title: Solvent dependence of dynamic transitions in protein solutions

authors: Reat, Valerie

subjects: biology

abstract: A transition as a function of increasing temperature from harmonic to anharmonic dynamics has been observed in globular proteins by using spectroscopic, scattering, and computer simulation techniques. We present here results of a dynamic neutron scattering analysis of the solvent dependence of the picosecond-time scale dynamic transition behavior of solutions of a simple single-subunit enzyme, xylanase. The protein is examined in powder form, in D₂O, and in four two-component perdeuterated single-phase cryosolvents in which it is active and stable. The scattering profiles of the mixed solvent systems in the absence of protein are also determined. The general features of the dynamic transition behavior of the protein solutions follow those of the solvents. The dynamic transition in all of the mixed cryosolvent–protein systems is much more gradual than in pure D₂O, consistent with a distribution of energy barriers. The differences between the dynamic behaviors of the various cryosolvent protein solutions themselves are remarkably small. The results are consistent with a picture in which the picosecond-time scale atomic dynamics respond strongly to melting of pure water solvent but are relatively invariant in cryosolvents of differing compositions and melting points.

text: Solvent dependence of dynamic transitions in protein solutions A transition as a function of increasing temperature from harmonic to anharmonic dynamics has been observed in globular proteins by using spectroscopic, scattering, and computer simulation techniques. We present here results of a dynamic neutron scattering analysis of the solvent dependence of the picosecond-time scale dynamic transition behavior of solutions of a simple single-subunit enzyme, xylanase. The protein is examined in powder form, in D₂O, and in four two-component perdeuterated single-phase cryosolvents in which it is active and stable. The scattering profiles of the mixed solvent systems in the absence of protein are also determined. The general features of the dynamic transition behavior of the protein solutions follow those of the solvents. The dynamic transition in all of the mixed cryosolvent–protein systems is much more gradual than in pure D₂O, consistent with a distribution of energy barriers. The differences between the dynamic behaviors of the various cryosolvent protein solutions themselves are remarkably small. The results are consistent with a picture in which the picosecond-time scale atomic dynamics respond strongly to melting of pure water solvent but are relatively invariant in cryosolvents of differing compositions and melting points.

year: 2000

title: Redox cycling of colloidal macro- and micro-nutrients in a monomictic lake

authors: Saeed, Huma

subjects: Anoxia

abstract: Lakes are more than just water bodies as they play an essential role in the cycling of nutrients and carbon, with impacts at the local and global scale. This study selected Lake Ngapouri, a small monomictic lake in the Waikiti Valley, Taupo Volcanic Zone, New Zealand, which receives a considerable amount of nutrients and organic carbon input from the surrounding pastures. The study was designed to investigate the cycling of nutrients and dissolved organic carbon in lake Ngapouri, with a focus on processes occurring at the colloidal size level under varying thermal and redox conditions. 
To achieve the objectives of the study, a year-long sampling campaign was designed involving field and laboratory measurements of the lake's water column. The lake's physicochemical characteristics were determined via high-resolution depth profiles and paried  with a detailed set of depth-resolved geochemical measurements. Analysis for reduced Fe (II) was used to control for oxidative loss during transportation and storage of samples, and generally demonstrated very good protocols and minimal sample alteration. 
This work comprises a comparison of components in colloidal and dissolved size ranges, determined by ultrafiltration under a zero grade N2 atmosphere, and in situ measurements by diffusive gradients in thin films (DGT). Colloids from the lake were additionally analyzed using transmission electron microscopy (TEM), atomic force microscopy (AFM), fluorescence spectroscopy, and a suite of complementary methods. 
Results show considerable changes in the physicochemical properties of the lake over the hydrological year. Isothermal conditions prevailed through the water column during austral autumn and winter, with thermal stratification becoming established as the summer progressed. Dissolved oxygen concentration followed the thermal pattern, and thus vertically divided the water column into three distinct zones during summer. These zones are referred to as 1) Epilimnion (0-5m measuring from the surface) with uniform thermal and dissolved oxygen concentration, 2) transition zone with varying temperature and dissolved oxygen concentration referred to as metalimnion (6-13m), and 3) hypolimnion (15-20m) marked with cold water and reduced oxygen concentration in comparison to the upper two compartments. The pH of the water column stayed circumneutral during this study. The implications of the lake's variation in thermal and redox status on the cycling of macro and micronutrients are discussed in data chapters.  
The third chapter of this thesis addresses the role of suspended iron hydroxides in phosphorus cycling. The spatial and temporal distribution of iron and phosphorus was clearly coupled and was strongly influenced by sediment releases of both elements in anaerobic bed sediments. Both iron and phosphorus were predominantly colloidal and displayed an increasing degree of lability (to DGT) as hypolimnetic anoxia deepened. The implications of this finding are that iron-based colloids can mediate phosphorus cycling even under anaerobic conditions, and might therefore influence iron and phosphorus bioavailability within the water column. 
The fourth chapter of this thesis explores the evolution, seasonal production, and consumption of dissolved organic matter (DOM) in the water column of Lake Ngapouri. Both the quality and quantity of DOM influence the turnover of DOM in the lake system, and this influence was explored using the constituent molecules' fluorescent properties. The resulting excitation-emission matrices (EEM's) were analyzed using parallel factor analysis (PARAFAC), identifying two humic-like fluorophores and one protein-like fluorophore in both colloidal and dissolved size fractions. DOM in the lake showed marked seasonality with greater production and turnover during the summer season. This study shows that the concentration of humic-like DOM was ~3.5 times lower and less variable than protein-like DOM. The proteinaceous material in the low molecular weight fraction cycled actively in the anaerobic hypolimnetic water during summer, consistent with the contemporaneous dissimilatory reduction of manganese, iron, and sulphur. 
Chapter 5 of this thesis examines the spatial and temporal distribution of trace elements (iron (Fe), manganese (Mn), zinc (Zn), copper(Cu), chromium (Cr), cobalt (Co), nickel (Ni), and cadmium (Cd)) in Lake Ngapouri, and the degree to which binding to colloidal surfaces and DOM influence trace element bioavailability. DGT-lability was thus used as a proxy the available metal for biological uptake. In general, the DGT-labile fraction was much lower than a total load of respective trace metal, indicating the significance of adsorption, precipitation, and complexation reactions for trace metal availability for biological uptake. Broadly, the study groups trace metals into two distinct categories: strongly redox cycled, and controlled by organic complexation. This work shows that colloidal association is often, but not always a predictor of lower bioavailability with important implications for our understanding of metal micronutrients in aquatic systems. 
The contributions from this study are significant for studies of the bioavailability of macro and micronutrients which exhibit strong adsorption behavior. The redox state of lakes affects the formation, complexation character, and stability of various mineral colloids. Colloids clearly should be considered as an important intermediary phase with the potential to affect nutrient availability and with implications for lake restoration and management initiatives.

