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Abstract
BackgroundBiomphalaria snails are the intermediate host of the blood fluke Schistosoma mansoni, which infect more than 67 million people in tropical areas. Phenoloxidase enzymes (POs), including tyrosinases, catecholases, and laccases, are known to play a role in the immune defenses of arthropods, but the PO activity present in Biomphalaria spp. hemolymph has not been characterized. This study was designed to characterize substrate specificity and reaction optima of PO activity in Biomphalaria spp. hemolymph as a starting point to understand the role of this important invertebrate enzyme activity in snail biology and snail-schistosome interactions.MethodsWe used spectrophotometric assays with 3 specific substrates (L-tyrosine for tyrosinase, L-DOPA for catecholase, and PPD for laccase) and diethylthiocarbarmate (DETC) as specific PO inhibitor to characterize PO activity in the hemolymph of uninfected snails from two Biomphalaria species, and to determine the impact of the parasite Schistosoma mansoni on the PO activity of its B. glabrata vector.ResultsWe identified laccase activity in hemolymph from uninfected B. glabrata and B. alexandrina. For both species, the activity was optimal at 45 °C and pH 8.5, and located in the plasma. The Km and Vmax of PO enzymes are 1.45 mM and 0.024 OD.min-1 for B. glabrata, and 1.19 mM and 0.025 OD.min-1 for B. alexandrina. When the snail vector is parasitized by S. mansoni, we observed a sharp reduction in laccase activity seven weeks after snail infection.ConclusionsWe employed a highly specific spectrophotometric assay using PPD substrate which allows accurate measurement of laccase activity in Biomphalaria spp. hemolymph. We also demonstrated a strong impact of the parasite S. mansoni on laccase activity in the snail host.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1319-6) contains supplementary material, which is available to authorized users.
Highlights
Biomphalaria snails are the intermediate host of the blood fluke Schistosoma mansoni, which infect more than 67 million people in tropical areas
Laccase activity characterized in the hemolymph of Biomphalaria spp
We found the strongest phenoloxidase (PO) activity in the hemolymph of both B. glabrata and B. alexandrina 4 h after adding the pphenylenediamine (PPD) substrate, which is the specific substrate of laccase enzymes (Fig. 1)
Summary
Biomphalaria snails are the intermediate host of the blood fluke Schistosoma mansoni, which infect more than 67 million people in tropical areas. Aquatic snails of the Biomphalaria genus are the intermediate hosts of the blood fluke Schistosoma mansoni [1, 2], trematodes that infect 67 million people in Africa and South America [3,4,5]. Many snail humoral factors have been carefully characterized in the Biomphalaria genus to identify the resistance mechanisms to schistosome infection. No clear characterization of the phenoloxidase (PO) activity of the Biomphalaria snail hemolymph was attempted. This is surprising because PO activity is considered to be an important component of
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