Browsing by Author "Lindsey, George"

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    Changes in leaf hexokinase activity and metabolite levels in response to drying in the desiccation?tolerant species Sporobolus stapfianus and Xerophyta viscosa.
    (Oxford University Press, 2001) Whittaker, Anne; Bochicchio, Adriana; Vazzana, Concetta; Lindsey, George; Farrant, Jill
    The phosphorylation of glucose and fructose is an important step in regulating the supply of hexose sugars for biosynthesis and metabolism. Changes in leaf hexokinase (EC 2.7.1.1) activity and in vivo metabolite levels were examined during drying in desiccation‐tolerant Sporobolus stapfianus and Xerophyta viscosa. Leaf hexokinase activity was significantly induced from 85% to 29% relative water content (RWC) in S. stapfianus and from 89% to 55% RWC in X. viscosa. The increase in hexokinase corresponded to the region of sucrose accumulation in both species, with the highest activity levels coinciding with region of net glucose and fructose removal. The decline of hexose sugars and accumulation of sucrose in both plant species was not associated with a decline in acid and neutral invertase. The increase in hexokinase activity may be important to ensure that the phosphorylation and incorporation of glucose and fructose into metabolism exceeded production from potential hydrolytic activity. Total cellular glucose‐6‐phosphate (Glc‐6‐P) and fructose‐6‐phosphate (Fru‐6‐P) levels were held constant throughout dehydration. In contrast to hexokinase, fructokinase activity was unchanged during dehydration. Hexokinase activity was not fully induced in leaves of S. stapfianus dried detached from the plant, suggesting that the increase in hexokinase may be associated with the acquisition of desiccation‐tolerance.
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    Evaluation of three heterologous xylose isomerase genes for the fermentation of plant biomass to bioethanol in Saccharomyces cerevisiae
    (2008) Robinson, Evan J; Lindsey, George
    Diminishing oil reserves are causing scientists to explore renewable and sustainable replacement fuel sources. One candidate is plant biomass, although without modification its energy-rich sugars remain unavailable to the standard industrial yeast Saccharomyces cerevisiae for fermentation to the fuel ethanol. In this study, three xylose isomerase genes originating from Haemophilus influenzae Rd K20, Arabidopsis thaliana and Bacteroides thetaiotaomicron VPI-5482 were expressed in S. cerevisiae to produce a strain capable of metabolising D-xylose (a biomass constituent). Resulting strains were analysed for protein production, growth differences and xylose isomerisation but no introduced characteristics were detected. RT-PCR suggested transcription occurred for all the genes tested but no recombinant protein nor any xylose isomerase activity was detected. An in silico bioinformatic analysis showed a putative inhibitory stem-loop structure in the mRNA containing the B. thetaiotaomicron gene which may have reduced translation. Otherwise non-functional folding or undetectable activity were concluded as the results of the expression for all genes.
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    The LEA-like protein HSP 12 in Saccharomyces cerevisiae has a plasma membrane location and protects membranes against desiccation and ethanol-induced stress.
    (Elsevier, 2000) Sales, Kurt; Brandt, Wolf; Rumbak, Elaine; Lindsey, George
    The LEA-like protein HSP 12 was identified as having a plasma membrane location in yeast. Gold particles, indicative of the presence of HSP 12, were observed on the external side of the plasma membrane when yeast grown to stationary phase were subjected to immunocytochemical analysis. Growth of yeast in the osmolyte mannitol resulted in an increased number of gold particles that were now observed to be present on both sides of the plasma membrane. No gold particles were observed using a mutant strain of the same yeast that did not express HSP 12. A model liposome system encapsulating the fluorescent dye calcein was used to investigate the protection by HSP 12 of membranes during desiccation. HSP 12 was found to act in an analogous manner to trehalose and protect liposomal membrane integrity against desiccation. The interaction between HSP 12 and the liposomal membrane was judged to be electrostatic as membrane protection was only observed with positively charged liposomes and not with either neutral or negatively charged liposomes. The ability of the wild-type and mutant yeast to grow in media containing ethanol was compared. It was found that yeast not expressing the HSP 12 protein were less able to grow in media containing ethanol. HSP 12 was shown to confer increased integrity on the liposomal membrane in the presence of ethanol. Ethanol, like mannitol, was found to induce HSP 12 protein synthesis. However, yeast grown in both ethanol and mannitol showed a decreased HSP 12 response compared with yeast grown in the presence of either osmolyte alone.
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    Open Access
    Yeast cell wall proteomics: a tale of two proteins.
    (2001) Motshwene, Precious Gugulethu; Lindsey, George; Brandt, Wolf F
    This thesis investigates cell wall proteins, the presence of which increased in concentration as a result of stress. Two such proteins were found, phosphoglycerate mutase and Hsp 12. Studies on these proteins are reported in chapters 2 (phosphoglycerate mutase) and chapter 3 (Hsp 12).