LC-MS raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-09-19 and is reviewed periodically as new material appears.
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.
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 |
|---|---|---|
| Storage temperature (reconstituted) | -20 °C to -80 °C | Exact condition depends on peptide, solvent, and stability data |
| Freeze-thaw stability | Limited number of cycles | Repeated cycles can increase aggregation and precipitation |
| Common degradation pathways | Hydrolysis, oxidation, deamidation | Relative rates depend on sequence, pH, and buffer |
| Container material | Low-binding polypropylene | Reduces adsorption loss for some peptides |
| Analytical method for stability | Reverse-phase HPLC | Monitors main peak loss and formation of impurity peaks |
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.
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.
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.
After a peptide is reconstituted, handling practices affect its chemical and physical stability over time. Aqueous solutions can support microbial growth unless they are prepared with aseptic technique or contain preservatives. Container material matters because peptides can adsorb to glass or plastic surfaces, reducing the amount available in solution. Repeated transfers increase exposure to air and potential contaminants, and temperature fluctuations can accelerate degradation. These factors are separate from the peptide's intrinsic sequence-based stability.
An automated insulin delivery system consists of three distinct components: a continuous glucose monitor to determine blood sugar levels, a pump to deliver insulin, and an algorithm that uses the data from the CGM and pump to determine needed insulin adjustments. In the United States, the Food and Drug Administration (FDA) allows each component to be approved independently, allowing for more rapid approvals and incremental innovation.
On the other hand, loss of control of cell death (resulting in excess apoptosis) can lead to neurodegenerative diseases, hematologic diseases, and tissue damage. Neurons that rely on mitochondrial respiration undergo apoptosis in neurodegenerative diseases such as Alzheimer's and Parkinson's. (an observation known as the "Inverse Warburg hypothesis"). Moreover, there is an inverse epidemiological comorbidity between neurodegenerative diseases and cancer. The progression of HIV is directly linked to excess, unregulated apoptosis. In a healthy individual, the number of CD4+ lymphocytes is in balance with the cells generated by the bone marrow; however, in HIV-positive patients, this balance is lost due to an inability of the bone marrow to regenerate CD4+ cells. In the case of HIV, CD4+ lymphocytes die at an accelerated rate through uncontrolled apoptosis, when stimulated. At the molecular level, hyperactive apoptosis can be caused by defects in signaling pathways that regulate the Bcl-2 family proteins. Increased expression of apoptotic proteins such as BIM, or their decreased proteolysis, leads to cell death and can cause a number of pathologies, depending on the cells where excessive activity of BIM occurs. Cancer cells can escape apoptosis through mechanisms that suppress BIM expression or by increased proteolysis of BIM.
The circadian oscillators in eukaryotes that have been studied function using a negative feedback loop in which proteins inhibit their own transcription in a cycle that takes approximately 24 hours. This is known as a transcription-translation-derived oscillator (TTO).(2) Without a nucleus, prokaryotic cells must have a different mechanism of keeping circadian time. In 1998, Ishiura et al. determined that the KaiABC protein complex was responsible for the circadian negative feedback loop in Synechococcus by mapping 19 clock mutants to the genes for these three proteins.(3) An experiment by Nakajima et al., in 2005, was able to demonstrate the circadian oscillation of the Synechococcus KaiABC complex in vitro. They did this by adding KaiA, KaiB, KaiC, and ATP into a test tube in the approximate ratio recorded in vivo. They then measured the levels of KaiC phosphorylation and found that it demonstrated circadian rhythmicity for three cycles without damping. This cycle was also temperature compensating. They also tested incubating mutant KaiC protein with KaiA, KaiB, and ATP. They found that the period of KaiC phosphorylation matched the intrinsic period of the cyanobacterium with the corresponding mutant genome. These results led them to conclude that KaiC phosphorylation is the basis for circadian rhythm generation in Synechococcus. (2)
Group specificity occurs when an enzyme will only react with molecules that have specific functional groups, such as aromatic structures, phosphate groups, and methyls. One example is pepsin, an enzyme that is crucial in digestion of foods ingested in our diet, that hydrolyzes peptide bonds in between hydrophobic amino acids, with recognition for aromatic side chains such as phenylalanine, tryptophan, and tyrosine. Another example is hexokinase, an enzyme involved in glycolysis that phosphorylates glucose to produce glucose-6-phosphate. This enzyme exhibits group specificity by allowing multiple hexoses (6 carbon sugars) as its substrate. Glucose is one of the most important substrates in metabolic pathways involving hexokinase due to its role in glycolysis, but is not the only substrate that hexokinase can catalyze a reaction with.
