HIV gp120 binds CD4+ cells within plasma membrane lipid rafts inducing a conformational change in gp120 that exposes its V3 loop that binds to a chemokine co-receptor, also within lipid rafts, and initiates fusion. Glycosphingolipids (GSLs) may also be bound by gp120. Lipid rafts, enriched with GSLs and cholesterol, are required for HIV entry and therefore the binding of gp120 to GSL-containing vesicles has been studied. Most of the GSL-structures were within the theoretical raft fraction on a discontinuous sucrose gradient while gp120 binding occurred outside of this fraction where a minority of structures migrated. Gb3 fatty acid content modulated binding. Gp120 bound preferentially to structures depleted of cholesterol and binding was enhanced by treating gp120 with CD4. Two water-soluble mimics of Gb3 inhibited gp120 binding to the different structures. The results demonstrate that the aglycone modulation of GSLs alters their receptor function and that the soluble mimics inhibit binding.

HIV gp120 binds CD4+ cells within plasma membrane lipid rafts inducing a conformational change in gp120 that exposes its V3 loop that binds to a chemokine co-receptor, also within lipid rafts, and initiates fusion. Glycosphingolipids (GSLs) may also be bound by gp120. Lipid rafts, enriched with GSLs and cholesterol, are required for HIV entry and therefore the binding of gp120 to GSL-containing vesicles has been studied. Most of the GSL-structures were within the theoretical raft fraction on a discontinuous sucrose gradient while gp120 binding occurred outside of this fraction where a minority of structures migrated. Gb3 fatty acid content modulated binding. Gp120 bound preferentially to structures depleted of cholesterol and binding was enhanced by treating gp120 with CD4. Two water-soluble mimics of Gb3 inhibited gp120 binding to the different structures. The results demonstrate that the aglycone modulation of GSLs alters their receptor function and that the soluble mimics inhibit binding.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is prevalent among the elderly population. Aß protein has been heavily implicated in the pathogenesis of AD. This protein in its fibrillar form is a major component in the senile plaques that form on neuronal cellular membranes during the course of AD. Despite substantial efforts the exact mechanism of Aß toxicity towards a cell membrane is not well-understood. The determination of this mechanism, however, is of utmost importance, since the membrane presents the first site of Aß interaction with neurons, which in turn maybe the origin of Aß neurotoxicity. The purpose of this study was to find a lipid composition that can be used as a model of neuronal membrane for subsequent studies of the role of topographical heterogeneity (domain formation) on Aß-membrane interaction as related to AD. The lipids used in the study were 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), cholesterol (Chol), sphingomyelin (SM) and ganglioside GM1 (GM1). These lipids were combined in different proportions and deposited on a mica substrate to form supported monolayers. They were then imaged with an atomic force microscope (AFM) to determine if any of them exhibited domain formation. Three of the studied samples: POPC/POPG/SM 40:40:20 +5%Chol, POPC/SM/Chol 75:20:5 and POPC/SM/GM1/Chol 74:2:1:23 were found to possess interesting topography, rich in structural features: pores and domains. The average height difference between the domain features for each sample was found to be 0.58±015 nm, 0.61±0.12 nm and 0.27±0:07 nm.

Microalgae surpass the lipid productivity of terrestrial plants by several folds. However, due to the high moisture content and rigidity of algal cell walls, extraction of lipids from algae is still a significant technological challenge. In this research, an attempt was made to develop an algal lipid separation process which is energy efficient and effective. Algal related research requires a unique set of knowledge in areas of algae culturing, measuring cell concentration, harvesting, cell rupturing and lipid quantification. The first section of this thesis focuses on the state of the art as well as knowledge gained during preliminary studies. The second section of this thesis focuses on selecting a suitable measurement technique for quantification of algal cell disruption induced by homogenization. The selected method, hemocytometry was used to measure the degree of algal cell disruption induced by homogenization. In the third section, various homogenization treatments were evaluated for determining the fraction of cells disrupted during the homogenization. Finally, lipid extraction efficiency of homogenized algae was evaluated using different extraction solvents under different homogenization conditions. Preliminary research concluded that using cell counting is the most suitable technique to measure the effect of high pressure homogenization on concentrated microalgae. It was observed that higher pressure and increased number of passes increase the degree of cell disruption. Concentrated, non stressed samples show best response to homogenization. Out of the three solvents used for solvent extraction, chloroform gave a higher extraction yield at low intensity homogenizations. However at harsher homogenization levels the advantage of chloroform was not significant. Lipid extraction efficiency increases with increased levels of homogenization. However, a significant increase in lipid yields was not detected beyond 20 000 psi and 2 passes of homogenization treatment.

