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 (DeltaH(cal)), however, at higher concentrations of CaCl2 (up to 100-fold), DeltaH(cal) was found to decrease, accompanied by a decrease in entropy change (DeltaS), while the T(m) 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.
Hashim
Suhaila O
SO
Department of Biotechnology, Center for Chemistry and Chemical Engineering, Lund University, Box 124, SE-221 00 Lund, Sweden. suhaila.hashim@biotek.lu.se
Kaul
Rajni-Hatti
RH
Andersson
Maria
M
Mulaa
Francis J
FJ
Mattiasson
Bo
B
D001407:Bacillus / Q000201:enzymology*; D002122:Calcium Chloride / Q000494:pharmacology; D002152:Calorimetry, Differential Scanning; D004492:Edetic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D011489:Protein Denaturation; D017510:Protein Folding; D013816:Thermodynamics; D000516:alpha-Amylases / Q000737:chemistry*
D004492:Edetic Acid; D000516:alpha-Amylases; D002122:Calcium Chloride