Sources: en.wikipedia.org
Cell membranes are generally impermeable to charged or large, polar molecules because of the lipophilic fatty acyl chains comprising their interior. Many biologically important molecules, including a number of pharmaceutical agents, are organic weak acids that can cross the membrane in their protonated, uncharged form but not in their charged form (i.e., as the conjugate base). For this reason the activity of many drugs can be enhanced or inhibited by the use of antacids or acidic foods. The charged form, however, is often more soluble in blood and cytosol, both aqueous environments. When the extracellular environment is more acidic than the neutral pH within the cell, certain acids will exist in their neutral form and will be membrane soluble, allowing them to cross the phospholipid bilayer. Acids that lose a proton at the intracellular pH will exist in their soluble, charged form and are thus able to diffuse through the cytosol to their target. Ibuprofen, aspirin and penicillin are examples of drugs that are weak acids.
This can be applied to find the best substrates for proteolytic enzymes. The substrate is displayed on the bacterial cell surface between an affinity ligand and the scaffold, and the kinetics of substrate proteolysis is measured using FACS. Bacterial display can be used to find peptides which bind to specific cells e.g. breast cancer cells or stem cells. Displayed proteins are fluorescently tagged with GFP, so binding interactions between peptides and target cells can be seen by flow cytometry. Control samples are required in order to measure fluorescence levels in the absence of displayed peptides. Samples are also required which don’t contain displayed peptides, but contain mammalian cells and bacterial cells (including the scaffold). Vaccine delivery is a very common application of bacterial surface display. There are two types of live bacterial vaccines that can be made:
Accelerator mass spectrometry (AMS) is a form of mass spectrometry that accelerates ions to extraordinarily high kinetic energies before mass analysis. The special strength of AMS among the different methods of mass spectrometry is its ability to separate a rare isotope from an abundant neighboring mass ("abundance sensitivity", e.g. 14C from 12C). The method suppresses molecular isobars completely and in many cases can also separate atomic isobars (e.g. 14N from 14C). This makes possible the detection of naturally occurring, long-lived radio-isotopes such as 10Be, 36Cl, 26Al and 14C. (Their typical isotopic abundance ranges from 10−12 to 10−18.) AMS can outperform the competing technique of decay counting for all isotopes where the half-life is long enough. Other advantages of AMS include its short measuring time as well as its ability to detect atoms in extremely small samples.
These drugs have been derived from NSAIDs. The cyclooxygenase enzyme inhibited by NSAIDs was discovered to have at least two different versions: COX-1 and COX-2. Research suggested most of the adverse effects of NSAdiated by blocking the COX-1 (constitutive) enzyme, with the analgesic effects being mediated by the COX-2 (inducible) enzyme. Thus, the COX-2 inhibitors were developed to inhibit only the COX-2 enzyme (traditional NSAIDs block both versions in general). These drugs (e.g., rofecoxib, celecoxib, and etoricoxib) are equally effective analgesics when compared with NSAIDs, but cause less gastrointestinal hemorrhage in particular. After widespread adoption of the COX-2 inhibitors, it was discovered that most of the drugs in this class increase the risk of cardiovascular events by 40% on average. This led to the withdrawal of rofecoxib and valdecoxib, and warnings on others. Etoricoxib seems relatively safe, with the risk of thrombotic events similar to that of non-coxib NSAID diclofenac.
Division of analytical chemistry and laboratory of bio-electrochemical biosensor research function in this department. The division conducts research in the area of methods of electrochemical analysis using chemically modified electrodes and biosensors. The head of the department is Professor Gennady A. Evtyugin, doctor of Science in chemistry. The Department conducts research in the following fields:
Sources: en.wikipedia.org
In Indonesia, the National Transportation Safety Committee (NTSC; Indonesian: Komite Nasional Keselamatan Transportasi, KNKT) is responsible for the investigation of incidents and accidents, including air accidents. Its aim is the improvement of transportation safety, not just aviation, in Indonesia. Created in 1999 in Italy, the Agenzia Nazionale per la Sicurezza del Volo (ANSV), has two main tasks: conducting technical investigations for civil aviation aircraft accidents and incidents, while issuing safety recommendations as appropriate; and conducting studies and surveys aimed at increasing flight safety. The organization is also responsible for establishing and maintaining the "voluntary reporting system". Although not under the supervision of the Ministry of Infrastructure and Transport, the ANSV is a public authority under the oversight of the Presidency of the Council of Ministers of Italy.
