title: The acid phosphatase positive organelles of the Giardia lamblia trophozoite contain a membrane bound cathepsin C activity.
abstract: We found a dipeptidyl aminopeptidase activity in the parasitic protozoan Giardia lamblia with properties similar to the lysosomal cathepsin C of rat-liver lysosomes. Subcellular fractionation of this parasite indicated that the cathepsin C activity is located in organelles not distinguishable from the ones containing acid phosphatase, a known marker enzyme of Giardia lysosome-like peripheral vesicles. Contrary to the rat lysosomal enzyme, Giardia cathepsin C behaved like a membrane protein. Moreover, the enzyme was not solubilized by Triton X-100 or Triton X-100/SDS at 0 degrees C but could be substantially solubilized by octylglucoside, Triton X-100 at 37 degrees C or by a pretreatment with the cholesterol complexing agent beta-cyclodextrin before the Triton/SDS treatment carried out at 0 degrees C. These observations suggest that binding/anchorage of this enzyme to membranes occurs in cholesterol-rich microdomains.
authors.affiliation: Department of Physiological Chemistry, University of Namur (FUNDP), 61, rue de Bruxelles, B-5000, Namur, Belgium.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Thirion
authors.forename: Robert
authors.initials: R
authors.lastname: Wattiaux
authors.forename: Michel
authors.initials: M
authors.lastname: Jadot
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis*; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D020789:Cathepsin C / Q000032:analysis / Q000378:metabolism*; D002784:Cholesterol; D003505:Cyclodextrins; D016829:Giardia lamblia / Q000648:ultrastructure*; D008247:Lysosomes / Q000737:chemistry / Q000201:enzymology; D021962:Membrane Microdomains / Q000737:chemistry; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism*; D017830:Octoxynol; D015388:Organelles / Q000737:chemistry* / Q000201:enzymology; D013347:Subcellular Fractions / Q000737:chemistry
chemical_list: D015415:Biomarkers; D003505:Cyclodextrins; D008565:Membrane Proteins; D017830:Octoxynol; D002784:Cholesterol; D000135:Acid Phosphatase; D020789:Cathepsin C