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PubMed1988

Metabolism of glucose 1,6-P2--III. Partial purification and characterization of glucose 1,6-P2 synthase from pig skeletal muscle.

1. Glycerate 1,3-P2-dependent glucose, 1,6-P2 synthase has been purified 2000-fold from pig skeletal muscle, with a yield of 75%. 2. The enzyme possesses fructose 1,6-P2-dependent glucose 1,6-P2 synthase and phosphoglucomutase activities, which represent 0.1 and 60% of the main activity, respectively. 3. Both glucose 1-P and glucose 6-P can act as acceptors of the phosphoryl group from glycerate 1,3-P2. 4. The Km values are 19 microM and 67 nM for glucose 1-P and glycerate 1,3-P2, respectively. 5. The enzyme is inhibited by glycerate 2,3-P2, fructose 1,6-P2, glycerate 3-P, phosphoenolpyruvate and lithium, the inhibition pattern varying with the compound.

Animals↗
PubMed1988

2,3-Bisphosphoglycerate inhibits hemoglobin synthesis and phosphorylation of initiation factor 2 by casein kinase II in reticulocyte lysates.

2,3-Bisphosphoglycerate inhibited protein synthesis in reticulocyte lysates with 50% inhibition at 2 mM. Glycerate 2,3-P2 increased the Mg2+ optimum for protein synthesis by chelation of Mg2+, but Mg2+ addition did not completely reverse the inhibition, suggesting an additional site of action. eIF-2 has been used to examine the activity of casein kinase II in reticulocyte lysates in response to glycerate 2,3-P2. When glycerate 2,3-P2 was increased to 4mM, phosphorylation of eIF-2 beta was increasingly inhibited. Thus inhibition of phosphorylation of translational components by casein kinase II can be correlated with inhibition of globin synthesis at physiological concentrations of glycerate 2,3-P2.

2,3-Diphosphoglycerate↗
PubMed1976

Enolase isoenzymes. III. Chromatographic and immunological characteristics of rat brain enolase.

1. The chromatography of rat brain enolase (2-phospho-D-glycerate hydrolyase, EC 4.2.1.11) reveals three distinet components. One of these appears to be isoenzyme 1 (alpha alpha) but isoenzymes 2 (alpha beta) and 3 (beta beta) are absent. 2. The most acidic form of brain enolase was partially purified and an antiserum raised against it in the chicken. 3. a combination of chromatographic and immunological studies showed that a third type of subunit (gamma) is present in the brain giving rise to two further isoenzymes (alpha gamma and gamma gamma). 4. Developmental studies on the brain enzyme show an increase in total enolase activity from foetal life to maturity and a concurrent rise in the proportion of brain specific dimers. 5. It is therefore concluded that there are three genetic loci alpha, beta and gamma, coding for the enolase isoenzymes of rat tissues.

Aging↗
PubMed1991

The novel tungsten-iron-sulfur protein of the hyperthermophilic archaebacterium, Pyrococcus furiosus, is an aldehyde ferredoxin oxidoreductase. Evidence for its participation in a unique glycolytic pathway.

The anaerobic archaebacterium, Pyrococcus furiosus, grows optimally at 100 degrees C by a fermentative-type metabolism in which H2, CO2, and organic acids are end products. The growth of this organism is stimulated by tungsten, and, from it, a novel, red-colored, tungsten-iron-sulfur protein, abbreviated RTP, has been purified (Mukund, S., and Adams, M. W. W. (1990) J. Biol. Chem. 265, 11508-11516). RTP (Mr approximately 85,000) contained approximately 1W, 7Fe, and 5 acid-labile sulfide atoms/molecule and exhibited unique EPR properties. The physiological function of the protein, however, was unknown. We show here that RTP is an inactive form of an aldehyde ferredoxin oxidoreductase (AOR). The active enzyme was obtained by rapid purification under anaerobic conditions using buffers containing dithiothreitol and glycerol. AOR catalyzed the oxidation of a range of aliphatic aldehydes with an optimum temperature for activity above 90 degrees C, but it did not oxidize glucose or glyceraldehyde 3-phosphate, nor reduce NAD(P), and its activity was independent of CoA. The active (AOR) and inactive (RTP) forms of the enzyme were indistinguishable in their contents of metals and acid-labile sulfide and in their EPR properties. The latter are though to originate from two nonidentical and spin-coupled iron-sulfur clusters, whereas the tungsten in this enzyme, which was not detectable by EPR, appears to be present as a novel pterin cofactor. Inhibition and activation studies indicated that AOR contains a catalytically essential W-SH group that is not present in RTP, the inactive form. AOR is a new type of aldehyde-oxidizing enzyme and is the first aldehyde oxidoreductase to be purified from an archaebacterium or a nonactogenic anaerobic bacterium. Its physiological role in P. furiosus is proposed as the oxidation of glyceraldehyde to glycerate in a unique, partially nonphosphorylated, glycolytic pathway that generates acetyl-CoA from glucose without the participation of nicotinamide nucleotides.

