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PubMed1977

Experimental phenylketonuria: metabolic studies in rat liver.

The "in vivo" effects of L-phenylalanine on the gluconeogenic pathway in the liver of fasted rats with experimentally induced phenylketonuria-like characteristics have been investigated. Significant increases of the fructose 6-phosphate, glucose 6-phosphate and glucose concentrations were observed. The study of the effect of L-phenylalanine on the cytoplasmic and mitochondrial redox state and energy charge showed an increase in the mitochondrial NAD+/NADH ratio while the energy charge was virtually unchanged. The effects of phenylalanine and its metabolic derivatives (phenylacetate, phenylethylamine, phenyl-lactate, o-hydroxyphenylacetate and phenylpyruvate) on the activity of lactate dehydrogenase (EC 1.1.1.27), malate dehydrogenase (EC 1.1.1.37) and 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) in rat liver have been also investigated. Phenylpyruvate inhibited the lactate dehydrogenase activity with a Ki of 5.3 mM. Phenylpyruvate also inhibited both the mitochondrial (Ki = 4 mM) and cytoplasmic (Ki = 5 mM) malate dehydrogenase activities. Phenylpyruvate, phenylacetate and o-hydroxyphenylacetate inhibited the 3-hydroxybutyrate dehydrogenase activity with Ki values of 0.7, 6.0 and 9.5 mM respectively.

Animals↗
PubMed1975

Postmorten glycolysis in ground skeletal muscle as influenced by prerigor freezing and subsequent thawing.

Ground bovine longissimus and rabbit white muscles were frozen (-25 degrees C) in the prerigor state and subsequently thawed(+20 degrees C) to determine the combined effect of grinding and freezing on glycolytic metabolites and enzymes. Frozen ground muscle, when compared to unfrozen ground tissue, showed significantly lower hexose monophosphates and significantly greater levels of all metabolites from fructose diphosphate to phosphoenolpyruvate, indicating activation of phosphofructokinase and inhibition of pyruvate kinase during the freezing process. Thawing caused rapid glycolysis and the metabolites returned to near unfrozen levels by the time glycolysis ceased, due to strong activation of phosphorylase by Ca2+. Both muscle types had a similar pattern of changes.

Animals↗
PubMed1978

[Contents of glycogen, glycolytic activity and contents of metabolites in the atrioventricular system of bovine hearts (author's transl)].

In the atrioventricular system (AVS) consisting of the compact node, the penetrating bundle and the branching bundles of about 250 bovine hearts there were made several studies: 1. In quickly removed and fixed specimens (distal AV-node, penetrating bundle) determination of a metabolic state with respect to glycogen, glucose, lactate, ATP, ADP, AMP, creatinephosphate, total creatine, gluc-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, dihydroxyacetonphosphate and pyruvate. 2. Determination of glycogen contents and glygolytic activity in AVS and its parts for ischemic times up to three hours. 3. The determination of metabolic contents in samples of connective tissue in atrium and ventricle of bovine hearts. The AV-nodes are poor in glycogen comparable with glycogen content of central nervous system and other ganglia. Penetrating bundles of Hiss and branching bundle belong after liver to the glycogen richest parenchyma of animal tissues. Even after ischemia of 3 h only a part of glycogen was recovered as lactate. The greater part of glycogen must be considered as a structural element of Hiss bundle and branching bundles of the ventricles.

Adenosine Diphosphate↗
PubMedDate not supplied

Metabolism and fine structure of the Mg++-procaine-arrested perfused heart.

Arrested rabbit hearts were perfused in normothermia for up to two hours by a cardioplegic erythrocyte-containing solution having an increased Mg++-, procaine-, and a reduced NaCl-content. After this time, hearts did not reveal any sign of anoxic or toxic damage in their metabolic pattern, in their ultrastructural picture, and in their functional capacity after reanimation. Despite a small loss in adenine nucleotide content, the ATP/ADP ratio and the PC content were raised. The contents of glycogen and glycolytic intermediates were normal or slightly reduced. After two hours of perfusion mitochondria showed no swelling, their membrane structure was unaltered. The myofibrils were well aggregated. The number of glycogen granules was increased. Hearts were reanimated after two hours of cardioplegia and could be loaded by pressure and volume.

Adenosine Diphosphate↗
PubMed1977

Coupling of fructose-1,6-P2 to aminated agarose by Schiff base reduction. Affinity chromatography of yeast aldolase.

