Educational guides and overviews on research peptides, what they are and how they're studied in the laboratory. For research use only.
Most replication failures are not fraud; they are experiments that were not the experiment the methods section described. Where the discrepancies hide: reagent identity, cell line misidentification, undisclosed peptide content, pseudoreplication and low power, and the reporting that closes each gap.
Read moreSPR reports a refractive index change; every rate constant is inferred from it under a model you chose. Immobilization chemistry and orientation, ka and kd and the KD they define, mass transport limitation, regeneration, and the arithmetic that makes a small analyte hard.
Read moreTirzepatide is a 39-residue peptide engineered to activate two incretin receptors. The published pharmacology says it mimics native GIP at one and diverges sharply from GLP-1 at the other — while β-arrestin results from three different systems do not yet reconcile.
Read moreCell-associated, internalized and cytosol-accessible are three different measurements. The fixation artifact that overturned an early literature, what clathrin, caveolar and macropinocytic assignments rest on, why low-temperature and inhibitor controls are necessary but not sufficient, and the arithmetic behind them.
Read moreEvery membrane measurement made outside a cell is made in a substitute. Lipid composition and curvature, the q ratio that drifts when you dilute it, scaffold length as a size control, detergent-free polymer extraction, and what each construct throws away.
Read moreA native spectrum reports mass-to-charge, not mass, and it reports it in vacuum. What has to be preserved to get a stoichiometry, why charge reduction helps, how nonspecific binding mimics a result, and the caveat that governs the whole exercise.
Read moreSolution NMR measures frequencies and intensities, not coordinates. NOE distance bounds and their spin-diffusion bias, chemical shift indexing and its limits, why inverse-sixth-power averaging lets a minority conformation dominate a restraint, and why a bundle of models reports precision, not motion.
Read moreA plasma stability half-life is a narrower number than it looks. This guide covers matrix choice, the protease classes doing the cutting, anticoagulant and quench chemistry, half-life fitting, and why species, donor and dilution change the answer.
Read moreExopeptidases need a free terminus, endopeptidases do not — yet neprilysin still counts from the C-terminus. A guide to subsite nomenclature, the DPP-4 and neprilysin structures behind their preferences, and how cleavage sites are mapped by PICS, MSP-MS and N-terminomics.
Read moreAn internalization assay measures accessibility, not location. Surface biotinylation and antibody labeling, pH-sensitive fluorophores and the pulsed-pH protocol, separating recycling from degradation, and the dependencies hidden in any internalization percentage — starting with which quantity is the denominator.
Read moreA retention time is a hydrodynamic property, not a mass, and the calibration curve converting one to the other carries every assumption of the standards. What light scattering fixes, what it does not, how sedimentation velocity separates with no column at all, and how to tell a stable oligomer from a reversible one.
Read moreA thermal shift assay reports the temperature at which a fluorescence signal changes most steeply. Dye-based DSF versus intrinsic-fluorescence nanoDSF, what a melting temperature does and does not report, why a Tm shift is not a binding affinity, and where buffer screening holds up.
Read moreAn alanine scan returns positions and free-energy numbers, but those numbers are differences between two molecules under one set of conditions, not properties of residues. What C-beta truncation removes, how the O-ring hotspot picture was built, where additivity fails, and why deletion is a different experiment.
Read moreTwo mechanisms sit under every half-life platform: added hydrodynamic bulk and FcRn recycling. Albumin-binding fatty acids, albumin and Fc fusion, PASylation and XTEN, and glycoengineering, with what each costs in receptor affinity, valency, expression system and manufacturability.
Read moreCleavable versus non-cleavable is a statement about catabolic fate, not bond strength. What actually cleaves a valine-citrulline linker, why a mouse esterase broke a whole class of stability data, how an average drug-to-peptide ratio hides its distribution, and what a stability assay is really measuring.
Read moreA MIC is a property of a peptide in one medium, against one inoculum, in one kind of plastic. Broth microdilution and its two-fold ladder, divalent cations and salt, inoculum dependence, the hemolysis assay's moving denominator, and why a selectivity index does not survive the trip between papers.
Read moreCationic versus amphipathic classes, why cargo and fluorophore are part of the molecule, what the scrambled and D-enantiomer controls can and cannot decide, and the assays that measure cytosolic arrival rather than uptake.
Read moreA cryo-EM structure is a map inferred from noisy images, then a model inferred from that map. The single-particle workflow, why the global resolution figure is a half-set statistic, how resolution varies within one map, map-to-model fitting and scoring, and what a deposited GPCR complex actually establishes.
Read morePuromycin makes the genotype-phenotype link covalent; ribosome display holds it together with buffer conditions instead. What that difference costs, where cell-free library sizes actually come from, why fusion yield depends on flanking sequence, and which phage artifacts these formats remove.
Read moreAn overlapping scan measures one intensity per spot and nothing else. Scan arithmetic and what the offset guarantees, SPOT synthesis on cellulose, why linear peptides cannot hold a conformational epitope, what spot intensity does and does not report, and the controls that separate binding from surface chemistry.
Read moreMolar activity and radiochemical purity have different denominators, and neither converts into the other. Matching a bifunctional chelator to the radiometal, trace metals competing for the cage, radiolysis after synthesis, and the layered QC a labeled batch actually receives.
Read moreA SAR table looks like a ranking but is a set of measurements. What a fold-change column is a ratio of, why potency, affinity and efficacy can point in different directions, how far apart two correct EC50 values can sit, and what happens to a series when the readout changes.
Read moreA crystal structure is a model refined against diffraction data, and the bound peptide contributed least to it. What a resolution figure permits, why global R factors will not catch a bad peptide, what B-factors and occupancies encode, and how a peptide can be genuinely bound yet only partly supported by density.
Read moreA polarization reading reports how far a fluorophore rotated during its excited-state lifetime, and binding is only one reason that number moves. Why the tracer must be the small partner, how probe choice sets the affinity floor, why Cheng-Prusoff is the wrong conversion in competition mode, and the artefacts that shift mP without shifting occupancy.
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