We hypothesized that supplementing finishing diets with palm oil would elevate Stearoyl-CoA desaturase (SCD) activity in muscle and subcutaneous (s.c.) adipose tissue, promoting adipocyte differentiation and increase monounsaturated fatty acids (MUFA) in beef, particularly oleic acid. Soybean oil supplementation was used as a negative control. Eighteen Angus steers were assigned randomly to three groups of 6 steers and fed a basal diet without additional fat, with 3% palm oil (rich in palmitic acid), or with 3% soybean oil (rich in polyunsaturated fatty acids), top dressed daily. There were no significant differences across treatment in quality grade, REA, 12th rib fat thickness, or yield grade. Palm oil tended to increase marbling score (P = 0.33). Palm oil supplementation decreased the concentration of myristic acid (P = 0.04), and tended to decrease the concentration of t10, c12 CLA (P = 0.07) and 18:3n-3 (P = 0.06) in s.c. adipose tissue while soybean supplementation increased c9, t11 CLA (P = 0.02) and 18:3n-3 (P = 0.03) in muscle. Palm oil supplementation increased both glucose and acetate incorporation into total lipids of s.c. adipose tissue (both P = 0.03). Volume of s.c. adipocytes was greater in cattle supplemented with palm oil than in soybean- supplemented cattle (P = 0.004). Enzyme activity of G-6-PDH tended to be greater in steers consuming palm oil supplement (P = 0.10). We conclude that there was a partial interaction between palm oil supplementation and adipocyte differentiation. Palm oil supplementation increased s.c. adipocyte content without deteriorating meat quality traits and tended to increase marbling.

Many crucial cellular processes take place at the plasma membrane. The latter is a complex, two-dimensional medium exhibiting significant lateral structure. As a result, a number of non-classical processes, including anomalous diffusion, compartimentalisation and fractal kinetics take place at the membrane surface. The evaluation of various hypotheses and theories about the membrane is currently very difficult because no general modelling framework is available. In this thesis, we present a stochastic, spatially explicit Monte Carlo model for the plasma membrane that accounts for illmixedness, mobile lipid microdomains, fixed proteins, cytoskeletal fence structures and other interactions. We interrogate this model to obtain three classes of results, regarding (1) the effect of lipid microdomains on protein dynamics on the membrane (2) the effects of microdomains, cytoskeletal fences and fixed proteins on the nature of the (anomalous) diffusion on the membrane and (3) the effects of obstructed diffusion on reaction kinetics at the membrane. We find that the presence of lipid microdomains can lead to nonclassical phenomena such as increased collision rates and differences between long-range and short-range diffusion coefficients. Our results also suggest that experimental techniques measuring long-range diffusion may not be sufficiently discriminating and hence cannot be used to infer quantitative information about the presence and characteristics of microdomains. With regard to anomalous diffusion in particular, we find that to explain this phenomenon at the levels observed in vivo, a number of interactions are required, including (but not necessarily limited to) obstacle-induced diffusion and segregation, or exclusion from microdomains. The effects of these different interactions upon the nature of the diffusion appear to be approximately additive. Finally, we show that a widely used non-spatial method, the Stochastic Simulation Algorithm, can be modified to take into account anomalous diffusion and that this significantly increases its predictive accuracy. The model presented in this thesis is expected to be of future value in evaluating different models of cell surface processes.

v, 189 leaves ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1974) from the Dept. of Agricultural Biochemistry and Soil Science, University of Adelaide

