title: Change in heat capacity for enzyme catalysis determines temperature dependence of enzyme catalyzed ratesnzyme Catalyzed Rates

authors: Hobbs, Joanne K.

abstract: The increase in enzymatic rates with temperature up to an optimum temperature (Topt) is widely attributed to classical Arrhenius behavior, with the decrease in enzymatic rates above Topt ascribed to protein denaturation and/or aggregation. This account persists despite many investigators noting that denaturation is insufficient to explain the decline in enzymatic rates above Topt. Here we show that it is the change in heat capacity associated with enzyme catalysis (ΔC‡p) and its effect on the temperature dependence of ΔG‡ that determines the temperature dependence of enzyme activity. Through mutagenesis, we demonstrate that the Topt of an enzyme is correlated with ΔC‡p and that changes to ΔC‡p are sufficient to change Topt without affecting the catalytic rate. Furthermore, using X-ray crystallography and molecular dynamics simulations we reveal the molecular details underpinning these changes in ΔC‡p. The influence of ΔC‡p on enzymatic rates has implications for the temperature dependence of biological rates from enzymes to ecosystems.

text: Change in heat capacity for enzyme catalysis determines temperature dependence of enzyme catalyzed ratesnzyme Catalyzed Rates The increase in enzymatic rates with temperature up to an optimum temperature (Topt) is widely attributed to classical Arrhenius behavior, with the decrease in enzymatic rates above Topt ascribed to protein denaturation and/or aggregation. This account persists despite many investigators noting that denaturation is insufficient to explain the decline in enzymatic rates above Topt. Here we show that it is the change in heat capacity associated with enzyme catalysis (ΔC‡p) and its effect on the temperature dependence of ΔG‡ that determines the temperature dependence of enzyme activity. Through mutagenesis, we demonstrate that the Topt of an enzyme is correlated with ΔC‡p and that changes to ΔC‡p are sufficient to change Topt without affecting the catalytic rate. Furthermore, using X-ray crystallography and molecular dynamics simulations we reveal the molecular details underpinning these changes in ΔC‡p. The influence of ΔC‡p on enzymatic rates has implications for the temperature dependence of biological rates from enzymes to ecosystems.

year: 2013

title: Tephrochronology of last termination sequences in Europe: a protocol for improved analytical precision and robust correlation procedures (a joint SCOTAV–INTIMATE proposal)

authors: Turney, Chris S.M.

subjects: basaltic and rhyolitic tephra

abstract: The precise sequence of events during the Last Termination (18 000–9000 ka 14C yr BP), and the extent to which major environmental changes were synchronous, are difficult to establish using the radiocarbon method alone because of serious distortions of the radiocarbon time-scale, as well as the influences of site-specific errors that can affect the materials dated. Attention has therefore turned to other methods that can provide independent tests of the chronology and correlation of events during the Last Termination. With emphasis on European sequences, we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role. Recent advances in the detection and analysis of ‘hidden’ tephra layers (cryptotephra) indicate that some tephras of Last Termination age are much more widespread in Europe than appreciated hitherto, and a number of new tephra deposits have also been identified. There is much potential for developing an integrated tephrochronological framework for Europe, which can help to underpin the overall chronology of events during the Last Termination. For that potential to be realised, however, there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past. We propose a protocol for improving analytical and reporting procedures, as well as the establishment of a centralised data base of the results, which will provide an important geochronological tool to support a diverse range of stratigraphical studies, including opportunities to reassess volcanic hazards. Although aimed primarily at Europe, the protocol proposed here is of equal relevance to other regions and periods of interest.

text: Tephrochronology of last termination sequences in Europe: a protocol for improved analytical precision and robust correlation procedures (a joint SCOTAV–INTIMATE proposal) The precise sequence of events during the Last Termination (18 000–9000 ka 14C yr BP), and the extent to which major environmental changes were synchronous, are difficult to establish using the radiocarbon method alone because of serious distortions of the radiocarbon time-scale, as well as the influences of site-specific errors that can affect the materials dated. Attention has therefore turned to other methods that can provide independent tests of the chronology and correlation of events during the Last Termination. With emphasis on European sequences, we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role. Recent advances in the detection and analysis of ‘hidden’ tephra layers (cryptotephra) indicate that some tephras of Last Termination age are much more widespread in Europe than appreciated hitherto, and a number of new tephra deposits have also been identified. There is much potential for developing an integrated tephrochronological framework for Europe, which can help to underpin the overall chronology of events during the Last Termination. For that potential to be realised, however, there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past. We propose a protocol for improving analytical and reporting procedures, as well as the establishment of a centralised data base of the results, which will provide an important geochronological tool to support a diverse range of stratigraphical studies, including opportunities to reassess volcanic hazards. Although aimed primarily at Europe, the protocol proposed here is of equal relevance to other regions and periods of interest.

