Purification and characterization of phenoloxidase from the hemocytes of Eurygaster integriceps (Hemiptera: Scutelleridae)

Insects protect themselves from microbial invaders by two main immune activities, namely the cellular and humoral reactions. Phenoloxidases are oxidative enzymes that have an important role in both cell-mediated and humoral immunity. In this study, the purification and biochemical characterization of a phenoloxidase from the hemocytes of the Sunn pest Eurygaster integriceps Puton (Hemiptera: Scutelleridae) were carried out. After the final purification step, the enzyme was purified 7.31-fold with a recovery of 3.94% and a specific activity of 4.95 U/mg protein. Results of the biochemical characterization showed that the purified phenoloxidase has a maximum activity at pH 6 and at 30–35 °C and is stable for 24–36 h. Divalent cations such as Ca2+ and Cu2+ significantly increased the enzymatic activity and synthetic inhibitors such as phenylthiourea significantly decreased it. The purified phenoloxidase has a molecular mass of 22 kDa. The current paper represents a further step towards the characterization of humoral immunity of E. integriceps in order to develop new strategies for the biological control of the Sunn pest.