PADI4 citrullination activity was analysed using the COLDER assay 52 in 96-well plates. Peptide dilutions were prepared from a 500 µM stock, to give a 10 times concentrated dilution series (500 µM, 300 µM, 100 µM, 30 µM, 10 µM, 3 µM, 1 µM, 0. Samples were incubated for 20 min at 95 °C before measuring absorbance at 540 nm on a CLARIOstar Plus (BMG LABTECH). Data analysis was performed with GraphPad Prism. Data are presented as the average ± standard error of the mean from at least two independent replicates.