Activity of intracellular phospholipase A1 and A2 in Giardia Lamblia

Neither phospholipase A(1) (PLA A(1))or phospholipase A(2) (PLA A(2)), nor their respective genes, have been identified in Giardia lamblia, even though they are essential for lipid metabolism in this parasite. A method to identify, isolate, and characterize these enzymes is needed. The activities of PLA A(1) and PLA A(2) were analyzed in a total extract (TE) and in vesicular (P30) and soluble (S30) subcellular fractions of G. lamblia trophozoites; the effects of several chemical and physicochemical factors on their activities were investigated. The assays were performed using substrate labeled with C-14, and the mass of the C-14-product was quantified. PLA A(1) and PLA A(2) activity was present in the TE and the P30 and S30 fractions, and it was dependent on pH and the concentrations of protein and Ca2+. In all trophozoite preparations, PLA A(1) and PLA A(2) activities were inhibited by ethylenediaminetetraacetic acid and Rosenthal's inhibitor. These results suggest that G. lamblia possesses several PLA A(1) and PLA A(2) isoforms that may be soluble or associated with membranes. In addition to participating in G. lamblia phospholipid metabolism, PLA A(1)and PLA A(2) could play important roles in the cytopathogenicity of this parasite.