Investigations were carried out on the role of glucagon and calcium in the regulation of hepatic phospholipid biosynthesis. It was found that glucagon inhibits de novo phosphatidylcholine biosynthesis in cultured rat hepatocytes. This inhibition was associated with an inhibition of CTP:phosphochocline cytidylyltransferase activity, which is the regulatory enzyme for phosphatidylcholine biosynthesis. Calcium was shown to inhibit the uptake of choline in hepatocytes by decreasing the Vmax of the saturatable uptake system. It also slightly inhibited the rate of phosphatidylcholine biosynthesis by the de novo pathway, but not by the N-methylation of phosphatidylethanolamine. However, these experiments were difficult to interpret due to the use of ionophore A23187 to vary cytosolic calcium concentrations. This ionophore has many other effects on hepatocytes which could indirectly alter the synthesis of phosphatidylcholine. In vitro studies were carried out to determine the effect of calmodulin on CTP:phosphocholine cytidylyltransferase activity. Although calmodulin did not effect the activity under the conditions of the assay, an impurity of some calmodulin preparations was found which inhibited the cytidylyltransferase in a calcium independent fashion. The inhibitor had some peptide like properties. The effect of calcium on the incorporation of[3- ³H] serine into phospholipids was also investigated. Calcium was found to increase the amount of label recovered in phospholipid. It was also found that,the label was rapidly transfered from phosphatidyserine to phosphatidylethanolamine. On the basis of these results, a model is presented for the relationships between calcium and phosphatidylserine metabolism. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Bibliography: leaves 358-406 / xv, 406 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1985

Offprint of an article by the author inserted / Bibliography: leaves 351-384 / 384 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 1985

A fosfolipase A2 (PLA2) é uma enzima chave no metabolismo dos fosfolípides de membrana e é um dos principais componentes envolvidos na sinalização celular. Alterações da atividade da PLA2 tem sido descritas no cérebro e no sangue (soro, plasma e plaquetas) de pacientes com diversas doenças neuropsiquiátricas. Neste estudo foi desenvolvido um ensaio radioenzimático para detectar em plaquetas, a atividade dos três principais grupos de PLA2, que são PLA2 secretórias ou PLA2 extracelular dependente de Ca 2+ (sPLA2); PLA2 citósólicas dependentes de Ca 2+ (cPLA2) e as PLA2 intracelulares independentes de Ca 2+ (iPLA2). Para confirmar a presença desses grupos da enzima em plaquetas, algumas variáveis foram testadas, como as diferenças de preferência ao ácido graxo como substrato, o requerimento de cálcio e a inibição seletiva com os inibidores Bromoenol lactone (BEL) e o Methyl Arachidonyl Fluorophosphonate (MAFP). Os resultados obtidos demonstram a presença dos três principais grupos de PLA2 (sPLA2, cPLA2, and iPLA2) em plaquetas. Estes achados sugerem o uso de plaquetas, uma amostra biológica de fácil acesso, como possível modelo periférico de neurônios para o estudo do metabolismo de fosfolípides. / Phospholipase A2 (PLA2) is a key-enzyme in the metabolism of membrane phospholipids and is one of the major components involved in cell signaling. Alterations of PLA2 activity have been reported in brains and blood cells in several neuropsychiatric diseases. In this study we developed a radio-enzymatic assay to detect in platelets the activity of the three main groups of PLA2, which are secretory PLA2 or extracellular calcium dependent PLA2 (sPLA2), cytosolic calcium dependent PLA2 (cPLA2) and intracellular calcium independent PLA2 (iPLA2). To confirm the presence of these PLA2 groups some variables were tested, such as differences in the preferred fatty acid substrate, calcium dependence, and selective inhibition with Bromoenol lactone (BEL) and Methyl Arachidonyl Fluorophosphonate (MAFP). Our findings demonstrate the presence of the three main groups of PLA2 (sPLA2, cPLA2, and iPLA2) in platelets. In addition, this study is in line with others suggesting that platelets, a typical biological sample, can be used as a peripheral model for neurons.

A fosfolipase A2 (PLA2) é uma enzima chave no metabolismo dos fosfolípides de membrana e é um dos principais componentes envolvidos na sinalização celular. Alterações da atividade da PLA2 tem sido descritas no cérebro e no sangue (soro, plasma e plaquetas) de pacientes com diversas doenças neuropsiquiátricas. Neste estudo foi desenvolvido um ensaio radioenzimático para detectar em plaquetas, a atividade dos três principais grupos de PLA2, que são PLA2 secretórias ou PLA2 extracelular dependente de Ca 2+ (sPLA2); PLA2 citósólicas dependentes de Ca 2+ (cPLA2) e as PLA2 intracelulares independentes de Ca 2+ (iPLA2). Para confirmar a presença desses grupos da enzima em plaquetas, algumas variáveis foram testadas, como as diferenças de preferência ao ácido graxo como substrato, o requerimento de cálcio e a inibição seletiva com os inibidores Bromoenol lactone (BEL) e o Methyl Arachidonyl Fluorophosphonate (MAFP). Os resultados obtidos demonstram a presença dos três principais grupos de PLA2 (sPLA2, cPLA2, and iPLA2) em plaquetas. Estes achados sugerem o uso de plaquetas, uma amostra biológica de fácil acesso, como possível modelo periférico de neurônios para o estudo do metabolismo de fosfolípides. / Phospholipase A2 (PLA2) is a key-enzyme in the metabolism of membrane phospholipids and is one of the major components involved in cell signaling. Alterations of PLA2 activity have been reported in brains and blood cells in several neuropsychiatric diseases. In this study we developed a radio-enzymatic assay to detect in platelets the activity of the three main groups of PLA2, which are secretory PLA2 or extracellular calcium dependent PLA2 (sPLA2), cytosolic calcium dependent PLA2 (cPLA2) and intracellular calcium independent PLA2 (iPLA2). To confirm the presence of these PLA2 groups some variables were tested, such as differences in the preferred fatty acid substrate, calcium dependence, and selective inhibition with Bromoenol lactone (BEL) and Methyl Arachidonyl Fluorophosphonate (MAFP). Our findings demonstrate the presence of the three main groups of PLA2 (sPLA2, cPLA2, and iPLA2) in platelets. In addition, this study is in line with others suggesting that platelets, a typical biological sample, can be used as a peripheral model for neurons.

