The choice depends on peptide stability and the solvent. Dividing the solution into aliquots reduces repeated temperature changes.