A peptide experiment almost never measures an absolute quantity. It measures a difference between your peptide and something else, and the something else determines what the result means. Reviewers know this, which is why "what was your control peptide?" is among the first questions asked of any peptide paper.
| Control | What it is | What it rules out |
|---|---|---|
| Scrambled | Same residues, different order | That the effect comes from amino acid composition, net charge or hydrophobicity rather than from the sequence |
| Alanine-substituted | One residue replaced by alanine | Identifies which individual side chains carry the effect, by removing them one at a time |
| Truncated | Shortened from one or both ends | Shows how much the flanking residues contributed, and defines the minimum active sequence |
| Unrelated peptide | Different sequence, similar length and charge | Non-specific effects of adding any peptide at that concentration |
| Phospho / non-phospho pair | Identical sequences differing only in the modification | That an antibody or binding partner is reading the modification rather than the surrounding sequence |
| D-amino acid version | Same sequence, inverted stereochemistry | Stereospecific recognition, as opposed to a surface or charge effect |
| Label-only control | The fluorophore, biotin or tag without the peptide | That the label itself is responsible for binding, uptake or signal |
| Vehicle | Buffer with the same DMSO or carrier | Solvent effects, which at the few percent DMSO common for hydrophobic peptides are not negligible3 |
A scrambled control is only informative if it is inactive in the assay, and an active scramble is a result to investigate rather than discard. Randomly reordering a short sequence can recreate a recognizable motif by chance, preserve a charge cluster that was doing the work, or produce something far less soluble than the original. Three habits avoid this: generate several scrambles and inspect them rather than taking the first; keep the termini fixed if the original had a free or capped terminus that matters; and check the scramble does not reconstruct a known motif. For very short peptides, scrambling has so few degrees of freedom that an unrelated peptide of matched length and charge is often the better control.
Controls sometimes surprise you. In the study that introduced alanine scanning, 62 single alanine substitutions across human growth hormone revealed about a dozen side chains whose replacement cost more than fourfold in receptor affinity — and one, Glu174, whose replacement increased affinity by more than fourfold.1 A control designed to lose activity gained it. That result would have been invisible without the full set.
A control peptide differs from the test peptide in exactly one respect, in principle. In practice it is easy to introduce three or four differences without noticing:
More than one, but rarely all of them. A practical minimum for most binding or activity work is a scrambled peptide and a vehicle control. Add an alanine series when you want to know which residues matter rather than merely that the sequence matters. Add a matched modification pair whenever a post-translational modification is part of the claim. Add a label-only control whenever the peptide carries a fluorophore, biotin or a cell-penetrating tag, because each of those has its own biology.
The honest test is to ask which alternative explanation a sceptical reader would raise first, and then order the peptide that eliminates it.
Please email your project details to sales@lifetein.com or use our online quotation form. Control sets are ordinary work for us, made alongside the test peptide at matched purity and counter-ion so the comparison holds.
Sequences supplied by customers are treated as confidential and are never disclosed or reused.
All LifeTein peptides are supplied for laboratory research use only. They are not for human or veterinary use, and not for diagnostic or therapeutic use.