Stability Studies of Gold Nanoparticles Immobilized Soybean Urease on Exposure to Metal Ions and Organic Solvents

Immobilization of enzymes enhances their properties for economical utilization in industrial processes. In the present study, urease was immobilized on cysteine modified gold nanoparticles. Physicochemical characterization of the immobilized urease was performed by means of Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscope (TEM). Results showed high immobilization with binding efficiency of 82%. The binding capacity of urease onto nanoparticles reached 430μg/mg. The optimal pH shifted from 7.5 for soluble urease to 8.0 for the immobilized urease and the optimal temperature shifted from 60ºC to 70ºC. Km values of the soluble and immobilized urease were 14.20 mM and 16.65 mM, respectively. The effect of metal ions on soluble and immobilized urease was studied. Effect of various organic solvents like methanol, ethanol, propanol, acetone, acetonitrile and dimethylformamide on the activity of free enzyme as well as immobilized enzyme was explored and it was found that immobilized enzyme was more stable at higher concentrations of organic solvents. Overall, this study showed that the stability and activity of the urease were enhanced via cross linking to the gold nanoparticles suggesting that immobilized enzyme could be used in an interesting range of biological applications.