A peptide is an amino acid sequence that can form disulfide bonds with itself or with other proteins, resulting in a protein dimer, multimer or complex. It is also a chemical modification that can be introduced into the target protein through the formation of a bond between its thiol and cysteine groups. Chemicals that form such a bond with the thiol group of a cysteine peptide residue can cause the target protein to change its structure, which can in turn lead to a disruption in its function or to the formation of toxic oxidative intermediates.

The in chemico direct peptide reactivity assay (DPRA) and its kinetic variant, the kinetic direct peptide reactivity assay, are used to assess whether chemicals can form stable adducts with a model cysteine-containing peptide under certain conditions. These adducts are quantified using a fluorescence readout. The DPRA and kDPRA data matrix is analysed to give a reactivity parameter logkmax, which can be used to classify chemicals into the 1A potency class, corresponding to an EC3 value of 2% in the mouse local lymph node assay (LLNA).

However, the DPRA/kDPRA method does not always work well, particularly with acyl transfer agents that do not give stable adducts with the model peptide under the DPRA/kDPRA test conditions. In addition, the results obtained by the DPRA/kDPRA for some chemicals that do not generate significant adducts with the peptide under the test conditions – such as chlorpromazine and glutaraldehyde – do not always correlate well with in vivo LLNA and human sensitization data.peptides for sale