Fructose-1,6-P2 was immobilized by sodium borohydride reduction of the Schiff base formed with aminated agarose (AH-Sepharose 4B). The coupling occurs with high yield (25 mumoles immobilized fructose-1,6-P2 per ml packed gel) at neutral pH and room temperature. Schiff base reduction thus provides a convenient and mild coupling prodecure for sugar phosphates preserving their labile phospho ester bonds. As exemplified by a new isolation procedure for fructose-1,6-P2 aldolase from yeast, sugar phosphates insolubilized in this manner may be used for affinity chromatography of the corresponding enzymes, provided that contaminating unspecific phosphatases are removed in a preceding fractionation step.

Chemical Phenomena↗
PubMed1976

Studies on the influence of leucomycine on the carbohydrate metabolism of the lens in vitro.

The influence of leucomycine (10(-5) M--5 X 10(-3) M) on enzyme activities, free adenine nucleotides, and some intermediates of glycolysis in bovine lenses has been investigated. After a 48 h incubation in TCM 199, 6 out of 9 enzymes activities tested were decreased. Concentrations of energy rich nucleotifes, glucose, fructose, and fructose-6-phosphate as well as those of fructose-1,6-diphosphate and lactate were also decreased, whereas adenine monophosphate was increased.

Adenosine Monophosphate↗
PubMed2006

Tissue-culture-responsive and autotetraploidy-responsive changes in metabolic profiles of cucumber (Cucumis sativus L.).

Somaclonal variation commonly occurs during in vitro plant regeneration and may introduce unintended changes in numerous plant characters. In order to assess the range of tissue-culture-responsive changes on the biochemical level, the metabolic profiles of diploid and tetraploid cucumber R1 plants regenerated from leaf-derived callus were determined. Gas chromatography and mass spectrometry were used for monitoring of 48 metabolites and many significant changes were found in metabolic profiles of these plants as compared to a seed-derived control. Most of the changes were common to diploids and tetraploids and were effects of tissue culture. However, tetraploids showed quantitative changes in 14 metabolites, as compared to regenerated diploids. These changes include increases in serine, glucose-6P, fructose-6P, oleic acid and shikimic acid levels. Basing on this study we conclude that the variation in metabolic profiles does not correlate directly with the range of genome changes in tetraploids.

Cucumis sativus↗
PubMed1997

Catabolite regulation of two Escherichia coli operons encoding nitrite reductases: role of the Cra protein.

The Escherichia coli nir and nrf operons, which encode alternative nitrite reductases expressed during anaerobic growth, are subject to catabolite regulation. Transcription from the nir promoter is maximal when bacteria are grown in rich media such as Lennox broth supplemented with glucose. Conversely, expression of the nrf operon is suppressed by rich media, but stimulated during growth in minimal medium with glycerol and fumarate. The role of the catabolite repressor-activator (Cra) protein in catabolite regulation of the nir and nrf promoters was investigated. Transcription from the nir promoter was repressed by Cra when cells were grown in minimal medium with glycerol and fumarate. Crude protein extracts from a strain overproducing Cra encoded on a multicopy plasmid retarded a nir promoter fragment in a mobility shift assay, confirming that the observed Cra-dependent repression was due to the direct interaction of Cra with the regulatory region of the nir operon. Furthermore, the inclusion of fructose 1-phosphate, an effector of Cra DNA-binding activity, in the assay decreased the ability of Cra to retard the nir promoter fragment. In contrast, transcription from the nrf promoter was not regulated by Cra under any of the growth conditions tested.

Bacterial Proteins↗
PubMed1997

Local and global bifurcations at infinity in models of glycolytic oscillations.

We investigate two models of glycolytic oscillations. Each model consists of two coupled nonlinear ordinary differential equations. Both models are found to have a saddle point at infinity and to exhibit a saddle-node bifurcation at infinity, giving rise to a second saddle and a stable node at infinity. Depending on model parameters, a stable limit cycle may blow up to infinite period and amplitude and disappear in the bifurcation, and after the bifurcation, the stable node at infinity then attracts all trajectories. Alternatively, the stable node at infinity may coexist with either a stable sink (not at infinity) or a stable limit cycle. This limit cycle may then disappear in a heteroclinic bifurcation at infinity in which the unstable manifold from one saddle at infinity joins the stable manifold of the other saddle at infinity. These results explain prior reports for one of the models concerning parameter values for which the system does not admit any physical (bounded) behavior. Analytic results on the scaling of amplitude and period close to the bifurcations are obtained and confirmed by numerical computations. Finally, we consider more realistic modified models where all solutions are bounded and show that some of the features stemming from the bifurcations at infinity are still present.