Many crucial cellular processes take place at the plasma membrane. The latter is a complex, two-dimensional medium exhibiting significant lateral structure. As a result, a number of non-classical processes, including anomalous diffusion, compartimentalisation and fractal kinetics take place at the membrane surface. The evaluation of various hypotheses and theories about the membrane is currently very difficult because no general modelling framework is available. In this thesis, we present a stochastic, spatially explicit Monte Carlo model for the plasma membrane that accounts for illmixedness, mobile lipid microdomains, fixed proteins, cytoskeletal fence structures and other interactions. We interrogate this model to obtain three classes of results, regarding (1) the effect of lipid microdomains on protein dynamics on the membrane (2) the effects of microdomains, cytoskeletal fences and fixed proteins on the nature of the (anomalous) diffusion on the membrane and (3) the effects of obstructed diffusion on reaction kinetics at the membrane. We find that the presence of lipid microdomains can lead to nonclassical phenomena such as increased collision rates and differences between long-range and short-range diffusion coefficients. Our results also suggest that experimental techniques measuring long-range diffusion may not be sufficiently discriminating and hence cannot be used to infer quantitative information about the presence and characteristics of microdomains. With regard to anomalous diffusion in particular, we find that to explain this phenomenon at the levels observed in vivo, a number of interactions are required, including (but not necessarily limited to) obstacle-induced diffusion and segregation, or exclusion from microdomains. The effects of these different interactions upon the nature of the diffusion appear to be approximately additive. Finally, we show that a widely used non-spatial method, the Stochastic Simulation Algorithm, can be modified to take into account anomalous diffusion and that this significantly increases its predictive accuracy. The model presented in this thesis is expected to be of future value in evaluating different models of cell surface processes.

Many crucial cellular processes take place at the plasma membrane. The latter is a complex, two-dimensional medium exhibiting significant lateral structure. As a result, a number of non-classical processes, including anomalous diffusion, compartimentalisation and fractal kinetics take place at the membrane surface. The evaluation of various hypotheses and theories about the membrane is currently very difficult because no general modelling framework is available. In this thesis, we present a stochastic, spatially explicit Monte Carlo model for the plasma membrane that accounts for illmixedness, mobile lipid microdomains, fixed proteins, cytoskeletal fence structures and other interactions. We interrogate this model to obtain three classes of results, regarding (1) the effect of lipid microdomains on protein dynamics on the membrane (2) the effects of microdomains, cytoskeletal fences and fixed proteins on the nature of the (anomalous) diffusion on the membrane and (3) the effects of obstructed diffusion on reaction kinetics at the membrane. We find that the presence of lipid microdomains can lead to nonclassical phenomena such as increased collision rates and differences between long-range and short-range diffusion coefficients. Our results also suggest that experimental techniques measuring long-range diffusion may not be sufficiently discriminating and hence cannot be used to infer quantitative information about the presence and characteristics of microdomains. With regard to anomalous diffusion in particular, we find that to explain this phenomenon at the levels observed in vivo, a number of interactions are required, including (but not necessarily limited to) obstacle-induced diffusion and segregation, or exclusion from microdomains. The effects of these different interactions upon the nature of the diffusion appear to be approximately additive. Finally, we show that a widely used non-spatial method, the Stochastic Simulation Algorithm, can be modified to take into account anomalous diffusion and that this significantly increases its predictive accuracy. The model presented in this thesis is expected to be of future value in evaluating different models of cell surface processes.

Many crucial cellular processes take place at the plasma membrane. The latter is a complex, two-dimensional medium exhibiting significant lateral structure. As a result, a number of non-classical processes, including anomalous diffusion, compartimentalisation and fractal kinetics take place at the membrane surface. The evaluation of various hypotheses and theories about the membrane is currently very difficult because no general modelling framework is available. In this thesis, we present a stochastic, spatially explicit Monte Carlo model for the plasma membrane that accounts for illmixedness, mobile lipid microdomains, fixed proteins, cytoskeletal fence structures and other interactions. We interrogate this model to obtain three classes of results, regarding (1) the effect of lipid microdomains on protein dynamics on the membrane (2) the effects of microdomains, cytoskeletal fences and fixed proteins on the nature of the (anomalous) diffusion on the membrane and (3) the effects of obstructed diffusion on reaction kinetics at the membrane. We find that the presence of lipid microdomains can lead to nonclassical phenomena such as increased collision rates and differences between long-range and short-range diffusion coefficients. Our results also suggest that experimental techniques measuring long-range diffusion may not be sufficiently discriminating and hence cannot be used to infer quantitative information about the presence and characteristics of microdomains. With regard to anomalous diffusion in particular, we find that to explain this phenomenon at the levels observed in vivo, a number of interactions are required, including (but not necessarily limited to) obstacle-induced diffusion and segregation, or exclusion from microdomains. The effects of these different interactions upon the nature of the diffusion appear to be approximately additive. Finally, we show that a widely used non-spatial method, the Stochastic Simulation Algorithm, can be modified to take into account anomalous diffusion and that this significantly increases its predictive accuracy. The model presented in this thesis is expected to be of future value in evaluating different models of cell surface processes.