Thesis (M.D. 1974) from the Dept. of Psychiatry, University of Adelaide.

Thesis (Ph. D.)--Michigan State University. Dept. of Biochemistry and Molecular Biology, 2008. / Title from PDF t.p. (viewed on July 10, 2009) Includes bibliographical references. Also issued in print.

Thesis (M.SC.) - Carleton University, 2007. / Includes bibliographical references (p. 101-106). Also available in electronic format on the Internet.

Thesis (M.Med.Sc.)--University of Hong Kong, 1984. / Also available in print.

No description available.

vii, 235 leaves : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D. 1974) from the Dept. of Psychiatry, University of Adelaide

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Phosphoenolpyruvate carboxylase (PEPC) was examined during cold acclimation of seedlings of the freezing-tolerant cultivar (Medicago sativa ssp falcata cv Anik) and the relatively freezing-sensitive cultivar (Medicago sativa cv Trek) of alfalfa. With four days of cold acclimation, PEPC activity increased to 3.5-fold and 2-fold the control levels in Anik and Trek, respectively. This was associated with an increase in the level of a 110 kD PEPC protein and a decrease in the amount of a 120 kD PEPC polypeptide in both cultivars. The role of reversible phosphorylation in regulating PEPC activity was demonstrated by in vitro phosphorylation and dephosphorylation, which caused partial activation and deactivation of PEPC, respectively. In vivo phosphorylation experiments revealed that the 110 kD PEPC subunit is phosphorylated on serine residue(s) during cold acclimation in Anik but not in Trek. Increased PEPC activity could account for the 70% increase in the non-autotrophic or dark fixation of carbon observed in cold acclimated Anik seedlings. A possible role for dark carbon fixation in the cold-induced development of freezing tolerance is through the production of NADPH. Such a source of reducing power may be required for the repair of cold-induced damage and restoration of normal cellular functions.

During the present studies we attempted to answer the following questions: (i) Does low temperature alter the phosphorylation level of proteins in isolated nuclei? (ii) Does the nuclear phosphoprotein population change during a prolonged exposure of seedlings to cold? (iii) Do heat-stable proteins accumulate in the nucleus during a prolonged exposure of seedlings to cold? (iv) Are the answers to the above three questions related to freezing tolerance? A possible relationship between the observed cold-induced changes in phosphoproteins and the level of freezing tolerance was explored by comparing the results of experiments conducted on two cultivars (Apica and Trek) of alfalfa (Medicago sativa L.) which markedly differ in their capacity for cold acclimation. / We show that the phosphorylation level of several nuclear proteins is subject to rapid and reversible enhancement by low temperature. Several phosphoproteins were found to be constitutively present in the nucleus of both cultivars. The cold-induced stimulation of the phosphorylation of many of these proteins was much greater in the relatively freezing tolerant cultivar Apica than in the relatively freezing sensitive cultivar Trek. Population of nuclear phosphoproteins was found to be considerably more complex in Apica than in Trek. During a prolonged exposure of the seedlings to 4$ sp circ$C, additional phosphoproteins were imported into the nucleus of Apica seedlings but not those Trek. / Some heat-stable proteins were constitutively present in the nucleus of both cultivars. However during the 4-day cold treatment, a large accumulation of several additional heat-stable proteins was observed in the tolerant, but not the sensitive, cultivar. (Abstract shortened by UMI.)

The marine bacterium Sphingopyxis alaskensis was isolated as one of the most numerically abundant bacteria from cold (4–10??C) nutrient depleted waters in the North Pacific Ocean. The objective of this study was to examine cold adaptation of S. alaskensis by using proteomics to examine changes in global protein levels caused by growth at low (10??C) and high (30??C) temperatures. Stable isotope labelling-based quantitative proteomics was used, and a rigorous post-experimental data processing workflow adapted from microarray-based methods was developed. The approach included metabolic labelling with 14N/15N and normalisation and statistical testing of quantitative proteomics data. Approximately 400,000 tandem mass spectra were generated resulting in the confident identification of 2,135 proteins (66% genome coverage) and the quantitation of 1,172 proteins (37% genome coverage). Normalisation approaches were evaluated using cultures grown at 30??C and labelled with 14N and 15N. For 10??C vs. 30??C experiments, protein quantities were normalised within each experiment using a multivariate lowess approach. Statistical significance was assessed by combining data from all experiments and applying a moderated t-test using the empirical Bayes method with the limma package in R. Proteins were ranked after calculating the B-statistic and the Storey-Tibshirani false discovery rate. 217 proteins (6% genome coverage) were determined to have significant quantitative differences. In achieving these outcomes a range of factors that impact on quantitative proteomics data quality were broadly assessed, resulting in the development of a robust approach that is generally applicable to quantitative proteomics of biological system. The significantly differentially abundant proteins from the proteomics data provided insight into molecular mechanisms of cold adaptation in S. alaskensis. Important aspects of cold adaptation included cell membrane restructuring, exopolysaccharide biosynthesis, lipid degradation, carbohydrate and amino acid metabolism, and increased capacity of transcriptional and translational processes. A number of cold adaptive responses in S. alaskensis were novel, including a specific cold-active protein folding pathway, a possible thermally-controlled stringent response, and biosynthesis of intracellular polyhydroxyalkanoate reserve material. The overall study provided important new insight into the evolution of growth strategies necessary for the effective competition of S. alaskensis in cold, oligotrophic environments.