Identifying Peptide Degradation

Why Peptides Degrade

Peptides are chains of amino acids held together by peptide bonds. These bonds are stable under ideal conditions but can break down due to:

• Hydrolysis — water molecules attack peptide bonds, especially at elevated temperatures
• Oxidation — oxygen reacts with certain amino acids (methionine, cysteine, tryptophan)
• Aggregation — peptides clump together, forming visible precipitates
• Deamidation — asparagine and glutamine residues convert to aspartic and glutamic acid
• Microbial contamination — bacteria produce enzymes that digest peptides

Visual Indicators of Degradation

In Lyophilized (Powder) Form

• Color change — fresh peptide should be white or off-white; yellowing suggests oxidation
• Texture change — should be fluffy cake; sticky or clumped powder indicates moisture exposure
• Shrinking away from vial walls — can indicate temperature cycling

In Reconstituted Solution

• Cloudiness or turbidity — fresh solution should be crystal clear
• Visible particles — floating specks or sediment indicate aggregation
• Color change — any yellow, brown, or pink tint suggests degradation
• Gel formation — thick, gel-like consistency is a sign of severe aggregation

Non-Visual Indicators

Some degradation cannot be seen with the naked eye:

• Reduced research activity — expected results not achieved at normal concentrations
• Unusual odor — bacterial contamination can produce sulfurous or foul smells
• Changed pH — degradation products can shift solution pH

Prevention Strategies

• Store lyophilized peptides at -20°C or colder
• Minimize freeze-thaw cycles — create single-use aliquots if needed
• Use bacteriostatic water for multi-use reconstitution
• Keep reconstituted solutions refrigerated (2-8°C)
• Protect from light — wrap vials in foil if storing long-term
• Use sterile technique — always swab stoppers, use fresh needles