Utilization of Cross-Linked Laccase Aggregates in a Perfusion Basket Reactor for the Continuous Elimination of Endocrine-Disrupting Chemicals

A perfusion basket reactor (BR) was developed for the continuous utilization of insolubilized laccase as cross-linked enzyme aggregates (CLEAs). The BR consisted of all unbaffled basket made of a metallic filtration module filled with, CLEAs and continuously agitated by a 3-blade marine propeller. The agitation conditions influenced both the apparent laccase activity in the reactor and the stability of the biocatalyst. Optimal laccase activity was obtained at a rotational speed of 12.5 rps and the highest stability was reached at speeds of 1.7 rps or lower. The activity and stability of the biocatalyst were affected drastically upon the appearance of vortices in the reaction medium. This reactor was used for the continuous elimination of the endocrine disrupting chemicals (EDCs) nonylphenol (NP), bisphenol A (BPA), and triclosan (TCS). Optimization of EDC elimination by laccase CLEAs as a function of temperature and pH was achieved by response surface methodology using a central composite factorial design. The optimal conditions of pH and temperature were, respectively, 4.8 and 40.3 degrees C for the elimination of p353NP (a branched isomer of NIP), 4.7 and 48.0 degrees C for BPA, and 4.9 and 41.2 degrees C for TCS. Finally, the BR was used for the continuous elimination of these EDCs from a 5 mg L-1 aqueous solution using I mg of CLEAs at pH 5 and room temperature. Our results showed that at least 85% of these EDCs could be eliminated with a hydraulic retention time of 325 min. The performances of the BR were quite stable over a 7-day period of continuous treatment. Furthermore, this system could eliminate the same EDCs from a 100 mg L-1 solution. Finally, a mathematical model combining the Michaelis-Menten kinetics of the laccase CLEAs and the continuous stirred tank reactor behavior of the BR was developed to predict the elimination of these xenobiotics. Biotechnol. Bioeng. 2009;102: 1582-1592. (C) 2008 Wiley Periodicals, Inc

Do Protein Molecules Unfold in a Simple Shear Flow?

Protein molecules typically unfold (denature) when subjected to extremes of heat, cold, pH, solvent composition, or mechanical stress. One might expect that shearing forces induced by a nonuniform fluid flow would also destabilize proteins, as when a protein solution flows rapidly through a narrow channel. However, although the protein literature contains many references to shear denaturation, we find little quantitative evidence for the phenomenon. We have investigated whether a high shear can destabilize a small globular protein to any measurable extent. We study a protein (horse cytochrome c, 104 amino acids) whose fluorescence increases sharply upon unfolding. By forcing the sample through a silica capillary (inner diameter 150–180 μm) at speeds approaching 10 m/s, we subject the protein to shear rates dv(z)/dr as large as ∼2 × 10(5) s(−1) while illuminating it with an ultraviolet laser. We can readily detect fluorescence changes of <1%, corresponding to shifts of <∼0.01 kJ/mol in the stability of the folded state. We find no evidence that even our highest shear rates significantly destabilize the folded protein. A simple model suggests that extraordinary shear rates, ∼10(7) s(−1), would be required to denature typical small, globular proteins in water

Newly proposed therapy-related myelodysplastic syndrome prognostic score predicts significant differences in overall survival and leukemia-free survival in patients treated with azacitidine

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