Purification and characterization of two glutathione peroxidases from embryo of the camel tick Hyalomma dromedarii

Two glutathione peroxidase isoenzymes were purified from 24-day old embryos of the camel tick Hyalomma dromedarii and designated tick embryo glutathione peroxidase 1 and 2 (TEGPx1 and TEGPx2). The purification procedure involved ammonium sulfate precipitation, as well as ion exchange and gel filtration column chromatography. Glutathione peroxidase isoenzymes subunit molecular mass was determined by SDS-PAGE to be 36 ± 2 kDa and 59 ± 1.5 kDa for TEGPx1 and TEGPx2, respectively. TEGPx1 isoenzyme exhibited a dimeric structure with native molecular mass of 72 kDa while TEGPx2 was a monomeric protein. TEGPx1 and TEGPx2 displayed their pH optima at 7.6 and 8.2. Both isoenzymes cleaved preferentially H2O2 with K m values of 24 and 49 μM. Iodoacetamide competitively inhibited TEGPx1 with K i value of 0.45 mM and 1.10; phenanthroline competitively inhibited TEGPx2 with K i value of 0.12 mM. These results indicate the presence of two different forms of glutathione peroxidase in the developing camel tick embryos. This finding enhances our knowledge and understanding of the physiology of these ectoparasites and will encourage the development of new and untraditional control methods.