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At least 703 records · Page 39Linked to original sources
PubMed2006

The plant-like C2 glycolate cycle and the bacterial-like glycerate pathway cooperate in phosphoglycolate metabolism in cyanobacteria.

The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO(2)-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO(2). Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO(2). These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO(2), glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.

Alcohol Oxidoreductases↗
PubMed1987

Red cell 3-phosphoglycerate level as a diagnostic aid in pyruvate kinase deficiency.

A case of pyruvate kinase (PK) deficiency is described in which the diagnosis was aided by measurement of the 3-phosphoglycerate (3PG) concentration. Review of the literature on the levels of red cell metabolites in 52 families with PK deficiency confirmed that a rise in 3PG is a valuable indicator of a functional deficiency of PK. Estimation of 3PG is relatively easy (and accurate). Furthermore, reticulocytosis, which sometimes makes the diagnosis of PK deficiency more difficult, has minimal effect on the level of 3PG in comparison with all other glycolytic intermediates or PK activity.

Blood Cell Count↗
PubMed1984

Adenine nucleotides affect the binding of 3-phosphoglycerate to pig muscle 3-phosphoglycerate kinase.

Pig muscle 3-phosphoglycerate kinase was complexed with 1-anilino-8-naphthalenesulfonate (ANS) in order to monitor the binding of substrates to the enzyme. The enzyme-dye interaction did not influence the enzymic activity under the experimental conditions used. By measuring the substrate-dependent change in the fluorescence emission of ANS molecules tightly bound to the enzyme (Kd less than or equal to 0.05 mM), fluorimetric titrations were carried out in 0.1 M Tris/HCl buffer pH 7.5, containing 5 mM mercaptoethanol, at 20 degrees C. The dissociation constants obtained for the separate bindings of 3-phosphoglycerate, MgATP, 1,3-bisphosphoglycerate and MgADP were 0.03 +/- 0.01 mM, 0.15 +/- 0.10 mM, 0.00005 +/- 0.00001 mM and 0.15 +/- 0.10 mM respectively. binding of 3-phosphoglycerate is weakened when MgATP is also bound to the enzyme: the dissociation constant of 3-phosphoglycerate in this ternary complex (0.25 +/- 0.08 mM) is comparable to its Km value (0.38 +/- 0.10 mM). The same weakening can be observed in the non-productive ternary complexes where MgATP is replaced by MgADP (Kd = 0.20 +/- 0.10 mM) or AMP (Kd = 0.12 +/- 0.05 mM), whereas adenosine has no such effect. This indicates the importance of the negatively charged phosphate(s) of nucleotides in influencing the binding of 3-phosphoglycerate. In contrast to 3-phosphoglycerate, the binding of the substrate analogue, glycerol 3-phosphate is practically not affected by the presence of MgATP: the dissociation constant to the free enzyme (0.40 +/- 0.10 mM) is comparable to its inhibitory constant (0.70 +/- 0.20 mM). This finding and the similarity of the dissociation constant of glycerol 3-phosphate binding (0.40 +/- 0.10 mM) and the Km value of 3-phosphoglycerate (0.38 +/- 0.10 mM) suggest that, during the enzymic reaction, binding of 3-phosphoglycerate occurs probably without involvement of the carboxyl group.

Adenine Nucleotides↗
PubMed1984

Increased stability and antiviral activity of 2'-O-phosphoglyceryl derivatives of (2'-5')oligo(adenylate).

Metabolically stable analogues of (2'-5')oligo(adenylate), (2'-5')(A)n, might constitute a new class of antiviral agents as they mimic some of the effects of interferons. 2'-O-phosphoglyceryl derivatives of (2'-5')(A)n oligomers, (2'-5')(A)n-PGro have been synthesized by chemical modification of their terminal ribose residue. Such analogues are resistant to degradation by phosphodiesterases but remain sensitive to phosphatase activity, at least in cell-free extracts. In line with its increased stability, (2'-5')(A)n-PGro has a powerful antiviral activity against an RNA virus when microinjected with micropipettes into the cytoplasm of intact cells. This antiviral activity remains transient however, possibly as a consequence of degradation in intact cells. Since (2'-5')(A)n and its derivatives do not easily cross cell membranes, their possible use in antiviral chemotherapy is tightly linked with the development of vectors suitable for their administration in vivo.

Adenine Nucleotides↗
PubMed1984

Regulation of fructose 2,6-bisphosphate concentration in spinach leaves.

Fructose-6-phosphate 2-kinase and fructose-2,6-bisphosphatase have been partially purified from spinach leaves and their regulatory properties studied. Fructose-6-phosphate 2-kinase was activated by phosphate and fructose 6-phosphate, and inhibited by 3-phosphoglycerate and dihydroxyacetone phosphate. Fructose-2,6-bisphosphatase was inhibited by fructose 6-phosphate and phosphate. The interaction between these effectors was studied when they were varied, alone or in combination, over a range of concentrations representative of those in the cytosol of spinach leaf cells. In conditions when dihydroxyacetone phosphate or 3-phosphoglycerate rise, as is typical during photosynthesis, the fructose 2,6-bisphosphate level will decrease, which will favour sucrose synthesis. In conditions when fructose 6-phosphate accumulates, fructose 2,6-bisphosphate should rise, which will favour a restriction of sucrose synthesis and promotion of starch synthesis.

Cytosol↗
PubMed1988

Effects of metabolite binding to ribulosebisphosphate carboxylase on the activity of the Calvin photosynthesis cycle.

1. The regulatory implications of the interaction of ribulosebisphosphate carboxylase with metabolites participating in the Calvin photosynthesis cycle has been examined by control analysis based on our recently described kinetic model for photosynthetic carbohydrate formation in the chloroplast of C3 plants. The results provide clear evidence that the Calvin cycle activity under conditions of light and CO2 saturation is insignificantly affected by the inhibition of ribulosebisphosphate carboxylase caused by metabolites such as 3-phosphoglycerate, fructose 1,6-bisphosphate, sedoheptulose 1,7-bisphosphate, NADPH, and inorganic orthophosphate. 2. Due to the exceptionally high stromal concentration of the carboxylase, metabolite binding to the enzyme affects the Calvin cycle activity indirectly by reducing the pool of free orthophosphate and phosphorylated metabolites available for the cyclic reactions. This pool reduction corresponds typically to about 5 mM total phosphate and derives mainly from the binding of ribulose bisphosphate and orthophosphate. 3. Substantial amounts of the metabolites interacting with ribulosebisphosphate carboxylase are present in an enzyme-bound form. The bound form of the Calvin cycle intermediates sedoheptulose bisphosphate, fructose bisphosphate, and ribulose bisphosphate typically accounts for about 70, 80, and 90%, respectively, of the total stromal concentration of the intermediate.

Carbohydrate Metabolism↗
PubMed1989

On the regulatory significance of inhibitors acting on non-equilibrium enzymes in the Calvin photosynthesis cycle.

Control analyses and kinetic model studies have been performed in order to obtain quantitative information on the regulatory significance of 12 experimentally well-documented inhibitory interactions of Calvin cycle intermediates with the four non-equilibrium cycle enzymes. Evidence is presented to show that none of these interactions contributes significantly to the cycle flux control over the range of external orthophosphate concentrations where the reaction cycle shows close to optimal activity. Contrary to what has been generally supposed, the examined inhibitions appear to be of little interest for our understanding of the biological regulation of the Calvin photosynthesis cycle under conditions of light and carbon dioxide saturation.

Carbon Dioxide↗