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This work proposes a simple, cost-effective, and efficient preparation of a composite made from magnetic diatomaceous earth (mDE) coated with polyaniline (mDE@PANI). The material was used as a matrix for immobilizing industrial enzymes: invertase, β-galactosidase, and trypsin. The mDE@PANI was characterized by several methods, and the results suggested that the nanoparticles were approximately 12 nm in size, exhibited superparamagnetic behavior, and displayed a good magnetic response and that magnetite comprised the main iron oxide phase. Moreover, several studies were conducted for all immobilized derivatives, including determination of optimal pH and temperature; kinetic parameters; thermal stability and reusability. The obtainment of three novel magnetic biocatalysts with superior performance (in terms of activity and stability) compared to their free counterparts demonstrated the efficacy of the mDE@PANI nanoparticles. In addition, the enzymatic derivatives can be easily recovered from the reactor by using an external magnetic field. Finally, the present methodology allowed the achievement of good mDE@PANI matrix together with three promising magnetic biocatalysts with several potential biotechnological applications. [ABSTRACT FROM AUTHOR]

This contribution aimed to characterize physicochemical and kinetic parameters of the brain cholinesterases (ChEs) from Parachromis managuensis and investigate the in vitro effects of pesticides and metal ions on its activity intending to propose as biomarker. This species is suitable for this investigation because (1) it was recently introduced in Brazil becoming invasive (no restrictions on capture) and (2) occupies the top of the food chain (being subject to bioaccumulation). The enzyme extract was exposed to 10 metal ions (Al 3+ , Ba 2+ , Cd 2+ , Cu 2+ , Hg 2+ , Mg 2+ , Mn 2+ , Pb 2+ , Fe 2+ and Zn 2+ ) and ChEs selective inhibitors (BW284c51, Iso-OMPA, neostigmine and serine). The extract was also incubated with organophosphate (dichlorvos) and carbamate pesticides (carbaryl and carbofuran). Inhibition parameters (IC 20 , IC 50 and ki) were determined. Selective inhibitors and kinetic parameters confirmed acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) -like as responsible for the ChE activities, most AChE. The IC 50 values for pesticides were: 1.68 μM (dichlorvos); 4.35 μM (carbaryl) and 0.28 μM (carbofuran). Most of the analyzed ions did not show significant effect at 1 mM ( p = 0.05), whereas the following ions inhibited the enzyme activity in the order: Hg 2+ > Cu 2+ > Cd 2+ > Zn 2+ . Mercury ion strongly inhibited the enzyme activity (IC 20 = 0.7 μM). The results about allow to conclude that P. managuensis brain AChE is a potential biomarker for heavy metals and pesticides under study, mainly for the carbamate carbofuran once it was capable to detect 6-fold lower levels than the limit concentration internationally recommended. [ABSTRACT FROM AUTHOR]