Proteolytic Activation of Prophenoloxidase in an Insect Manduca Sexta
Phenol oxidase (PO) (EC18.104.22.168) is important in cuticular sclerotization and in defense against pathogens and parasites (Söderhäll et al., 1996; Sugumaran, 1996; Ashida and Brey, 1998). PO catalyzes hydroxylation of monophenols to o-diphenols and oxidation of o-diphenols to quinones. The quinones take part in sclerotization of cuticle and serve as precursors for synthesis of melanin. PO is synthesized in arthropods as an inactive zymogen, prophenoloxidase (proPO), which can be activated by proteolytic cleavage at a specific site in the protein. Wounding of an insect or exposure to certain microbial polysaccharides leads to the activation of a proteinase that specifically activates proPO, perhaps at the last step of a proteinase cascade (Ashida and Brey, 1998). The reactions catalyzed by PO then can result in melanization of foreign organisms trapped in capsules or hemocyte nodules (Gillespie et al., 1997).
KeywordsHorseshoe Crab Phenol Oxidase Amidase Activity Phenol Oxidase Activity Microbial Polysaccharide
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