- Document
- ST-04
- Section
- Storage fundamentals
- Revised
- Sources checked
- Bands
- −20 °C2–8 °C
Light Exposure: Which Peptides Need Protecting and How
Ultraviolet and short-wavelength visible light can oxidize aromatic and sulfur-containing residues. How to tell whether a peptide is at risk, and what amber glass and opaque boxes actually do.
Bench card
- Trp, Tyr, Phe, His, Met and Cys are the residues most involved in light-driven degradation.
- UV is the main concern, but visible light can drive photosensitized oxidation, especially with trace impurities present.
- Amber glass blocks most UV and short-wavelength visible light; an opaque secondary box blocks nearly all of it.
- Solutions are more vulnerable than dry powder.
- Keep bench exposure brief, and avoid leaving vials near windows or under bright task lamps.
“Protect from light” appears on many peptide datasheets. Sometimes it reflects measured photosensitivity; often it is a sensible precaution. This guide explains the mechanism so you can decide how seriously to take it for a given sequence.
How light damages peptides
Light only causes chemistry if something absorbs it. In peptides the main absorbers are the aromatic residues: tryptophan absorbs strongly around 280 nm, tyrosine slightly lower, and phenylalanine weakly. Absorbed energy can break bonds directly or, more commonly, generate reactive oxygen species such as singlet oxygen. These then oxidize nearby residues, including methionine, histidine and cysteine, which do not absorb much light themselves.
Kerwin and Remmele’s review of photodegradation in protein products describes both routes and notes that trace impurities, metal ions and excipients can act as photosensitizers. That means a peptide with no aromatic residues is not automatically light-safe.
Which sequences are most at risk
- Peptides containing tryptophan, which is both a strong UV absorber and easily oxidized.
- Peptides with methionine, cysteine or histidine, which are vulnerable to photosensitized oxidation.
- Metal complexes such as copper peptides, where light can affect the metal centre.
- Any peptide in solution, where reactive species diffuse freely.
What containers do
| Container | Light protection | Notes |
|---|---|---|
| Clear borosilicate glass | Passes most UVA and visible light | Blocks short-wave UVC and much UVB |
| Amber glass | Absorbs most UV and blue light | Light transmission is a pharmacopeial test (USP <671>) |
| Clear polypropylene tube | Little protection | Use inside an opaque box |
| Amber or opaque tube | Good | Check that labels remain readable |
| Opaque secondary box or foil | Near total | Simple and effective for freezer storage |
Practical precautions
- Store vials in a closed, opaque box inside the freezer or refrigerator.
- Use amber vials or tubes for solutions of light-sensitive peptides, or wrap clear tubes in foil.
- Keep bench time short and away from windows. Standard room lighting for a few minutes is rarely a problem; hours under a bright lamp may be.
- Note any colour change. A yellowing solution of a Trp-containing peptide is a warning sign.
References
- Kerwin BA, Remmele RL Jr. Protect from light: photodegradation and protein biologics. J Pharm Sci. 2007;96(6):1468–1479. DOI
- ICH Q1B. Stability Testing: Photostability Testing of New Drug Substances and Products. International Council for Harmonisation, 1996. ICH
- Li S, Schöneich C, Borchardt RT. Chemical instability of protein pharmaceuticals: mechanisms of oxidation and strategies for stabilization. Biotechnol Bioeng. 1995;48(5):490–500. DOI
- USP General Chapters <660> Containers—Glass and <671> Containers—Performance Testing (including light transmission). United States Pharmacopeia.