Characterization of a plasminogen activator produced by Acanthamoeba castellanii

Mol Biochem Parasitol. 1995 Jul;73(1-2):157-64. doi: 10.1016/0166-6851(94)00109-z.


Serine proteases play an important role in a diverse array of biological processes, including embryogenesis, metastasis, angiogenesis, thrombolysis and tissue invasion by certain parasites. The latter observation prompted us to explore the possibility that the tissue-invasive ocular parasite Acanthamoeba castellanii elaborates one or more serine proteases. Acanthamoeba sp. are pathogenic free-living amoebae that can produce an invasive, blinding inflammatory disease of the cornea, termed Acanthamoeba keratitis. The present study reports the preliminary purification and characterization of a novel plasminogen activator from an ocular isolate of A. castellanii. The parasite-derived enzyme has a molecular mass of approx. 40 kDa and produces a single band of lysis on fibrinogen-agarose zymographs. Activity of the enzyme is completely inhibited by treatment with diisopropylfluorophosphate, indicating that it is a serine protease. The parasite-derived serine protease is not inhibited by amiloride which is a strong inhibitor of urokinase-type plasminogen activator. Additionally, the enzyme is not inhibited by plasminogen activator inhibitor-1 which is the primary physiological inhibitor of both urokinase and tissue-type plasminogen activator. It does not cross-react with antibodies specific for human urokinase or tissue-type plasminogen activator. The parasite-derived enzyme activates plasminogen from several mammalian species, including human, cow and pig. Thus, it is possible that this parasite-derived serine protease contributes to the pathogenesis of Acanthamoeba keratitis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acanthamoeba / enzymology*
  • Acanthamoeba / isolation & purification
  • Acanthamoeba / pathogenicity
  • Acanthamoeba Keratitis / parasitology
  • Amiloride / pharmacology
  • Animals
  • Cattle
  • Cross Reactions
  • Humans
  • Isoflurophate / pharmacology
  • Molecular Weight
  • Plasminogen Activator Inhibitor 1 / pharmacology
  • Plasminogen Activators / immunology
  • Plasminogen Activators / isolation & purification*
  • Plasminogen Activators / metabolism
  • Plasminogen Inactivators / pharmacology
  • Serine Proteinase Inhibitors / pharmacology


  • Plasminogen Activator Inhibitor 1
  • Plasminogen Inactivators
  • Serine Proteinase Inhibitors
  • Isoflurophate
  • Amiloride
  • Plasminogen Activators