Purification and Biochemical Characterization of Digestive Lipase in Whiteleg Shrimp
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Penaeus vannamei lipase was purified from midgut gland of whiteleg shrimp. Pure lipase (E.C. 126.96.36.199) was obtained after Superdex 200 gel filtration and Resource Q anionic exchange. The pure lipase, which is a glycosylated molecule, is a monomer having a molecular mass of about 44.8 kDa, as determined by SDS-PAGE analysis. The lipase hydrolyses short and long-chain triacylglycerols and naphthol derivates at comparable rates. A specific activity of 1787 U mg−1 and 475 U mg−1 was measured with triolein and tributyrin as substrates, respectively, at pH 8.0 and 30°C in the absence of colipase. The lipase showed a Km, app of 3.22 mM and kcat, app/Km, app of 0.303 × 103 mM−1 s−1 using triolein as substrate. Natural detergents, such as sodium deoxycholate, act as potent inhibitors of the lipase. This inhibition can be reversed by adding fresh oil emulsion. Result with tetrahydrolipstatin, an irreversible inhibitor, suggests that the lipase is a serine enzyme. Peptide sequences of the lipase were determined and compared with the full-length sequence of lipase which was obtained by the rapid amplification of cDNA ends method. The full cDNA of the pvl was 1,186 bp, with a deduced protein of 362 amino acids that includes a consensus sequence (GXSXG) of the lipase superfamily of α/β-hydrolase. The gene exhibits features of conserved catalytic residues and high homology with various mammalian and insect lipase genes. A potential lid sequence is suggested for pvl.