year: 2004

title: The Application of Critical Discourse Theory: A Criterion-Referenced Analysis of Reports Relating to Language Revitalisation in Australia and New Zealand

authors: Lewis, Roger Brian

subjects: te reo Māori

abstract: The discipline of language policy and planning (LPP) is often proposed as a viable tool for language revitalisation. However, the conventional paradigm upon which LPP is based is inadequate for such an inherently political, contentious and problematic area of social policy, and does not address the hegemonic and counter-hegemonic discourse that is at the very core of language revitalisation efforts. It is therefore argued here that LPP needs to be explicitly underpinned by critical discourse theory (CDT) if it is to be of genuine use to those involved in language revitalisation efforts, particularly to grass roots language activists. Following an introductory chapter which provides a background to the research and a rationale for it (Chapter 1), there is a critical review of selected literature on LPP and CDT, a review which ends by proposing a list of criteria which, it is argued, can be used to determine the extent to which discourse that is intended to be counter-hegemonic adheres to the principles of effective counter-hegemonic discourse as outlined in the literature on CDT (Chapter 2). In the following three chapters (Chapters 3, 4 & 5), these criteria are applied to the analysis of three recent reports that have a direct bearing on indigenous language revitalisation in Australia (Our Land Our Languages) and New Zealand (Ko Aotearoa Tēnei and Te Reo Mauriora). The first of these reports is found to adhere very closely to the criteria; the second less so; the third almost not at all. The different ways in which each of these reports has been received would tend to support the hypothesis that, other things being equal, the more closely a text of this type conforms to the criteria - that is, the more closely it is aligned to the fundamental principles of effective counter-hegemonic discourse as outlined in CDT - the more likely it is to be positively received and, therefore, to represent an effective challenge to the existing hegemony. The overall conclusion is that CDT can not only assist language activists by providing a basis for determining how successful counter-hegemonic discourse is likely to be in achieving its aims but has the potential to provide LPP with a secure theoretical foundation (Chapter 6).

text: The Application of Critical Discourse Theory: A Criterion-Referenced Analysis of Reports Relating to Language Revitalisation in Australia and New Zealand The discipline of language policy and planning (LPP) is often proposed as a viable tool for language revitalisation. However, the conventional paradigm upon which LPP is based is inadequate for such an inherently political, contentious and problematic area of social policy, and does not address the hegemonic and counter-hegemonic discourse that is at the very core of language revitalisation efforts. It is therefore argued here that LPP needs to be explicitly underpinned by critical discourse theory (CDT) if it is to be of genuine use to those involved in language revitalisation efforts, particularly to grass roots language activists. Following an introductory chapter which provides a background to the research and a rationale for it (Chapter 1), there is a critical review of selected literature on LPP and CDT, a review which ends by proposing a list of criteria which, it is argued, can be used to determine the extent to which discourse that is intended to be counter-hegemonic adheres to the principles of effective counter-hegemonic discourse as outlined in the literature on CDT (Chapter 2). In the following three chapters (Chapters 3, 4 & 5), these criteria are applied to the analysis of three recent reports that have a direct bearing on indigenous language revitalisation in Australia (Our Land Our Languages) and New Zealand (Ko Aotearoa Tēnei and Te Reo Mauriora). The first of these reports is found to adhere very closely to the criteria; the second less so; the third almost not at all. The different ways in which each of these reports has been received would tend to support the hypothesis that, other things being equal, the more closely a text of this type conforms to the criteria - that is, the more closely it is aligned to the fundamental principles of effective counter-hegemonic discourse as outlined in CDT - the more likely it is to be positively received and, therefore, to represent an effective challenge to the existing hegemony. The overall conclusion is that CDT can not only assist language activists by providing a basis for determining how successful counter-hegemonic discourse is likely to be in achieving its aims but has the potential to provide LPP with a secure theoretical foundation (Chapter 6).

year: 2014