Characterization and partial purification of a leucine aminopeptidase from Fasciola hepatica

An aminopeptidase activity capable of hydrolyzing different aminomethylcoumarin amino acids, but mainly leucine-7-amino-4-methylcoumarin (Leu-NHMc), was detected in deoxycholic soluble extracts from adult Fasciola hepatica. The enzyme (EC 3.4.11.1) was partially purified by gel filtration and EAH-Sepharose affinity chromatography using bestatin as a ligand. Results obtained by gel filtration, direct fluorogenic substrate analysis in polyacrylamide gel, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggest that in a native form the enzyme might be aggregated as a high molecular weight complex. By affinity chromatography on concanavalin A Sepharose, the enzyme did not bond to the column showing that it lacks mannose residues. The F. hepatica aminopeptidase was characterized as a metalloproteinase based on its activation by Mn2+ and Mg2+, and its inhibition by EDTA, 1,10-phenanthroline, and bestatin. It has an optimal activity at a pH between 8.0 and 8.5. Histochemical localization revealed strong leucine naphthylamidase activity at the cells lining the gut epithelium of the parasite.