Prophenoloxidase

Prophenoloxidase (proPO) is a modified form of the complement response found in some invertebrates, including insects, crabs and worms.^[1] It is a copper-containing metalloprotein.^[2]

Prophenoloxidase b hexamer, Marsupenaeus japonicus.

A major innate defense system in invertebrates is the melanization of pathogens and damaged tissues. This important process is controlled by the enzyme phenoloxidase (PO).^[3] The conversion of prophenoloxidase to the active form of the enzyme can be brought about by minuscule amounts of molecules such as lipopolysaccharide, peptidoglycan and beta-1,3-glucans from microorganisms.^[4]

However, it still has many arguments in the innate immune function, especially in model invertebrate animal.^[5] The proPO homologous-protein in mammal also does not have any immune activity. Thus, it might be difficult to conclude its function in immunity.