Spectroscopic study on the interaction of Bacillus subtilis α-amylase with cetyltrimethylammonium bromide

The interaction between alpha-amylase from Bacillus subtilis and cetyltrimethylammonium bromide (CTAB) has been investigated at various temperature conditions using fluorescence and circular dichroism (CD) spectroscopic methods. Fluorescence data revealed that the fluorescence quenching of alpha-amylase by CTAB is the result of complex formation between CTAB and alpha-amylase. The thermodynamic analysis on the binding interaction data shows that the interactions are strongly exothermic (Delta H degrees = -17.92 kJ mol(-1)) accompanied with increase in entropy (Delta S degrees between 109 to 135J mol(-1) K-1). Thus the binding of CTAB to alpha-amylase is both enthalpic and entropic driven, which represent the predominate role of both electrostatic and hydrophobic interactions in complex formation process. The values of 2.17 x 10(-3) M-1 and 1.30 have been obtained from associative binding constant (K-a) and stoichiometry of binding number (n), from analysis of fluorescence data, respectively. Circular dichroism spectra showed the substantial conformational changes in secondary structure of alpha-amylase due to binding of CAB, which represents the complete destruction of both secondary and tertiary structure of alpha-amylase by CTAB. (C) 2011 Elsevier B.V. All rights reserved.