title: A new intrinsic thermal parameter for enzymes reveals true temperature optima

authors: Peterson, Michelle E.

subjects: enzyme

abstract: Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, Teq, arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source (“evolved”) temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, Teq is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on Teq with respect to enzyme temperature/activity effects to be more important than on thermal stability. Teq is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution.

text: A new intrinsic thermal parameter for enzymes reveals true temperature optima Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, Teq, arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source (“evolved”) temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, Teq is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on Teq with respect to enzyme temperature/activity effects to be more important than on thermal stability. Teq is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution.

year: 2004

title: Comparison of cellulolytic activities in Clostridium thermocellum and Three thermophilic, cellulolytic anaerobes

authors: Reynolds, Paul H.S.

subjects: carboxymethyl cellulose

abstract: Avicelase, carboxymethyl cellulase (CMCase), and β-glucosidase activities have been compared between Clostridium thermocellum and three extremely thermophilic, cellulolytic anaerobes, isolates TP8, TP11, and KT8. The three isolates were all small, gram-negative staining, oval-ended rods which occurred singly and, at exponential phase, in long chains. They were nonflagellated and no spores were visible. The KT8 and TP11 isolates caused clumping of the cellulose during growth. In all four organisms the CMCase activity paralleled cell growth; however, in C. thermocellum and TP8 the avicelase activity did not increase until early stationary phase. Total CMCase activity in C. thermocellum was significantly higher than in the three isolates; however, avicelase activities were much more comparable among the four organisms. C. thermocellum produced higher levels of ethanol, and all four organisms produced similar concentrations of acetate. The amounts of free and bound CMCase and avicelase activities were investigated. In C. thermocellum and TP8 most of the CMCase and avicelase activities were bound to the cellulose in the medium. In contrast, most of the CMCase activity in TP1l and KT8 was free in the culture supernatant; a significant percentage of avicelase activity was also free. The TP8 isolate was also grown on a defined medium with urea as sole nitrogen source and cellulose serving as the carbon source. Under these conditions the pattern of enzyme production was the same as that in the enriched medium, although the level of that production was considerably reduced.

text: Comparison of cellulolytic activities in Clostridium thermocellum and Three thermophilic, cellulolytic anaerobes Avicelase, carboxymethyl cellulase (CMCase), and β-glucosidase activities have been compared between Clostridium thermocellum and three extremely thermophilic, cellulolytic anaerobes, isolates TP8, TP11, and KT8. The three isolates were all small, gram-negative staining, oval-ended rods which occurred singly and, at exponential phase, in long chains. They were nonflagellated and no spores were visible. The KT8 and TP11 isolates caused clumping of the cellulose during growth. In all four organisms the CMCase activity paralleled cell growth; however, in C. thermocellum and TP8 the avicelase activity did not increase until early stationary phase. Total CMCase activity in C. thermocellum was significantly higher than in the three isolates; however, avicelase activities were much more comparable among the four organisms. C. thermocellum produced higher levels of ethanol, and all four organisms produced similar concentrations of acetate. The amounts of free and bound CMCase and avicelase activities were investigated. In C. thermocellum and TP8 most of the CMCase and avicelase activities were bound to the cellulose in the medium. In contrast, most of the CMCase activity in TP1l and KT8 was free in the culture supernatant; a significant percentage of avicelase activity was also free. The TP8 isolate was also grown on a defined medium with urea as sole nitrogen source and cellulose serving as the carbon source. Under these conditions the pattern of enzyme production was the same as that in the enriched medium, although the level of that production was considerably reduced.

year: 1986

title: Viewing restorative approaches to addressing challenging behaviour of minority ethnic students through a community of practice lens

authors: Wearmouth, Janice

subjects: restorative practice

abstract: The disproportionately high rates of school exclusion and lower levels of academic achievement of students from particular minority ethnic groups have been a focus of investigation in educational research across the world for some time. This articles uses a communities of practice framework to examine how restorative practice can draw on family and community values to support students whose behaviour is unacceptable in schools to recognize their own agency in behaving for good or ill and reintegrate them into the school community. At the same time, it acknowledges hurt that may be done to victims of wrong-doing and emphasizes putting things right between all those affected. The examples here are from Aotearoa New Zealand. They relate to practices influenced by traditional Māori cultural values. However, the principles and process associated with restorative practices that aim to restore harmony between the individual, the victim and the collective rather than to punish and exclude may be relevant within other student groups where high rates of exclusion from school are problematic.

text: Viewing restorative approaches to addressing challenging behaviour of minority ethnic students through a community of practice lens The disproportionately high rates of school exclusion and lower levels of academic achievement of students from particular minority ethnic groups have been a focus of investigation in educational research across the world for some time. This articles uses a communities of practice framework to examine how restorative practice can draw on family and community values to support students whose behaviour is unacceptable in schools to recognize their own agency in behaving for good or ill and reintegrate them into the school community. At the same time, it acknowledges hurt that may be done to victims of wrong-doing and emphasizes putting things right between all those affected. The examples here are from Aotearoa New Zealand. They relate to practices influenced by traditional Māori cultural values. However, the principles and process associated with restorative practices that aim to restore harmony between the individual, the victim and the collective rather than to punish and exclude may be relevant within other student groups where high rates of exclusion from school are problematic.

year: 2012