prophenoloxidase

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Prophenoloxidase (proPO) is a modified form of the complement response found in some invertebrates, including insects, crabs and worms.{{Cite journal|url=http://www.scs.carleton.ca/~soma/biosec/readings/sharkimmu-sciam-Nov1996.pdf |title=Immunity and the Invertebrates|journal= Scientific American|date=November 1996| pages =60–66|doi=10.1038/scientificamerican1196-60|last2=Habicht|volume=275|issue=5|last1=Beck|first1=Gregory|first2=Gail S.|pmid=8875808|bibcode=1996SciAm.275e..60B}} It is a copper-containing metalloprotein.{{Cite journal|last1=Sánchez-Aparicio|first1=José-Emilio|last2=Tiessler-Sala|first2=Laura|last3=Velasco-Carneros|first3=Lorea|last4=Roldán-Martín|first4=Lorena|last5=Sciortino|first5=Giuseppe|last6=Maréchal|first6=Jean-Didier|date=2021-01-25|title=BioMetAll: Identifying Metal-Binding Sites in Proteins from Backbone Preorganization|url=https://doi.org/10.1021/acs.jcim.0c00827|journal=Journal of Chemical Information and Modeling|volume=61|issue=1|pages=311–323|doi=10.1021/acs.jcim.0c00827|pmid=33337144 |issn=1549-9596|hdl=10261/310255|hdl-access=free|url-access=subscription}}

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).{{Cite journal|pmid=15199959|year=2004|last1=Cerenius|first1=L|last2=Söderhäll|first2=K|title=The prophenoloxidase-activating system in invertebrates|volume=198|pages=116–26|journal=Immunological Reviews|doi=10.1111/j.0105-2896.2004.00116.x|s2cid=10614298}} 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.{{Cite journal|pmid=9523106|year=1998|last1=Söderhäll|first1=K|last2=Cerenius|first2=L|title=Role of the prophenoloxidase-activating system in invertebrate immunity|volume=10|issue=1|pages=23–8|journal=Current Opinion in Immunology|doi=10.1016/S0952-7915(98)80026-5}}

However, it still has many arguments in the innate immune function, especially in model invertebrate animal.{{Cite journal|pmc=1369246|year=2006|last1=Leclerc|first1=V|last2=Reichhart|first2=JM|title=Prophenoloxidase activation is not required for survival to microbial infections in Drosophila|volume=7|issue=2|pages=231–5|journal=EMBO Rep|doi= 10.1038/sj.embor.7400592|pmid=16322759}} The proPO homologous-protein in mammal also does not have any immune activity. Thus, it might be difficult to conclude its function in immunity.