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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activity of enzymes involved in glycolysis, gluconeogenesis, and lipoenesis in early and term human placenta was determined. A high activity of pyruvate kinase was found, indicating high glycolytic potential. The activity of this enzyme tended to decrease with gestation. The presence of phosphoenolpyruvate carboxylase activity was detected, suggesting the possibility of gluconeogenesis in the placenta. Very low activity of enzymes involved in fatty acid synthesis was found, whereas the activity of the pentose shunt pathway enzymes, glucose-6-phosphogluconate dehydrogenases, was relatively high. This suggested a role of this pathway in the synthesis of lipids other than fatty acids in the placenta. The activities of enzymes in the human placenta and their changes during gestation where compared to previous observations on enzymes in rat placenta.
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PMID:Enzymes of glucose and fatty acid metabolism in early and term human placenta. 23 82

The metabolic pathways for the interconversion of oxalacetate, phosphoenolpyruvate, and pyruvate in Pseudomonas citronellolis form an interlocking system (Scheme 1) that would appear to require complex regulatory mechanisms to permit a proper flow of metabolites through the pathways and to prevent futile cycling. Oxalacetate decarboxylase (I in Scheme 1), P-enolpyruvate synthase (II), P-enolpyruvate carboxylase (III), and pyruvate kinase (V) are constitutive enzymes in this organism. Pyruvate carboxylase (VI) is inducible and has its highest activity in cells grown on glucose or lactate, moderate activity in cells grown on acetate, citrate, or glutamate, and virtually no activity in aspartate-grown cells. P-enolpyruvate carboxykinase (IV) was not detected. The presence of these five enzymes in a single cell has not been previously reported. In Scheme 1, three futile cycles are possible: the simultaneous operation of Reactions I and VI; of Reactions II and V; or of I, II, and III. An examination of the regulatory properties of the individual enzymes after partial purification offers support for the hypothesis of an intricate regulatory system. Oxalacetate decarboxylase (I) is inhibited by acetyl-CoA; phosphoenolpyruvate carboxylase (III) is activated by acetyl-CoA and ADP and inhibited by aspartate; phosphoenolpyruvate synthase (II) is inhibited by 5'-AMP and phosphoenolpyruvate; and pyruvate kinase (V) is activated by 5'-AMP and 2 keto, 3-deoxy,6-phosphogluconate and inhibited by ATP. The presence of metabolites with reciprocal but reinforcing functions is noteworthy. As an example, acetyl-CoA both inhibits the breakdown of oxalacetate and stimulates its formation. Only pyruvate carboxylase appears to be regulated by the carbon substrates of the growth medium.
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PMID:Novel enzymic machinery for the metabolism of oxalacetate, phosphoenolpyruvate, and pyruvate in Pseudomonas citronellolis. 83 16

Various concentrations of 6-phosphogluconate inhibit rat liver phosphoenolpyruvate carboxykinase activity. 0.04 mM 6-phosphogluconate, which is the concentration found in vivo, caused a 50% inhibition of 6-phosphoenolpyruvate carboxykinase activity. 6-Phosphogluconate lowered the Vmax of the enzyme and increased the concentration of phosphoenolpyruvate required to achieve one-half of the maximum velocity. The role of 6-phosphogluconate as a regulator of the coordination of fluxes through three metabolic pathways is discussed.
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PMID:Inhibition of phosphoenolpyruvate carboxykinase by 6-phosphogluconate in rat liver. 200 32

The gram-positive bacterium Corynebacterium glutamicum is used for the industrial production of amino acids, e.g. of L-glutamate and L-lysine. During the last 15 years, genetic engineering and amplification of genes have become fascinating methods for studying metabolic pathways in greater detail and for the construction of strains with the desired genotypes. In order to obtain a better understanding of the central metabolism and to quantify the in vivo fluxes in C. glutamicum, the [13C]-labelling technique was combined with metabolite balancing to achieve a unifying comprehensive pathway analysis. These methods can determine the flux distribution at the branch point between glycolysis and the pentose phosphate pathway. The in vivo fluxes in the oxidative part of the pentose phosphate pathway calculated on the basis of intracellular metabolite concentrations and the kinetic constants of the purified glucose-6-phosphate and 6-phosphogluconate dehydrogenases determined in vitro were in full accordance with the fluxes measured by the [13C]-labelling technique. These data indicate that the oxidative pentose phosphate pathway in C. glutamicum is mainly regulated by the ratio of NADPH/NADP concentrations and the specific activity of glucose-6-phosphate dehydrogenase. The carbon flux via the oxidative pentose phosphate pathway correlated with the NADPH demand for L-lysine synthesis. Although it has generally been accepted that phosphoenolpyruvate carboxylase fulfills a main anaplerotic function in C. glutamicum, we recently detected that a biotin-dependent pyruvate carboxylase exists as a further anaplerotic enzyme in this bacterium. In addition to the activities of these two carboxylases three enzymes catalysing the decarboxylation of the C4 metabolites oxaloacetate or malate are also present in this bacterium. The individual flux rates at this complex anaplerotic node were investigated by using [13C]-labelled substrates. The results indicate that both carboxylation and decarboxylation occur simultaneously in C. glutamicum so that a high cyclic flux of oxaloacetate via phosphoenolpyruvate to pyruvate was found. Furthermore, we detected that in C. glutamicum two biosynthetic pathways exist for the synthesis of DL-diaminopimelate and L-lysine. As shown by NMR spectroscopy the relative use of both pathways in vivo is dependent on the ammonium concentration in the culture medium. Mutants defective in one pathway are still able to synthesise enough L-lysine for growth, but the L-lysine yields with overproducers were reduced. The luxury of having these two pathways gives C. glutamicum an increased flexibility in response to changing environmental conditions and is also related to the essential need for DL-diaminopimelate as a building block for the synthesis of the murein sacculus.
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PMID:Pathway analysis and metabolic engineering in Corynebacterium glutamicum. 1107 21

Short-term changes in pyridine nucleotides and other key metabolites were measured during the onset of NO(3) (-) or NH(4) (+) assimilation in the dark by the N-limited green alga Selenastrum minutum. When NH(4) (+) was added to N-limited cells, the NADH/NAD ratio rose immediately and the NADPH/NADP ratio followed more slowly. An immediate decrease in glutamate and 2-oxoglutarate indicates an increased flux through the glutamine synthase/glutamate oxoglutarate aminotransferase. Pyruvate kinase and phosphoenolpyruvate carboxylase are rapidly activated to supply carbon skeletons to the tricarboxylic acid cycle for amino acid synthesis. In contrast, NO(3) (-) addition caused an immediate decrease in the NADPH/NADP ratio that was accompanied by an increase in 6-phosphogluconate and decrease in the glucose-6-phosphate/6-phosphogluconate ratio. These changes show increased glucose-6-phosphate dehydrogenase activity, indicating that the oxidative pentose phosphate pathway supplies some reductant for NO(3) (-) assimilation in the dark. A lag of 30 to 60 seconds in the increase of the NADH/NAD ratio during NO(3) (-) assimilation correlates with a slow activation of pyruvate kinase and phosphoenolpyruvate carboxylase. Together, these results indicate that during NH(4) (+) assimilation, the demand for ATP and carbon skeletons to synthesize amino acid signals activation of respiratory carbon flow. In contrast, during NO(3) (-) assimilation, the initial demand on carbon respiration is for reductant and there is a lag before tricarboxylic acid cycle carbon flow is activated in response to the carbon demands of amino acid synthesis.
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PMID:Activation of Respiration to Support Dark NO(3) and NH(4) Assimilation in the Green Alga Selenastrum minutum. 1666 13