Differential scanning calorimetric studies of a Bacillus halodurans alpha-amylase

The thermal unfolding of Amy 34, a recombinant alpha-amylase from Bacillus halodurans, has been investigated using differential scanning calorimetry (DSC). The denaturation of Amy 34 involves irreversible processes with an apparent denaturation temperature (T-m) of 70.8 degrees C at PH 9.0, with four transitions, as determined using multiple Gaussian curves. The T-m increased by 5 degrees C in the presence of 100-fold molar excess of CaCl2 while the aggregation of Amy 34 was observed in the presence of 1000-fold molar excess of CaCl2. Increase in the calcium ion concentration from 1 - to 5-fold molar excess resulted in an increase in calorimetric enthalpy (Delta H-cal), however, at higher concentrations of CaCl2 (up to 100-fold), Delta H-cal was found to decrease, accompanied by a decrease in entropy change (Delta S), while the T., steadily increased. The presence of 100-fold excess of metal chelator, EDTA, resulted in a decrease in T-m by 10.4 degrees C. T-m was also decreased to 61.1 degrees C and 65.9 degrees C at PH 6.0 and PH 11.0, respectively. (c) 2005 Elsevier B.V. All rights reserved.