title: Localization and characterization of hemoglobin-degrading aspartic proteinases from the malarial parasite Plasmodium falciparum.
abstract: Three hemoglobin-degrading proteinases were partially purified from food vacuoles isolated from trophozoite-stage forms of the malarial parasite Plasmodium falciparum. Two of the proteinases (M1 and M2) were solubilized by repeated sonication. The remaining proteinase (M3) was solubilized by treatment of the particulate fraction with taurocholic acid, suggesting that proteinase M3 is a membrane-bound proteinase whereas proteinases M1 and M2 are weakly associated with parasite membrane. The location of these proteinases suggests that they may participate in the digestion of host cytosolic protein. After partial purification, but not before, proteinases M1, M2 and M3 are highly sensitive to pepstatin, supporting their designation as aspartic proteinases. These aspartic proteinases show broad specificity for protein substrates. Native hemoglobin, acid denatured hemoglobin and oxidatively damaged hemoglobin are comparable substrates. Hemoglobin within the food vacuole was shown to be primarily native hemoglobin. Chemical modification studies indicate that these three aspartic proteinases have similar properties. The peptide maps from degradation of hemoglobin, however, suggest that aspartic proteinases M1, M2 and M3 are distinct proteinases.
authors.affiliation: Department of Biochemistry, University of New Mexico School of Medicine, Albuquerque 87131.
authors.forename: D L
authors.initials: DL
authors.lastname: vander Jagt
authors.forename: L A
authors.initials: LA
authors.lastname: Hunsaker
authors.forename: N M
authors.initials: NM
authors.lastname: Campos
authors.forename: J V
authors.initials: JV
authors.lastname: Scaletti
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D002614:Chelating Agents; D004912:Erythrocytes / Q000469:parasitology; D006418:Heme / Q000031:analogs & derivatives; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008670:Metals; D010436:Pepstatins / Q000494:pharmacology; D010963:Plasmodium falciparum / Q000201:enzymology*; D013438:Sulfhydryl Compounds
chemical_list: D000962:Antimalarials; D002614:Chelating Agents; D006454:Hemoglobins; D008670:Metals; D010436:Pepstatins; D013438:Sulfhydryl Compounds; C014195:Streptomyces pepsin inhibitor; D006418:Heme; D016282:Aspartic Acid Endopeptidases; C031375:pepstatin