Figure 1: The process and the effects of citrullination. Watermelon (Citrullus lanatus L.) contains abundant arginine and citrulline as free amino acids. A) Peptidylarginine deiminase (PAD) enzymes convert peptidylarginine to peptidylcitrulline in a process called citrullination. The difference between arginine and citrulline is depicted in the red circles. B) The effects of PAD-catalysed citrullination. Loss of ionic interactions due to citrullination may destabilize intra- and intermolecular interactions, leading to the disruption of protein complexes and/or protein unfolding.