Deamidation

Deamidation is a silent yet dangerous chemical degradation pathway that converts asparagine (Asn) and glutamine (Gln) residues into aspartic/isoaspartic acid (Asp/isoAsp) and glutamic acid (Glu), with loss of an amine (-NH₂) replaced by a hydroxyl (-OH). This reaction introduces a negative charge where none existed, shifts the peptide's isoelectric point and often alters its biological activity.

The mechanism proceeds through a cyclic succinimide intermediate which subsequently opens to yield predominantly the isoAsp isomer (70%) and the standard Asp (30%). This ratio depends on pH, temperature, neighboring sequence (a Gly at position n+1 accelerates the reaction) and the peptide's three-dimensional structure.

Accelerating factors are well characterized: alkaline pH (> 7.5) multiplies rates 10- to 100-fold, high temperatures (37 °C vs 4 °C), protic solvents, trace metal ions. Conversely, slightly acidic pH (5-6), low temperatures (≤ -20 °C for storage) and lyophilization dramatically slow kinetics.

Detection relies on LC-MS (+1 Da mass shift per deamidation event) or HPLC with isoform resolution on optimized columns. Forced stability studies (40 °C, pH 8, 4 weeks) predict sequence susceptibility.

In practical catalog terms, Asn-Gly, Asn-Ser and Asn-His sequences are most exposed. Semaglutide, liraglutide, TB-500 and many bioactive peptides contain Asn/Gln residues and must be stored lyophilized at -20 °C or -80 °C. Reconstitute only at time of use, avoid alkaline phosphate buffers, work at pH 5-6 when solubility allows: these simple rules preserve chemical integrity throughout the protocol.