Each ionisable group on a peptide gains or loses protons depending on pH. That changes its net charge and, with it, its solubility: near the isoelectric point the peptide tends to precipitate or aggregate. In addition, many degradation reactions depend on pH. Deamidation is faster at neutral or alkaline pH; hydrolysis of certain bonds and aspartate isomerisation, in acidic conditions.
That is why peptide formulations usually include a buffer (acetate, citrate, phosphate, histidine) that holds pH in the range where the molecule is most stable. Finding that optimum is a central part of developing any peptide drug.
In the lab, the pH of the reconstitution solvent can be the difference between a clear solution and a cloudy one. Bacteriostatic water has a slightly acidic pH, suitable for a large share of peptides.
When a peptide does not dissolve or turns cloudy, pH is usually the first variable to check, before assuming the material is faulty.
Related terms
Learn it in depth at the Peptide University
- The lyophilized form and its diluents · Module 8
- Physical degradation: aggregation and adsorption · Module 11
- Lyophilization and excipients · Module 11
- From amino acid to peptide · Module 1
- Chemical degradation: the weak points of the sequence · Module 11
Related catalogue compounds
Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).