Research and Target Peptides

Research & Target Peptides — Frequently Asked Questions

Research peptides are intended for in-vitro assays, screening, biophysics, and animal-model use under laboratory standards. Therapeutic / pharmaceutical peptides are made under ICH Q7 for human dosing with full impurity profiling. Sequence can be identical; the dividing line is QA, documentation, and intended use, not the chemistry.

N-terminal labeling is simplest and suits C-terminal-active ligands. C-terminal labeling (lysine side chain via NHS ester, cysteine via maleimide) is used when the N-terminus is part of the binding interface. We model both options against your SAR data and recommend the placement with the smallest activity shift.

Short aliphatic spacers (Ahx, β-Ala, Mini-PEG) keep fluorophores / biotin close to the peptide and minimize steric clash. Longer PEG linkers (PEG2–PEG4) are preferred for fluorescence polarization and SPR where the label must rotate freely. Hydrophobic linkers can cause non-specific binding; choose PEG for aqueous assays.

(1) Labeling a residue inside the binding pocket destroys affinity — always run a labeled vs unlabeled Kd comparison; (2) dye aggregation causes false quenching artifacts, use BSA / DMSO controls; (3) free dye contamination distorts FRET and FP assays; (4) D-amino-acid contamination in supposedly pure L-peptide changes bioactivity.

For affinity mapping: alanine scan (10–15 analogs). For protease stability: D-amino-acid or N-methyl scan at P1′/P2′ positions. For pharmacophore: truncation series from each terminus. Combining positional truncation + targeted substitution in one campaign typically converges on a minimal active motif in 30–50 analogs.

Yes. FRET pairs (FAM/TAMRA, Cy3/Cy5, Alexa 488/546) are built by orthogonal side-chain protection schemes. Triple labels combining biotin + fluorophore + isotope, or fluorophore + quencher + affinity tag, support parallel pull-down / imaging / MS workflows in one construct. We design to your detection platform.