4 – PHENOLOXIDASES IN INSECT IMMUNITY

摘要: Phenoloxidases are present as zymogens in insect hemolymph, and they become activated upon wounding or infection part of the innate immune response. These enzymes similar to mammalian tyrosinases their ability use reactive sites containing copper atoms catalyze two types reactions that require molecular oxygen a substrate. They can hydroxylate tyrosine form dihydroxyphenylalanine, oxidize o -diphenols quinones. The quinones undergo additional leading synthesis melanin, which is deposited on surface encapsulated parasites, hemocyte nodules, wound sites. melanin itself chemical species produced during appear help kill invading pathogens parasites. Rather than having sequence similarity tyrosinases, prophenoloxidases (proPOs) homologous with arthropod hemocyanins hexamerin storage proteins. ProPOs synthesized primarily by hemocytes released into plasma cell lysis. proteolytic cleavage at specific site near amino-terminus through action hemolymph serine proteases amino-terminal clip domains. proPO activating themselves protease cascade stimulated recognition microbial infection. At least some cases, activation also requires participation homolog (SPH) cofactors, lack activity. regulated inhibitors, including members serpin superfamily, active phenoloxidase (PO) may be directly inhibited proteinaceous factors. Such regulation essential because products PO activity potentially toxic host. Further research required gain more detailed understanding level assembly protein complexes deposition foreign surfaces these processes.