Enzyme immobilization and molecular modeling studies on an organic-inorganic polypyrrole-titanium(IV)phosphate nanocomposite

In this work we report the synthesis of an electrically conductive polypyrrole-titanium(IV)phosphate (PPy-TiP) nanocomposite using simple, facile in situ chemical oxidative polymerization of polypyrrole (PPy) in the presence of titanium(iv)phosphate (TiP) for immobilization of the yeast alcohol dehydrogenase enzyme. FTIR, FE-SEM and TGA were employed for the characterization of PPy, TiP and the PPy-TiP nanocomposite. YADH was successfully immobilized on the PPy-TiP nanocomposite with a loading efficiency of 69%. The immobilized YADH showed no change in the pH optima (pH 8.0) and there was a broadening of the peak both at acidic as well as in alkaline pH. The optimum temperature of immobilized YADH was increased by 5 °C with almost the same residual activity. Immobilized YADH showed improved thermal stability at 60 °C and retained about 71% activity after 5 h of incubation. Also, the immobilized YADH showed greater reusability and retained 75% activity after 10th successive use. All the results were compared to those of free YADH, immobilized YADH on PPy and immobilized YADH on TiP. The affinity of immobilized YADH for ethanol was decreased as evident from the K_m value (223.71 mM) and also there was a decrease in the maximum velocity (201.53 μM min^-1) as compared to soluble YADH. The improved residual activity, stability and reusability of YADH immobilized on the PPy-TiP nanocomposite make the enzyme more suitable for industry-based applications. Molecular docking was used to query the protein - the newly synthesized chemical entity interactions that help in understanding the affinity in enzyme activity.