Now that enzymes are available that are stable above 100 °C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon stabilizing forces arising from a large number of weak interactions, which are opposed by an almost equally large destabilizing force due mostly to conformational entropy. The difference between these, the net free energy of stabilization, is relatively small, equivalent to a few interactions. The enhanced stability of very stable proteins can be achieved by an additional stabilizing force which is again equivalent to only a few stabilizing interactions. There is currently no strong evidence that any particular interaction (e.g. hydrogen bonds, hydrophobic interactions) plays a more important role in proteins that are stable at 100 °C than in those stable at 50 °C, or that the structures of very stable proteins are systematically different from those of less stable proteins. The major degradative mechanisms are deamidation of asparagine and glutamine, and succinamide formation at aspartate and glutamate leading to peptide bond hydrolysis. In addition to being temperature-dependent, these reactions are strongly dependent upon the conformational freedom of the susceptible amino acid residues. Evidence is accumulating which suggests that even at 100 °C deamidation and succinamide formation proceed slowly or not at all in conformationally intact (native) enzymes. Whether this is the case at higher temperatures is not yet clear, so it is not known whether denaturation or degradation will set the upper limit of stability for enzymes.
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July 1996
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Review Article|
July 01 1996
The denaturation and degradation of stable enzymes at high temperatures
Roy M. DANIEL;
Roy M. DANIEL
*
1Department of Biological Sciences, The University of Waikato, Hamilton, New Zealand
*To whom correspondence should be addressed.
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Mark DINES;
Mark DINES
1Department of Biological Sciences, The University of Waikato, Hamilton, New Zealand
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1996
1996
Biochem J (1996) 317 (1): 1–11.
Citation
Roy M. DANIEL, Mark DINES, Helen H. PETACH; The denaturation and degradation of stable enzymes at high temperatures. Biochem J 1 July 1996; 317 (1): 1–11. doi: https://doi.org/10.1042/bj3170001
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