On the behavior of acetylcholinesterase immobilized on carbon nanotubes in the presence of inhibitors

The behavior of acetylcholinesterase before and after click-chemistry reaction on carbon nanotubes was evaluated by kinetic parameters from Michaelis–Menten equation. These data were obtained by means of UV–vis absorption for the enzyme in solution and attached to MWCNTs under two experimental conditions involving the presence or absence of enzyme inhibitors (chlorpyrifos and paraoxon pesticides). After the immobilization step it was possible to obtain, from Michaelis–Menten equation, Km values comparable to those for free enzyme, suggesting that the immobilization procedure does not affect the enzyme–substrate interaction. On the other hand, the Vmax value decreased about 45-fold, pointing out that enzyme activity is slowed by immobilization on MWCNTs. We were able to demonstrate that this is caused by competition between the MWCNTs and acetylthiocholine for the active sites of AChE. In the presence of inhibitors some change was observed in terms of mechanistic aspects. These results are important to improve understanding of the potential of enzyme–carbon nanotube complexes to expand the biological, medical, and environmental applications of CNT materials.