Stabilization of D-lactate dehydrogenase diagnostic enzyme via immobilization on pristine and carboxyl-functionalized carbon nanotubes, a combined experimental and molecular dynamics simulation study

The most important mode of enzyme inactivation is thermal inactivation. Immobilization technology is an efficient approach to elongate the life-time of enzymes. D-lactate dehydrogenase (D-LDH) was stabilized at high temperatures with immobilization on CNT and fCNT. The kinetic and thermodynamic parameters, optimum temperature and pH, and the intrinsic fluorescence of free and immobilized enzymes were examined in the present study. Also, an attempt was made to investigate the effect of CNT and fCNT on the adsorption and conformation of D-lactate dehydrogenase using molecular dynamics (MD) simulations. In comparison with free enzyme, the immobilized enzyme displayed an improved stability at high temperatures and, therefore, the immobilized enzyme is suitable for use in the industry because most reactions in the industry happen at high temperatures. Results of the present study showed that the adsorption of enzyme on CNT is mediated through the van der Waals and pi-pi stacking interactions, whereas in the adsorption of enzyme on fCNT in addition to hydrophobic interactions, the hydrogen bonding between enzyme and functional groups of fCNT is involved. Moreover, RMSD, RMSF and secondary structure analysis indicate that the fCNT protects the conformation of enzyme more than CNT. Therefore, D-LDH can be efficiently immobilized upon the fCNT compared to the pristine CNT.