Isolation of an Entamoeba histolytica intracellular alkaline phospholipase A₂

Abstract

The major hemolytic activity of Entamoeba histolytica is located in a subcellular fraction called P30. Its maximal effect is observed at pH 8.0 and 1 mM Ca²⁺ and is due to a phospholipase A (PLA). In the present study a membrane-associated phospholipase A₂ was purified from P30 to homogeneity. P30 was fractionated with ethyl ether and the insoluble fraction was extracted with 1 M KCl. The KCl-soluble material was diluted ten times with 0.1 M TRIS-HCl (pH 9.5) and passed through a chromatofocusing column with a 9–4 pH gradient. Four peaks with PLA₂ activity were obtained. By affinity chromatography, peak II, the one with the highest specific activity, was resolved in three more PLA₂ peaks. Peak II.2 had the highest PLA₂ specific activity. When analyzed by sodium dodecyl sulfate-polyacrylamide slab-gel electrophoresis under nonreducing conditions, peak II.2 yielded a single band with an apparent molecular mass of 30 kDa. Under reducing conditions the protein dissociated into two 15-kDa monomers. The purified PLA II.2 displayed its activity at the same conditions under which the P30 hemolytic activity was maximal. The isoelectric point of PLA II.2 was 7.0. The purification procedure described above provides sufficient material for determination of the relative importance of the enzyme in the E. histolytica pathogenic mechanisms.