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Which Peptides Can You See at 280 nm? A Tryptophan and Tyrosine Census
A UV spectrophotometer reads protein concentration at 280 nm, but this only works if the molecule contains tryptophan or tyrosine. Many short peptides contain neither, which surprises people the first time a reading comes back blank.
The census
| Peptide | Trp | Tyr | Readable at 280 nm? |
|---|---|---|---|
| BPC-157 | 0 | 0 | No |
| KPV | 0 | 0 | No |
| Semax | 0 | 0 | No (Phe only, weak near 257 nm) |
| DSIP | 1 | 0 | Yes, weakly |
| Melanotan-2 | 1 | 0 | Yes, weakly |
| Melanotan-1 | 1 | 1 | Yes |
| Tesamorelin | 0 | 2 | Yes, weakly |
How strong is the signal?
Tryptophan absorbs at about 5,500 M⁻¹cm⁻¹ and tyrosine at about 1,490 M⁻¹cm⁻¹. A single tryptophan in a small peptide gives a modest signal, so low concentrations disappear into the noise.
The workaround
When there is no aromatic residue, labs read the peptide bond itself near 214 nm. This is more sensitive but also picks up buffers, preservatives and contamination, so clean blanks matter. HPLC detectors on a certificate of analysis are typically set to 214 nm for exactly this reason.
A practical example
If you wanted to check a solution of Melanotan-2 10mg, its tryptophan gives you a usable 280 nm signal, while a solution of BPC-157 would need the 214 nm route.
- No Trp or Tyr: use 214 nm.
- One Trp: 280 nm works at higher concentrations.
- Always measure a matching blank.
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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.