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: Elucidating the sugar import pathway into developing kiwifruit berries (Actinidia deliciosa)

authors: Gould, Nick

subjects: carbon-14

abstract: The aim of this work was to investigate the roles of the apoplasmic and symplasmic pathways in the delivery of solutes to the outer pericarp of developing green-fleshed kiwifruit berries (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa ‘Hayward’). Experiments with the symplasmic tracer 5(6)-carboxyfluorescein (CF) showed symplasmic movement of dye during the initial rapid growth stage of the fruit, but as fruit growth slowed and starch content increased, a reduction in symplasmic spread of CF was observed (+126 DAA [days after anthesis]). Measurements of sugar uptake rates from the apoplasm were sufficient to account for the dry matter accumulation in growing fruit at each stage of fruit growth, and could potentially operate alongside a symplasmic pathway for post-phloem unloading of sugars during the rapid growth period. Energy requirements driving uptake from the apoplasm appear to depend on the sugar concentration gradients across the cell membrane throughout fruit development. Together, these data suggest: 1) the post-phloem symplasmic pathway is important during the fruit rapid growth stage, 2) the uptake of sugars from the apoplasm has a role in the transport of carbohydrates in the fruit, especially later in fruit development when the symplasmic pathway is reduced, and 3) apoplasmic sugar has an important role in the flow of water into the apoplasm of the fruit, providing a mechanism to maintain hydrostatic pressure gradients along the phloem supplying the fruit.

text: Elucidating the sugar import pathway into developing kiwifruit berries (Actinidia deliciosa) The aim of this work was to investigate the roles of the apoplasmic and symplasmic pathways in the delivery of solutes to the outer pericarp of developing green-fleshed kiwifruit berries (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa ‘Hayward’). Experiments with the symplasmic tracer 5(6)-carboxyfluorescein (CF) showed symplasmic movement of dye during the initial rapid growth stage of the fruit, but as fruit growth slowed and starch content increased, a reduction in symplasmic spread of CF was observed (+126 DAA [days after anthesis]). Measurements of sugar uptake rates from the apoplasm were sufficient to account for the dry matter accumulation in growing fruit at each stage of fruit growth, and could potentially operate alongside a symplasmic pathway for post-phloem unloading of sugars during the rapid growth period. Energy requirements driving uptake from the apoplasm appear to depend on the sugar concentration gradients across the cell membrane throughout fruit development. Together, these data suggest: 1) the post-phloem symplasmic pathway is important during the fruit rapid growth stage, 2) the uptake of sugars from the apoplasm has a role in the transport of carbohydrates in the fruit, especially later in fruit development when the symplasmic pathway is reduced, and 3) apoplasmic sugar has an important role in the flow of water into the apoplasm of the fruit, providing a mechanism to maintain hydrostatic pressure gradients along the phloem supplying the fruit.

year: 2013

title: Haumanu Hauora: Strengthening health institution responsiveness to climate change

authors: Masters-Awatere, Bridgette

abstract: The “Haumanu Hauora: Strengthening health institution responsiveness to climate change” project (Haumanu Hauora) is funded by the Deep South National Science Challenge. Our research team has 
been working to determine how health institutions (for example DHBs) develop Māori responsive policy as a preparatory step in anticipation of climate change impacts on Māori health. The project 
has involved several components, one of which involved speaking with tāngata whenua and DHB staff from the Bay of Plenty, Lakes and Waikato DHB regions about their experiences of climate 
change and involvement with health services. Another component was an environmental scan of available website information on the 17 other DHBs to ascertain the extent of policy that speaks to 
both the Treaty of Waitangi and climate change. This report presents an overview of the findings. 

This report begins with some context setting. We provide a summary of our literature reviews before a brief outline of the establishment of DHBs, which are the “health institution” of focus for 
this research. As the primary health provider and funders around the country, DHBs have been engaged as the site through which to understand the Māori health and climate change policy needs. 
Although DHBs were disestablished at the conclusion of our project, there are still lessons to learn from the ‘old’ health system. We present themes from tāngata whenua and rangatahi interviews as 
a way to foreground policy development information provided by DHB staff.

text: Haumanu Hauora: Strengthening health institution responsiveness to climate change The “Haumanu Hauora: Strengthening health institution responsiveness to climate change” project (Haumanu Hauora) is funded by the Deep South National Science Challenge. Our research team has 
been working to determine how health institutions (for example DHBs) develop Māori responsive policy as a preparatory step in anticipation of climate change impacts on Māori health. The project 
has involved several components, one of which involved speaking with tāngata whenua and DHB staff from the Bay of Plenty, Lakes and Waikato DHB regions about their experiences of climate 
change and involvement with health services. Another component was an environmental scan of available website information on the 17 other DHBs to ascertain the extent of policy that speaks to 
both the Treaty of Waitangi and climate change. This report presents an overview of the findings. 

This report begins with some context setting. We provide a summary of our literature reviews before a brief outline of the establishment of DHBs, which are the “health institution” of focus for 
this research. As the primary health provider and funders around the country, DHBs have been engaged as the site through which to understand the Māori health and climate change policy needs. 
Although DHBs were disestablished at the conclusion of our project, there are still lessons to learn from the ‘old’ health system. We present themes from tāngata whenua and rangatahi interviews as 
a way to foreground policy development information provided by DHB staff.

year: 2022-07-12