Although several potent covalent inhibitors had been found, we decided to test whether we could further optimise the selection conditions with the hope of promoting greater discrimination between more and less potent inhibitors. To this end, we repeated the selection starting from round 2, reducing incubation of peptides with PADI4 to only 15 minutes at 0 °C. As we expected, we saw a reduction in positive library recovery which matched the increased stringency, but recovery still increased round-by-round (Figure ).