Prophenoloxidase (proPO) is a modified form of the complement response found in some invertebrates, including

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s, crabs and

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wo ...

s. It is a

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

-containing

metalloprotein Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins (out of ~20,000) contain zinc-binding protein domains al ...

. A major innate defense system in invertebrates is the melanization of pathogens and damaged tissues. This important process is controlled by the enzyme

phenoloxidase Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in Browning (food process), fruit browning, is a tetramer that contains four atoms of copper per molecule. PPO may accept monophenol , monophenols and/or ...

(PO). The conversion of prophenoloxidase to the active form of the enzyme can be brought about by minuscule amounts of molecules such as

lipopolysaccharide Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer ...

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...

and beta-1,3- glucans from

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

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

References

Insect immunity Oxidoreductases {{insect-stub