Interaction of cellulase with cationic surfactants: using surfactant membrane selective electrodes and fluorescence...

The interaction of cationic surfactants, n-alkyl trimethyl ammonium bromides (CnTAB, n = 12 and 14), with cellulase from Aspergillus niger has been investigated at 25 degrees C and various pH, using CnTAB-membrane selective electrodes as a simple, fast, cheap and accurate technique and fluorescence spectroscopy. The regions of C1 (the surfactant concentration at which binding is initiated) and C2 (enzyme saturated by surfactant) were determined using potentiometric measurements. The obtained binding isotherms have been analyzed using Scatchard plot and binding capacity concept. The results were interpreted on the basis of nature of forces which interfered in the interaction and represent two binding sets system for all of the studied conditions. Hill equation parameters have been estimated and used for calculation of intrinsic Gibbs free energy that decreases with extension of binding. The effect of CnTAB binding on cellulase intrinsic fluorescence spectra was also examined. A biphasic behavior was observed for quenching process of endoglucanase by CnTAB that confirms the results of binding studies correspond to the existence of two types of binding sites for CnTAB on cellulase.