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Glutamate–cysteine ligase (GCL) is a heterodimer enzyme composed of a catalytic subunit (GCLC) and a modifier subunit (GCLM). This enzyme catalyses the synthesis of γ-glutamylcysteine, a precursor of glutathione. cDNAs of the putative glutamate–cysteine ligase catalytic ( Ace -GCLC) and modifier subunits ( Ace -GCLM) of Ancylostoma ceylanicum were cloned using the RACE-PCR amplification method. The Ace-gclc and Ace - gclm cDNAs encode proteins with 655 and 254 amino acids and calculated molecular masses of 74.76 and 28.51 kDa, respectively. The Ace -GCLC amino acid sequence shares about 70% identity and 80% sequence similarity with orthologs in Loa loa , Onchocerca volvulus , Brugia malayi , and Ascaris suum , whereas the Ace -GCLM amino acid sequence has only about 30% sequence identity and 50% similarity to homologous proteins in those species. Real-time PCR analysis of mRNA expression in L3, serum stimulated L3 and adult stages of A. ceylanicum showed the highest level of Ace -GCLC and Ace -GCLM expression occurred in adult worms. No differences were detected among adult hookworms harvested 21 and 35 dpi indicating expression of Ace-gclc and Ace-gclm in adult worms is constant during the course of infection. Positive interaction between two subunits of glutamate–cysteine ligase was detected using the yeast two-hybrid system, and by specific enzymatic reaction. Ace -GCL is an intracellular enzyme and is not exposed to the host immune system. Thus, as expected, we did not detect IgG antibodies against Ace -GCLC or Ace -GCLM on days 21, 60 and 120 of A. ceylanicum infection in hamsters. Furthermore, vaccination with one or both antigens did not reduce worm burdens, and resulted in no improvement of clinical parameters (hematocrit and hemoglobin) of infected hamsters. Therefore, due to the significant role of the enzyme in parasite metabolism, our analyses raises hope for the development of a successful new drug against ancylostomiasis based on the specific GCL inhibitor. [ABSTRACT FROM AUTHOR]