Figure 1. Principle of chemical modification and detection of citrulline-containing proteins.

Peptidylcitrullines are chemically modified with antipyrine and 2,3-butanedione at low pH, followed by dialysis against a buffer with neutral pH (Panel A) and chemically modified citrullinated proteins are detected by sandwich ELISA (Panel B). Coating antibodies are specific for the protein of interest and antibodies against modified citrulline residues and peroxidase labelled anti-rabbit antibodies are used for detection. Chemically modified citrulline (Cit) is marked with an asterisk.