We have studied the catalytic efficiency of acetylcholinesterase (AChE) in various solutions with ion-disturbed water structure to explore the role that the water structure plays in the substrate-enzyme encounter. The extent of water structuring in the different aqueous solutions was determined by near-infrared spectroscopy. The influence of water structure on the degree of solvation and on the intramolecular mobility of AChE was investigated for different aqueous ionic solutions by small-angle x-ray scattering technique and depolarization fluorescence spectroscopy. It was found that the encounter process between AChE and acetylthiocholine was promoted in solutions with less structured water. In these solutions it was also found that AChE is less solvated coinciding with higher intramolecular mobility. The found experimental results suggest that the water structure may influence the substrate-enzyme encounter process by diminishing the AChE solvation shell and may help diffusion of the substrate through the gorge by enhancing the intramolecular mobility of AChE.
Permittivity is a very important physical parameter for a detailed understanding of interactions in a biological system. However, at the moment no common experimental method is available for measuring the dielectric constants of a microenvironment or on a local level, and one has to rely on theoretical simulations. In this work we can demonstrate that it is experimentally possible to estimate the dielectric constant of the active site of the enzyme acetylcholinesterase, based on the spectroscopic properties of the laser dye N,N-dimethyl(4-pyren-1ylphenyl)amine. It was found that the dye specifically attaches to the active site of acetylcholinesterase and therefore inhibits its functionality. The microenvironmental dielectric properties, which are spectroscopically sensed, and enzymatic functionality can be combined and might potentially be developed to a biosensing element.
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