TY  - JOUR
AU  - Duy, C.
AU  - Fitter, J.
TI  - Thermostability of Irreversible Unfolding alpha-Amylases Analyzed by Unfolded Kinetics
JO  - The journal of biological chemistry
VL  - 280
SN  - 0021-9258
CY  - Bethesda, Md.
PB  - Soc.
M1  - PreJuSER-49011
SP  - 37360 - 37365
PY  - 2005
N1  - Record converted from VDB: 12.11.2012
AB  - For most multidomain proteins the thermal unfolding transitions are accompanied by an irreversible step, often related to aggregation at elevated temperatures. As a consequence the analysis of thermostabilities in terms of equilibrium thermodynamics is not applicable, at least not if the irreversible process is fast with respect the structural unfolding transition. In a comparative study we investigated aggregation effects and unfolding kinetics for five homologous alpha-amylases, all from mesophilic sources but with rather different thermostabilities. The results indicate that for all enzymes the irreversible process is fast and the precedent unfolding transition is the rate-limiting step. In this case the kinetic barrier toward unfolding, as measured by unfolding rates as function of temperature, is the key feature in thermostability. The investigated enzymes exhibit activation energies (E(a)) between 208 and 364 kJmol(-1) and pronounced differences in the corresponding unfolding rates. The most thermostable alpha-amylase from Bacillus licheniformis (apparent transition temperature, T(1/2) approximately 100 degrees C) shows an unfolding rate which is four orders of magnitude smaller as compared with the alpha-amylase from pig pancreas (T(1/2) approximately 65 degrees C). Even with respect to two other alpha-amylases from Bacillus species (T(1/2) approximately 86 degrees C) the difference in unfolding rates is still two orders of magnitude.
KW  - Animals
KW  - Aspergillus oryzae: enzymology
KW  - Bacillus: enzymology
KW  - Circular Dichroism
KW  - Enzyme Stability
KW  - Hot Temperature
KW  - Kinetics
KW  - Protein Denaturation
KW  - Protein Folding
KW  - Swine
KW  - Thermodynamics
KW  - Transition Temperature
KW  - alpha-Amylases: chemistry
KW  - alpha-Amylases: metabolism
KW  - alpha-Amylases (NLM Chemicals)
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
C6  - pmid:16150692
UR  - <Go to ISI:>//WOS:000233044500009
DO  - DOI:10.1074/jbc.M507530200
UR  - https://juser.fz-juelich.de/record/49011
ER  -