Although most yeasts have only a single actin gene, higher eukaryotes, in general, express several isoforms of actin encoded by a family of related genes. Mammals have at least six actin isoforms coded by separate genes, which are divided into three classes – alpha, beta, and gamma – according to their isoelectric points. In general, alpha actins are found in muscle (α-skeletal, α-aortic smooth, α-cardiac), whereas beta and gamma isoforms are prominent in non-muscle cells (β-cytoplasmic, γ1-cytoplasmic, γ2-enteric smooth). Although the amino acid sequences and in vitro properties of the isoforms are highly similar, these isoforms cannot completely substitute for one another in vivo. Plants contains more than 60 actin genes and pseudogenes. The typical actin gene has an approximately 100-nucleotide 5' UTR, a 1200-nucleotide translated region, and a 200-nucleotide 3' UTR. The majority of actin genes are interrupted by introns, with up to six introns in any of 19 well-characterised locations. The high conservation of the family makes actin the favoured model for studies comparing the introns-early and introns-late models of intron evolution.
Annals of Clinical Biochemistry is a bimonthly peer-reviewed scientific journal covering all aspects of clinical biochemistry. The editor-in-chief is Michael J Murphy (University of Dundee). It was established 1960 and is published by SAGE Publications on behalf of The Association for Clinical Biochemistry and Laboratory Medicine. The journal is abstracted and indexed in: According to the Journal Citation Reports, its 2012 impact factor is 1.922, ranking it 12th out of 31 journals in the category "Medical Laboratory Technology". Official website
The American Society of Plant Biologists (ASPB) is a non-profit professional society for research and education in plant science. It was founded in 1924 as the American Society of Plant Physiologists (ASPP); the name was changed in 2001. Membership in the society is open to any person from any country who deals with physiology, molecular biology, environmental biology, cell biology and plant biophysics or related issues. It has over 4,000 members worldwide. The society publishes the peer-reviewed journals Plant Physiology (1926–) and The Plant Cell (1989–) as well as ASPB News. The American Society of Plant Biologists also has partnered with the Society for Experimental Biology, and John Wiley & Sons to publish an online-only science journal Plant Direct. In 2000, it published the first edition of the textbook Biochemistry & Molecular Biology of Plants. The first President of the Society was Charles Albert Shull (1924–1925), with founder R. B. Harvey as Secretary-Treasurer. Other presidents of the Society include Harry Beevers (1961–1962), Aubrey Naylor (1960–1961), and Katayoon Dehesh (2021-2022). The first woman to be president of the society was Elisabeth Gantt (1988–1989).
5-Hydroxytryptophan (5-HTP), used medically as oxitriptan, is a naturally occurring amino acid and chemical precursor as well as a metabolic intermediate in the biosynthesis of the neurotransmitter serotonin. 5-HTP can be manufactured and used as a drug and supplement with the INNTooltip International Nonproprietary Name oxitriptan. Brand names include Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum. As a drug, it is used in the treatment of depression and for certain other indications. 5-HTP is produced from the amino acid tryptophan through the action of the enzyme tryptophan hydroxylase. Tryptophan hydroxylase is one of the biopterin-dependent aromatic amino acid hydroxylases. Production of 5-HTP is the rate-limiting step in 5-HT (serotonin) synthesis. 5-HTP is normally rapidly converted to 5-HT by amino acid decarboxylase.
Sources: en.wikipedia.org
No single time applies to all peptides. Storage life depends on sequence, solvent, concentration, and temperature. Stability should be determined experimentally or taken from supplier data for the specific lot.
Refreezing is possible but repeated cycles are discouraged. Each freeze-thaw step may increase aggregation or loss. Aliquoting before freezing reduces the number of cycles.
Cloudiness, visible particles, color changes, or new peaks in chromatography can indicate degradation. A loss of expected activity in an assay may also suggest a problem. Confirmatory methods include LC-MS and purity analysis.
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.