The citrate cleavage enzyme. III. Citryl coenzyme a as a substrate and the stereospecificlty of the enzyme

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Starch-gel electrophoresis of citrate-condensing enzyme from pig heart

Citrate-condensing enzyme from pig heart can exist in vitro as two distinct species which are separable by starch-gel electrophoresis. Several mild types of treatment can interconvert these enzymes and suggest that the separate forms arise in the process of purification; the two enzymes may differ only in the state of reduction of their sulfhydryl groups.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32276/1/0000338.pd

Renal cortical mitochondrial aconitase is regulated in hypo- and hypercitraturia

Renal cortical mitochondrial aconitase is regulated in hypo- and hypercitraturia.BackgroundChronic metabolic acidosis and K+ deficiency increase, while alkali feeding decreases proximal tubule citrate absorption and metabolism. The present studies examined the regulation of mitochondrial aconitase (m-aconitase), the first step in mitochondrial citrate metabolism, in these conditions.MethodsRats were fed appropriate diets, and m-aconitase activity and protein abundance measured.ResultsIn chronic metabolic acidosis and chronic K+ deficiency, renal cortical m-aconitase activity was increased 17% and 43%, respectively. This was associated with respective 90% and 221% increases in renal cortical m-aconitase protein abundance. With chronic alkali feeding, there was a 12% decrease in renal cortical m-aconitase activity, associated with a 35% decrease in m-aconitase protein abundance. Hepatic m-aconitase activity was not regulated in a similar manner. There was no regulation of citrate synthase, the enzyme responsible for mitochondrial citrate synthesis.ConclusionsThese studies demonstrate tissue specific chronic regulation of renal cortical m-aconitase activity and protein abundance, which likely contributes to the hypocitraturia and hypercitraturia seen in these conditions. As m-aconitase is the only step in citrate transport and metabolism found to be regulated in alkali feeding, its regulation likely plays a significant role in mediating the hypercitraturia seen in this condition

Isotope rate effects with D2O in several enzyme systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32361/1/0000433.pd

Patients with chronic fatigue syndrome performed worse than controls in a controlled repeated exercise study despite a normal oxidative phosphorylation capacity

Background: The aim of this study was to investigate the possibility that a decreased mitochondrial ATP synthesis causes muscular and mental fatigue and plays a role in the pathophysiology of the chronic fatigue syndrome (CFS/ME).Methods: Female patients (n = 15) and controls (n = 15) performed a cardiopulmonary exercise test (CPET) by cycling at a continuously increased work rate till maximal exertion. The CPET was repeated 24 h later. Before the tests, blood was taken for the isolation of peripheral blood mononuclear cells (PBMC), which were processed in a special way to preserve their oxidative phosphorylation, which was tested later in the presence of ADP and phosphate in permeabilized cells with glutamate, malate and malonate plus or minus the complex I inhibitor rotenone, and succinate with rotenone plus or minus the complex II inhibitor malonate in order to measure the ATP production via Complex I and II, respectively. Plasma CK was determined as a surrogate measure of a decreased oxidative phosphorylation in muscle, since the previous finding that in a group of patients with external ophthalmoplegia the oxygen consumption by isolated muscle mitochondria correlated negatively with plasma creatine kinase, 24 h after exercise.Results: At both exercise tests the patients reached the anaerobic threshold and the maximal exercise at a much lower oxygen consumption than the controls and this worsened in the second test. This implies an increase of lactate, the product of anaerobic glycolysis, and a decrease of the mitochondrial ATP production in the patients. In the past this was also found in patients with defects in the mitochondrial oxidative phosphorylation. However the oxidative phosphorylation in PBMC was similar in CFS/ME patients and controls. The plasma creatine kinase levels before and 24 h after exercise were low in patients and controls, suggesting normality of the muscular mitochondrial oxidative phosphorylation.Conclusion: The decrease in mitochondrial ATP synthesis in the CFS/ME patients is not caused by a defect in the enzyme complexes catalyzing oxidative phosphorylation, but in another factor

Transketolase catalysed upgrading of l-arabinose: the one-step stereoselective synthesis of l-gluco-heptulose

Conversion of biomass using biocatalysis is likely to become a technology that contributes significantly to the future production of chemical building blocks, materials and transport fuels. Here the synthesis of a value-added chemical from L-arabinose, a major component of the carbohydrates in sugar beet pulp (SBP), in a concise and sustainable manner has been investigated. Biocatalytic conversions using transketolase variants have been developed for the efficient, scalable synthesis of a rare naturally occurring ketoheptose, L-gluco-heptulose, from L-arabinose. New active E. coli TK mutants that readily accept L-arabinose were identified using a versatile colorimetric screening assay and the reaction was performed on a preparative scale

Catabolic enzyme activities in relation to premigratory fattening and muscle hypertrophy in the gray catbird ( Dumetella carolinensis )

The flight muscles of the gray catbird ( Dumetella carolinensis ) were examined to determine if short term adjustments occur in the activity of key catabolic enzymes during preparation for long distance migration. The aerobic capacity of the pectoralis muscle as indicated by citrate synthase activity (CS) is among the highest reported for skeletal muscle (200 μmoles [min·g fresh mass] −1 at 25°C). The mass specific aerobic capacity as indicated by CS activity or cytochrome c concentration does not change during premigratory fattening (Fig. 2) or in relation to the muscle hypertrophy that occurs concomitantly. The maintenance of mass specific aerobic capacity indicates that the total aerobic capacity increases in proportion to the increase in muscle size. The augmented potential for total aerobic power output is considered an adaptation to meet the increased power requirements of flight due to the increased body mass. Additionally, the capacity to oxidize fatty acids, as indicated by β-hydroxyacyl-CoA dehydrogenase activity, approximately doubles during premigratory fattening (from 35 to 70 μmoles [min·g fresh mass] −1 at 25°C; Fig. 1A). This adaptation should favor fatty acid oxidation, thereby sparing carbohydrate and prolonging endurance. The activity of phosphofructokinase, a key glycolytic enzyme, does not change before migration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47125/1/360_2004_Article_BF01101461.pd