The Structural and Molecular Dynamics of Salt Activation

Enzyme flexibility is greater in solvents with high polarity because of weaker electrostatic interactions in these solvents [54, 104, 105]. The loss in enzyme activity seen in the NMR study described above may be attributed to the water stripping model as water is stripped from the enzyme, locations in and on the enzyme previously inaccessible to the solvent may become accessible, thus permitting increased solvent-enzyme interactions [103]. As a result, enzyme structure may be disrupted (e.g., partially denatured), and catalytic activity is decreased. The partially denatured enzyme appears to exhibit greater flexibility as solvent polarity increases [106, 107]. 

Eppler et al. [103] viewed these results as having a potential relationship to salt-activated enzyme preparations, particularly in relation to the mobility of enzyme-bound water. Specifically, the authors examined both water mobility [as measured by T2-derived correlation times, (tc)D20] and NaF-activated enzyme activity and observed a linear relationship. This suggests that the salt-activated enzymes contain a more mobile water population than salt-free enzymes, which facilitates a more aqueous-like local environment and dramatically increases enzyme activity through increased flexibility. Therefore, enzyme activation appears to correlate with the properties of enzyme-associated water. Once again, the physicochemical properties of water dictate enzyme structure, function, and dynamics. Hence, salt activation has proven to be a useful technique in activating enzymes for use in organic solvents and has provided a quantitative tool to better understand the role of water in enzymatic catalysis in dehydrated media. 

21 Falconi, M., Brunelli, M., Pesce, A., Ferrario, M., Bolognesi, M., Desideri, A. (2003) Proteins Struct. Fund. Genet. 51, 607-615. 

43 Persson, M., Mladenoska, I., Wehtje, E., Adlercreutz, P. (2002) Enzyme Microb. Technol. 31, 833-841. 

62 Ohe, S. (1989) Vapor-Equilibrium Data (Elsevier, Kodansha, Tokyo). 

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