Phenoloxidases (POs) are innate immune proteins involved in the melanization process. POs catalyze the oxidation of phenols to quinones, which subsequently polymerize into melanin at the site of infection and around parasites. POs are synthesized as an inactive zymogen prophenoloxidase (PPO), which are cleaved to generate active POs. (Adapted from FBrf0224867 and FBrf0229770).
Notes on Group
A good summary of the role of PHENOLOXIDASES (POs) in melanin biosynthesis pathway can be found in Figure 2 of FBrf0215359.