Protein pattern and activity staining of PPO from Pacific white shrimp (a) and PPO activity as affected by proteases from hepatopancreas (b). M: Molecularweight markers; CBB: gel stained with Coomassie Brilliant Blue; L-DOPA: gel stained with 15 mM L-DOPA in sodium phosphate buffer (pH 6.0). CE: Crude extracts of cephalothorax; CA: crude extracts of carapace; CA + P: crude extracts of carapace mixed with proteases from hepatopancreas (1:1).