text: Redox cycling of colloidal macro- and micro-nutrients in a monomictic lake Lakes are more than just water bodies as they play an essential role in the cycling of nutrients and carbon, with impacts at the local and global scale. This study selected Lake Ngapouri, a small monomictic lake in the Waikiti Valley, Taupo Volcanic Zone, New Zealand, which receives a considerable amount of nutrients and organic carbon input from the surrounding pastures. The study was designed to investigate the cycling of nutrients and dissolved organic carbon in lake Ngapouri, with a focus on processes occurring at the colloidal size level under varying thermal and redox conditions. 
To achieve the objectives of the study, a year-long sampling campaign was designed involving field and laboratory measurements of the lake's water column. The lake's physicochemical characteristics were determined via high-resolution depth profiles and paried  with a detailed set of depth-resolved geochemical measurements. Analysis for reduced Fe (II) was used to control for oxidative loss during transportation and storage of samples, and generally demonstrated very good protocols and minimal sample alteration. 
This work comprises a comparison of components in colloidal and dissolved size ranges, determined by ultrafiltration under a zero grade N2 atmosphere, and in situ measurements by diffusive gradients in thin films (DGT). Colloids from the lake were additionally analyzed using transmission electron microscopy (TEM), atomic force microscopy (AFM), fluorescence spectroscopy, and a suite of complementary methods. 
Results show considerable changes in the physicochemical properties of the lake over the hydrological year. Isothermal conditions prevailed through the water column during austral autumn and winter, with thermal stratification becoming established as the summer progressed. Dissolved oxygen concentration followed the thermal pattern, and thus vertically divided the water column into three distinct zones during summer. These zones are referred to as 1) Epilimnion (0-5m measuring from the surface) with uniform thermal and dissolved oxygen concentration, 2) transition zone with varying temperature and dissolved oxygen concentration referred to as metalimnion (6-13m), and 3) hypolimnion (15-20m) marked with cold water and reduced oxygen concentration in comparison to the upper two compartments. The pH of the water column stayed circumneutral during this study. The implications of the lake's variation in thermal and redox status on the cycling of macro and micronutrients are discussed in data chapters.  
The third chapter of this thesis addresses the role of suspended iron hydroxides in phosphorus cycling. The spatial and temporal distribution of iron and phosphorus was clearly coupled and was strongly influenced by sediment releases of both elements in anaerobic bed sediments. Both iron and phosphorus were predominantly colloidal and displayed an increasing degree of lability (to DGT) as hypolimnetic anoxia deepened. The implications of this finding are that iron-based colloids can mediate phosphorus cycling even under anaerobic conditions, and might therefore influence iron and phosphorus bioavailability within the water column. 
The fourth chapter of this thesis explores the evolution, seasonal production, and consumption of dissolved organic matter (DOM) in the water column of Lake Ngapouri. Both the quality and quantity of DOM influence the turnover of DOM in the lake system, and this influence was explored using the constituent molecules' fluorescent properties. The resulting excitation-emission matrices (EEM's) were analyzed using parallel factor analysis (PARAFAC), identifying two humic-like fluorophores and one protein-like fluorophore in both colloidal and dissolved size fractions. DOM in the lake showed marked seasonality with greater production and turnover during the summer season. This study shows that the concentration of humic-like DOM was ~3.5 times lower and less variable than protein-like DOM. The proteinaceous material in the low molecular weight fraction cycled actively in the anaerobic hypolimnetic water during summer, consistent with the contemporaneous dissimilatory reduction of manganese, iron, and sulphur. 
Chapter 5 of this thesis examines the spatial and temporal distribution of trace elements (iron (Fe), manganese (Mn), zinc (Zn), copper(Cu), chromium (Cr), cobalt (Co), nickel (Ni), and cadmium (Cd)) in Lake Ngapouri, and the degree to which binding to colloidal surfaces and DOM influence trace element bioavailability. DGT-lability was thus used as a proxy the available metal for biological uptake. In general, the DGT-labile fraction was much lower than a total load of respective trace metal, indicating the significance of adsorption, precipitation, and complexation reactions for trace metal availability for biological uptake. Broadly, the study groups trace metals into two distinct categories: strongly redox cycled, and controlled by organic complexation. This work shows that colloidal association is often, but not always a predictor of lower bioavailability with important implications for our understanding of metal micronutrients in aquatic systems. 
The contributions from this study are significant for studies of the bioavailability of macro and micronutrients which exhibit strong adsorption behavior. The redox state of lakes affects the formation, complexation character, and stability of various mineral colloids. Colloids clearly should be considered as an important intermediary phase with the potential to affect nutrient availability and with implications for lake restoration and management initiatives.

