title: Review: The denaturation and degradation of stable enzymes at high temperatures

authors: Daniel, Roy M.

subjects: enzyme

abstract: 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.

text: Review: The denaturation and degradation of stable enzymes at high temperatures 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.

year: 1996

title: Book review: Education, disordered eating and obesity discourse: fat fabrications

authors: lisahunter

subjects: book review

abstract: This book reviews the book, “Education, disordered eating and obesity discourse: fat fabrications”, edited by J. Evans, E. Rich, B. Davies & R. Allwood.

text: Book review: Education, disordered eating and obesity discourse: fat fabrications This book reviews the book, “Education, disordered eating and obesity discourse: fat fabrications”, edited by J. Evans, E. Rich, B. Davies & R. Allwood.

year: 2010

title: He pao

authors: Roa, Tom

subjects: Pao

abstract: Ko Te Whare Wānanga O Waikato" te ingoa o tētehi pao nāku i tito hei waiata mā Te Whare Wānanga O Waikato, i te tau 2004.

text: He pao Ko Te Whare Wānanga O Waikato" te ingoa o tētehi pao nāku i tito hei waiata mā Te Whare Wānanga O Waikato, i te tau 2004.

year: 2012-05