Zinc as a co-factor for an enzyme involved in exsheathment of Haemonchus contortus

Abstract

The activity of concentrated exsheathing fluid of Haemonchus contortus against isolated sheaths was not inhibited by ethylenediamine tetra-acetic acid (EDTA), 10 −2 M, even when the concentrations of Mg and Mn were < 4 × 10 −4 M and < 0·9 × 10 −6 M respectively. Purified or diluted solutions of exsheathing fluid, even in the presence of Mg 2+, 10 −3 M, were inhibited. Leucine aminopeptidase (LAP) in exsheathing fluid was active even at concentrations of Mg < 1·3 × 10 −5M. Concentrated solutions were partially inhibited by EDTA, 10 −2 M, at low concentrations of Mg; inhibition was increased in diluted and purified preparations. 1,10-phenanthroline ( Ophen) strongly inhibited exsheathing activity (Zn < 1 × 10 −6 M). When Zn 2+, 10 −3 M was added, the inhibition was abolished. The hydrolysis of l-leucinamide was greatly increased in the presence of Ophen, 10 −4 M; this effect was abolished by adding Zn 2+, 10 −3 M. It is suggested that exsheathing fluid from at least some ‘strains’ of H. contortus contains a Zn metallo-enzyme, probably LAP, which is involved in the process of exsheathment.