Indiana University-Purdue University Indianapolis (IUPUI) / High choline uptake and increased choline kinase activity have been reported in many cancers. This has motivated the use of choline as a biomarker for tumor imaging. Tumors in general are heterogeneous in nature with respect to oxygen tension. There are regions of hypoxia and normoxia that are expected to have different metabolism but regulation of choline metabolism under hypoxia is poorly understood. It is important to clarify the status of choline metabolism in hypoxic microenvironment as it will have an impact on potential of choline as a cancer biomarker. The primary goal was to determine the status of choline phosphorylation in hypoxic cancer cells and its effect on uptake of choline. This was examined by tracer studies in cancer cells exposed to hypoxia. It was observed that hypoxia universally inhibits choline uptake /phosphorylation in cancer cells. Decreased choline phosphorylation resulted in transient uptake of choline radiotracers in cultured cancer cells and 9L tumors suggesting potential problem in using choline as a biomarker for cancers in hypoxic microenvironment. To investigate the mechanism behind decrease in choline phosphorylation, steady state levels of choline metabolites were measured and choline kinase catalyzed choline phosphorylation step was found to be rate-limiting in PC-3 cells. This suggested that modulation in choline kinase levels can alter choline metabolism in hypoxic cancer cells. Expression and activity assays for choline kinase revealed that choline kinase expression is down-regulated in hypoxia. This regulation involved transcriptional level mediation by HIF1 at the conserved HRE7 site in choline kinase promoter. To further understand the importance of down-regulation of choline kinase in hypoxia, stable prostate cancer cell lines over-expressing choline kinase were generated. Effect of over-expression of choline kinase in hypoxia was evaluated in terms of malignant phenotypes like proliferation rate, anchorage independent growth and invasion potential. Both over-expression of choline kinase and hypoxia had a pronounced effect on malignant phenotypes of prostate cancer cells. Further study showed that increased choline kinase activity and hypoxic tumor microenvironment are important for progression of early-stage, androgen-dependent LNCaP prostate cancer cells but confer little survival advantage in undifferentiated, androgen-independent PC-3 prostate cancer cells.

This work expands the knowledge on phospholipid metabolism in the kinetoplastid parasites: T. brucei, T. cruzi, Leishmania spp. that cause neglected tropical diseases and the related non-human pathogenic Crithidia fasiculata. As a close relative of parasitic kinetoplasts, specifically Leishmania, it is hypothesised that Crithidia fasiculata possesses a similar lipid biosynthetic capability and therefore represent an attractive model organism. Database mining the Crithidia genome revealed the ability to biosynthesise all of the main phospholipid species. Utilising various lipidomic techniques, a high level of an ω-6 18:3 fatty acid was observed, alongside an uncommon Δ19:0 fatty acid that was later identified to be exclusive attributed to PE species. Sphingolipid metabolism was shown to resemble that of Leishmania and T. cruzi, given the exclusive production of inositol-phosphoceramide species and no sphingomyelin species being observed. Using labelled precursors, Crithidia were seen to uptake and incorporate extracellular inositol into both phosphatidylinositol and inositol-phosphoceramide species. Crithidia were also shown to utilise both the Kennedy pathway and methylation of phosphatidylethanolamine to form phosphatidylcholine. The phospholipidome of T. cruzi revealed several phosphatidylserine species for the first time, suggesting a functional phosphatidylserine synthase. Current knowledge of T.cruzi sphingolipid biosynthesis was also confirmed as only inositol xxxi phosphoceramide species were observed. The identification and subsequent characterisation of novel phosphonolipid species are reported for the first time. Utilising lipidomic methodologies and labelled precursors, the relative contribution of the intracellular inositol pools within bloodstream and procyclic T. brucei towards PI biosynthesis was examined. This highlighted that the synthesis/turnover rates for specific phosphatidylinositol and inositol-phosphoceramide species are unequal. Efforts to optimise media conditions highlighted that under reduced levels of serum/glucose/inositol, bloodstream T. brucei unexpectedly adjusts its inositol metabolism. The procyclic parasite exemplifies this fact, as under inositol/glucose deficient media conditions they appear to have adapted to utilising glucogenesis and inositol de-novo synthesis. This work highlights that these parasites are rapidly dividing, their unique features of lipid metabolism may be exploitable for drug discovery purposes.