Adenosine Diphosphate↗
PubMed2000

A role of PKC in the improvement of energy metabolism in preconditioned heart.

OBJECTIVE: A possible link between activation of PKC and improvement of energy metabolism during reperfusion in ischemic preconditioning hearts was examined. METHODS: Isolated perfused rat hearts were preconditioned by 5-min ischemia and 5-min reperfusion in the presence and absence of a PKC inhibitor polymyxin B (50 microM) and then subjected to 40-min sustained ischemia and subsequent 30-min reperfusion. In another set of experiments, the hearts pretreated with and without a PKC activator PMA (15 pmol/5 min) were subjected to the sustained ischemia and reperfusion. Myocardial high-energy phosphates, glycolytic intermediates and mitochondrial oxygen consumption capacity were determined at appropriate experimental sequences. RESULTS: Preconditioning enhanced the recovery of cardiac function such as left ventricular developed pressure, heart rate and rate-pressure product of the reperfused heart, suppressed the release of creatine kinase, enhanced the reperfusion-induced restoration of myocardial high-energy phosphates, attenuated the reperfusion-induced accumulation in glucose 6-phosphate and fructose 6-phosphate contents, abolished the ischemia-induced increase in tissue lactate content and prevented the ischemia-induced decrease in mitochondrial oxygen consumption capacity. Treatment of the perfused heart with PMA mimicked the effects of preconditioning on post-ischemic contractile function, enzyme release, levels of myocardial energy store, glycolytic intermediates and lactate, and mitochondrial function. Polymyxin B-treatment abolished the preconditioning-induced recovery of post-ischemic contractile function, the suppression of the release of CK, the restoration of myocardial energy store, and the preservation of mitochondrial function, whereas it did not cancel the improvement of glycolytic intermediate levels and the reduction in tissue lactate accumulation. Post-ischemic contractile function was closely related to restoration of high-energy phosphates and mitochondrial oxygen consumption capacity in all hearts subjected to ischemia/reperfusion. CONCLUSION: The results suggest that activation of PKC and preservation of mitochondrial function are closely linked with each other in the preconditioned heart, which may lead to the improvement of post-ischemic contractile function.

Animals↗
PubMed2002

Regulation of sucrose and starch synthesis in wheat (Triticum aestivum L.) leaves: role of fructose 2,6-bisphosphate.

Fructose 2,6-bisphosphate (F26BP) is a competitive inhibitor of the cytosolic fructose 1,6-bisphosphatase (cytFBPase, EC 3.1.3.11). In spinach (Spinacia oleracea L.) leaves it is a significant component of the complex regulatory network that co-ordinates rates of photosynthesis, sucrose synthesis and starch synthesis. However the role of F26BP has only been studied in plants that predominantly store starch in their leaves and its role in other species is not clear. This paper examines the significance of F26BP in the regulation of photosynthetic carbon metabolism in the intact leaves of wheat (Triticum aestivum L.), a plant that accumulates predominantly sucrose. The approach taken was to vary rates of photosynthesis and then correlate measurements of F26BP and a range of other metabolites with rates of carbohydrate synthesis obtained from (14)CO(2)-feeding experiments performed under physiological conditions. It was found that: (i) Amounts of 3-phosphoglycerate and fructose-6-phosphate are correlated with the amount of F26BP. (ii) F26BP is involved in inhibiting cytFBPase at low light and low CO(2), but other factors, for example triose-phosphate, must also be involved. (iii) Amounts of both F26BP and substrate are involved in co-ordinating rates of photosynthesis and sucrose synthesis, but the relative importance of these depends on the conditions. (iv) Amounts of F26BP do not correlate with the partitioning of fixed carbon between sucrose and starch. Together these data suggest that the amount of F26BP in wheat is regulated by mechanisms similar to those in spinach, and that the metabolite is one of the factors involved in co-ordinating sucrose synthesis and photosynthesis. However F26BP does not appear to be involved in regulating the partitioning of fixed carbon between sucrose and starch in wheat under the experimental conditions examined.

Carbon Dioxide↗