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Citric Acid Cycle (citric + acid_cycle)
Selected AbstractsManganese speciation in human cerebrospinal fluid using CZE coupled to inductively coupled plasma MSELECTROPHORESIS, Issue 9 2007Bernhard Michalke Dr. Abstract The neurotoxic effects of manganese (Mn) at elevated concentrations are well known. This raises the question, which of the Mn species can cross neural barriers and appear in cerebrospinal fluid (CSF). CSF is the last matrix in a living human organism available for analysis before a compound reaches the brain cells and therefore it is assumed to reflect best the internal exposure of brain tissue to Mn species. A previously developed CE method was modified for separation of albumin, histidine, tyrosine, cystine, fumarate, malate, inorganic Mn, oxalacetate, ,-keto-glutarate, nicotinamide-dinucleotide (NAD), citrate, adenosine, glutathione, and glutamine. These compounds are supposed in the literature to act as potential Mn carriers. In a first attempt, these compounds were analyzed by CZE-UV to check whether they are present in CSF. The CZE-UV method was simpler than the coupled CZE-inductively coupled plasma (ICP)-dynamic reaction cell (DRC)-MS method and it was therefore chosen to obtain a first overview information. In a second step, the coupled method (CZE-ICP-DRC-MS) was used to analyze, in detail, which of the compounds found in CSF by CZE-UV were actually bound to Mn. Finally, 13 Mn species were monitored in CSF samples, most of them being identified: Mn-histidine, Mn-fumarate, Mn-malate, inorganic Mn, Mn-oxalacetate, Mn-,-keto glutarate, Mn-carrying NAD, Mn-citrate and Mn-adenosine. By far the most abundant Mn species was Mn-citrate showing a concentration of 0.7,±,0.13,µg,Mn/L. Interestingly, several other Mn species can be related to the citric acid cycle. [source] The Alternative Oxidase: in vivo Regulation and FunctionPLANT BIOLOGY, Issue 1 2003F. F. Millenaar Abstract: This review focuses on the biochemical regulation and function of the alternative oxidase in vivo. About 10 years ago, two activation mechanisms were discovered in isolated mitochondria, namely activation by reducing sulfur bonds in the protein and activation by an allosteric effect of pyruvate. It was proposed that plants would have a regulatory mechanism to modify alternative oxidase activity in vivo. However, more recent studies have shown that these two activation mechanisms may not play such an important role in regulation of alternative oxidase activity in vivo after all. Pyruvate and reduction of the sulfide bonds in the protein are definitely required for alternative oxidase activity, but they do not appear to be regulating the activity in vivo. Despite the energy wasting nature of the alternative oxidase, there was no obvious physiological function for the pathway for many years. It is now more clear that the alternative oxidase can prevent the production of excess reactive oxygen species radicals by stabilizing the redox state of the mitochondrial ubiquinone pool, while allowing continued activity of the citric acid cycle. This may be important under conditions when the NADH supply is relatively high (reductant overflow), or when the cytochrome pathway is restrained. The cytochrome pathway might be inhibited by naturally occurring cyanide, nitric oxide, sulfide, high concentrations of CO2, low temperatures, or by limited phosphate supply. [source] Proteomic analysis of hearts from frataxin knockout mice: Marked rearrangement of energy metabolism, a response to cellular stress and altered expression of proteins involved in cell structure, motility and metabolismPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 8 2008Robert Sutak Abstract A frequent cause of death in Friedreich's ataxia patients is cardiomyopathy, but the molecular alterations underlying this condition are unknown. We performed 2-DE to characterize the changes in protein expression of hearts using the muscle creatine kinase frataxin conditional knockout (KO) mouse. Pronounced changes in protein expression profile were observed in 9,week-old KO mice with severe cardiomyopathy. In contrast, only several proteins showed altered expression in asymptomatic 4,week-old KO mice. In hearts from frataxin KO mice, components of the iron-dependent complex-I and -II of the mitochondrial electron transport chain and enzymes involved in ATP homeostasis (creatine kinase, adenylate kinase) displayed decreased expression. Interestingly, the KO hearts exhibited increased expression of enzymes involved in the citric acid cycle, catabolism of branched-chain amino acids, ketone body utilization and pyruvate decarboxylation. This constitutes evidence of metabolic compensation due to decreased expression of electron transport proteins. There was also pronounced up-regulation of proteins involved in stress protection, such as a variety of chaperones, as well as altered expression of proteins involved in cellular structure, motility and general metabolism. This is the first report of the molecular changes at the protein level which could be involved in the cardiomyopathy of the frataxin KO mouse. [source] Purification, crystallization and preliminary X-ray analysis of isocitrate dehydrogenase kinase/phosphatase from Escherichia coliACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2009Jimin Zheng The Escherichia coli aceK gene encodes isocitrate dehydrogenase kinase/phosphatase (EC 2.7.11.5), a bifunctional protein that phosphorylates and dephosphorylates isocitrate dehydrogenase (IDH), resulting in its inactivation and activation, respectively. This reversible (de)phosphorylation directs isocitrate, an intermediate of the citric acid cycle, to either go through the full cycle or to enter the glyoxylate bypass. In the present study, the AceK protein from E. coli has been purified and crystallized. Three crystal forms were obtained from very similar crystallization conditions. The crystals belong to space groups P41212, P3221 and P212121 and diffracted X-rays to resolutions of 2.9, 3.0 and 2.7,Å, respectively. [source] Understanding and Improving NADPH-Dependent Reactions by Nongrowing Escherichia coli CellsBIOTECHNOLOGY PROGRESS, Issue 2 2004Adam Z. Walton We have shown that whole Escherichia coli cells overexpressing NADPH-dependent cyclohexanone monooxygenase carry out a model Baeyer-Villiger oxidation with high volumetric productivity (0.79 g ,-caprolactone/L·h ) under nongrowing conditions (Walton, A. Z.; Stewart, J. D. Biotechnol. Prog.2002, 18, 262,268). This is approximately 20-fold higher than the space-time yield for reactions that used growing cells of the same strain. Here, we show that the intracellular stability of cyclohexanone monooxygenase and the rate of substrate transport across the cell membrane were the key limitations on the overall reaction duration and rate, respectively. Directly measuring the levels of intracellular nicotinamide cofactors under bioprocess conditions suggested that E. coli cells could support even more efficient NADPH-dependent bioconversions if a more suitable enzyme-substrate pair were identified. This was demonstrated by reducing ethyl acetoacetate with whole cells of an E. coli strain that overexpressed an NADPH-dependent, short-chain dehydrogenase from bakerapos;s yeast ( Saccharomyces cerevisiae). Under glucose-fed, nongrowing conditions, this reduction proceeded with a space-time yield of 2.0 g/L·h and a final product titer of 15.8 g/L using a biocatalyst:substrate ratio (g/g) of only 0.37. These values are significantly higher than those obtained previously. Moreover, the stoichiometry linking ketone reduction and glucose consumption (2.3 ± 0.1) suggested that the citric acid cycle supplied the bulk of the intracellular NADPH under our process conditions. This information can be used to improve the efficiency of glucose utilization even further by metabolic engineering strategies that increase carbon flux through the pentose phosphate pathway. [source] | |||||||||||||