year: 2022

title: “Landlords wouldn’t give my application a second look.” Discrimination exacerbates inequalities in access to private rental housing

authors: Terruhn, Jessica

abstract: This report and the key insights are based on findings from a housing survey that was conducted with 800 residents in neighbourhoods in Auckland, Hamilton and Christchurch. 
• Perceptions of unfairness in Aotearoa’s housing sector are widespread. Renters, Māori, younger people and low-income groups as well as residents in neighbourhoods with high levels of housing deprivation are most likely to think that people are treated unfairly when trying to rent or buy a home in Aotearoa. 
• Nearly one in three respondents reported having experienced discrimination when trying to rent or buy a home in Aotearoa. Renters, Māori, younger people and low-income groups as well as residents in neighbourhoods with high levels of housing deprivation are most likely to report experiences of discrimination. 
• Advantage and disadvantage in securing a home are determined by a combination of interlocking factors, including income and employment status, age, family status, and race/ethnicity or skin colour. These patterns suggest widespread experiences of potentially unlawful housing discrimination. 
• People strategically try to avoid and mitigate discrimination. Expectations of being discriminated against and of being advantaged influence where and how home seekers search for housing. This finding signals that experiences of rejection play a role in constraining people’s housing choices. 
• The survey findings suggest that discrimination, as part of tenant selection, contributes to housing precarity and inequalities in access to rental housing. Therefore, this research points to an urgent need to address housing discrimination, especially in the context of high levels of residential mobility among renters and intense competition for rental properties.

text: “Landlords wouldn’t give my application a second look.” Discrimination exacerbates inequalities in access to private rental housing This report and the key insights are based on findings from a housing survey that was conducted with 800 residents in neighbourhoods in Auckland, Hamilton and Christchurch. 
• Perceptions of unfairness in Aotearoa’s housing sector are widespread. Renters, Māori, younger people and low-income groups as well as residents in neighbourhoods with high levels of housing deprivation are most likely to think that people are treated unfairly when trying to rent or buy a home in Aotearoa. 
• Nearly one in three respondents reported having experienced discrimination when trying to rent or buy a home in Aotearoa. Renters, Māori, younger people and low-income groups as well as residents in neighbourhoods with high levels of housing deprivation are most likely to report experiences of discrimination. 
• Advantage and disadvantage in securing a home are determined by a combination of interlocking factors, including income and employment status, age, family status, and race/ethnicity or skin colour. These patterns suggest widespread experiences of potentially unlawful housing discrimination. 
• People strategically try to avoid and mitigate discrimination. Expectations of being discriminated against and of being advantaged influence where and how home seekers search for housing. This finding signals that experiences of rejection play a role in constraining people’s housing choices. 
• The survey findings suggest that discrimination, as part of tenant selection, contributes to housing precarity and inequalities in access to rental housing. Therefore, this research points to an urgent need to address housing discrimination, especially in the context of high levels of residential mobility among renters and intense competition for rental properties.

year: 2024-08