Educational guides and overviews on research peptides, what they are and how they're studied in the laboratory. For research use only.
A 0.22 µm rating is a retention performance claim tied to a defined bacterial challenge, not a guarantee and not a sieve. This guide covers membrane binding losses, what filtration fails to remove, what it can add, and why a subvisible particle count is a property of the instrument as much as the sample.
Read moreTB-500 is the N-terminally acetylated 17–23 fragment of thymosin β4. Most of the biology attributed to it was measured on the unacetylated peptide or the full-length protein, and the one study that tested the acetylated form directly found no significant activity for it. What has been measured, and what has not.
Read moreWhat a beta-arrestin recruitment assay physically measures across BRET, enzyme complementation and imaging formats, how a bias factor is calculated from transduction coefficients with the arithmetic and error propagation shown, and why the resulting number is a property of the assay system.
Read moreAn EC50 from a cAMP assay is not a property of the compound. It is that compound read through one receptor at one density, in one cell background, at one read time, with a phosphodiesterase inhibitor in the buffer. Gs coupling, IBMX, HTRF and Alpha formats, receptor reserve, and the arithmetic of amplification.
Read moreA cell-based number describes a system, not a molecule. What serum binding, labware adsorption, medium chemistry, passage drift, mycoplasma and cell line identity each do to a peptide result — with the arithmetic worked, and the difference between evidence and convention stated.
Read moreAn EC50 is a parameter of a fitted curve, not a measurement. This guide covers four-parameter logistic fitting, what a Hill slope away from unity indicates, how to read a confidence interval on potency, and why comparing EC50 values across papers is usually invalid.
Read moreAn ELISA measures immunoreactivity, not molar concentration. This guide covers what separates the two for peptides: sandwich versus competitive formats, epitope availability, cross-reactivity with fragments and precursors, matrix interference, and standard curve design.
Read moreA binding constant is a subtraction between two counts, on a system assumed to be at equilibrium, at a concentration assumed to be the one on the tube. How saturation and competition differ, what the nonspecific blank removes, why Cheng-Prusoff is an approximation, and why incubations are too short.
Read moreA dose-response curve makes three separable claims, and each can fail on its own. What n actually counts, which statistic the error bars show, how the choice of 100% moves the plateaus, what a truncated axis magnifies, and why a curve without a top plateau reports an EC50 that was never measured.
Read moreA panel of "no significant activity" entries is a bounded negative, not proof of specificity. This guide works through panel composition, the arithmetic linking single-point percent inhibition to IC50, how hit thresholds are chosen, and why a selectivity ratio depends on which value is the denominator.
Read moreA phospho-blot reports antibody retained on a membrane, not a signaling state. This guide covers how phospho-specific antibodies are validated, why loading controls are themselves measurements, how to establish a linear range from a dilution series, and the arithmetic showing what saturation does to a fold change.
Read moreAn ITC instrument measures heat and nothing else; every other number on the report is a fitted parameter. What the c-value window is really a proxy for, why the buffer owns part of the measured enthalpy, how cell and syringe concentration errors propagate differently, and how compensation gets manufactured.
Read moreA peptide identification is not an observation. It is the best-scoring candidate among the sequences the search was permitted to consider. What the digest commits you to, why CID and ETD give different ladders, what a target-decoy false discovery rate estimates, and which denominator it uses.
Read moreA dilution series is a chain of multiplications, so a 2% short transfer repeated six times is not a 2% error but an 11.5% one. Systematic versus random error, how each propagates, what gravimetric and photometric verification actually establish, and how a small tip error becomes a large potency error.
Read moreA p-value is not the probability a result is real, an n of 3 is not a sample size, and a correction chosen after seeing the data is not a correction. What a p-value measures, why n = 3 needs a three-standard-deviation effect for 80% power, what counts as an independent replicate, and how the corrections differ.
Read moreA buffer is a reagent in large molar excess, not a background condition. What the pKa on the bottle omits, how fast capacity falls away from it, why 50 mM phosphate carries 2.2 times its nominal ionic strength, which buffers bind metals or make peroxide, and the ionization enthalpy calorimetry cannot ignore.
Read moreMTT, ATP luminescence, LDH release and live/dead staining each measure a different physical quantity, and none of them measures viability. What each format is sensitive to, the two classes of tetrazolium artifact, the peptide-specific formazan trafficking confound, and why a viability drop is not a mechanism.
Read moreVehicle, scrambled sequence, inactive analog, receptor-null cells, positive reference agonist: each closes off one specific alternative explanation and is silent about the rest. This guide states, for every control in the standard set, the artifact it excludes and the artifact it leaves entirely untouched.
Read moreA fluorescent label is a second molecule bolted to the first, carrying its own charge, mass and photochemistry. FITC, TAMRA and cyanine chemistries, how an attachment site is chosen, what quenching and photobleaching remove, and the case where moving the label changed the answer by up to two orders of magnitude.
Read moreAn apparent permeability is a flux divided by a concentration that was assumed, across an area that was nominal, through a barrier the laboratory built. What Caco-2 and PAMPA each represent, how Papp and efflux ratios are computed, which controls decide whether a plate is reportable, and where extrapolation stops.
Read moreA docking score is a pose-selection statistic reported in energy-like units, not an affinity. Why peptide flexibility breaks small-molecule docking assumptions, what the published protein-peptide benchmarks actually report, how pose quality is measured, and what it takes to validate a prediction.
Read moreSome sequences fail during chain assembly for conformational rather than chemical reasons: chains hydrogen-bond into beta-sheets on the resin and bury the amine that needs acylating. How that starts, what pseudoprolines and backbone protection actually do about it, and why it surfaces as deletion peptides.
Read morePeptides partition onto glass, polypropylene and polystyrene, and the reported losses are worst at low concentration in small volumes. What the surface chemistry is, which sequences are worst affected, what the measured losses are, and what carrier proteins and low-bind plastics actually fix.
Read moreA sequence is a string of letters, but every number attached to it depends on a convention the string does not carry. Canonical sequences and isoforms, the precursor-versus-mature offset that silently shifts residue positions, why short queries defeat default search settings, and how to read a percent identity.
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