Aldehyde Oxidoreductases↗
PubMed1983

Kinetic studies of the reaction mechanism of rat liver phosphoglycerate kinase in the direction of ADP utilization.

The kinetic properties of rat liver phosphoglycerate kinase were investigated in the forward direction of the reaction (utilization of ADP). The kinetic studies were performed in an assay system using combined hexokinase/glucose-6-phosphate dehydrogenase as an ATP trap. The Km values for Mg ADP1- and 1,3-diphospho-D-glycerate were approximately 0.11 and 0.006 mM, respectively. Reciprocal plots of 1/v versus 1/ (Mg ADP1-) at different fixed concentrations of 1,3-diphospho-D-glycerate and 1/v versus 1/ (1,3-diphospho-D-glycerate) at different fixed concentrations of Mg ADP1- were apparently parallel. However, product inhibition studies (3-phospho-D-glycerate), dead-end inhibition studies (2,3-diphospho-D-glycerate), and adenosine and AMP inhibition patterns yielded results consistent with a rapid equilibrium random mechanism in which the binding of one substrate greatly decreases the affinity of the enzyme for the second substrate. Existence of two sites for 3-phospho-D-glycerate is suggested.

2,3-Diphosphoglycerate↗
PubMed1982

Taxonomic survey for the presence of ribulose-1,5-bisphosphate carboxylase activity in guard cells.

Guard cell pairs were dissected from freeze-dried leaves of plants representing 15 families, including monocots, dicots, and pteridophytes. All three major photosynthetic carbon pathways (C(2), C(4), and Crassulacean acid metabolism) were represented. These individual guard cell pairs were assayed quantitatively for ribulose-1,5-bisphosphate carboxylase specific activity. Assay sensitivity averaged 0.08 picomoles of ribulose-P(2) dependent P-glycerate formation (i.e. 100-fold more sensitive than required to detect the activity present in a single Vicia faba mesophyll cell). The calculated specific activities for guard cells and mesophyll cells averaged 4 and 472 millimoles per kilogram dry weight per hour, respectively. For all species surveyed, (a) the enzyme activity calculated for guard cells was below the detection limit of the assay, or (b) the specific activity (weight or cell basis) calculated for guard cells was less than 1% of the specific activity calculated for adjacent mesophyll cells. Based on this survey, the generalization is made that the photosynthetic carbon reduction pathway is absent, or virtually so, in guard cell chloroplasts.

Journal Article↗
PubMed1994

Cloning and expression of the gene for hydroxypyruvate reductase (D-glycerate dehydrogenase from an obligate methylotroph Hyphomicrobium methylovorum GM2.

The gene encoding hydroxypyruvate reductase, catalyzing the asymmetric reduction of hydroxypyruvate to D-glycerate, and its flanking regions were isolated from a methylotrophic bacterium, Hyphomicrobium methylovorum GM2. Nucleotide sequencing of the recombinant plasmids revealed that the hydroxypyruvate-reductase gene codes for the 322-amino-acid protein with calculated molecular mass 35,726 Da. The sequence was confirmed by sequencing the intact enzyme and peptides obtained by digestion of the enzyme with Achromobacter proteinase I. The amino acid sequence of the enzyme showed similarity to members of the D-isomer-specific 2-hydroxyacid dehydrogenase family. The recombinant plasmid, which was constructed by ligation of the cloned gene and an expression vector pKK223-3, was introduced into Escherichia coli HB101. The recombinant enzyme purified from the transformed E. coli cells was indistinguishable from the enzyme isolated from H. methylovorum GM2 by immunological and enzymological analyses.

Alcohol Oxidoreductases↗
PubMed2000

Mass flux balance-based model and metabolic flux analysis for collagen synthesis in the fibrogenesis process of human liver.

A mass flux balance-based stoichiometric model for human liver metabolism has been set up. The model considers 125 reaction fluxes, and there are 83 metabolites that are assumed to be in pseudo-steady state. Theoretical metabolic flux distributions in the fibrotic and healthy liver cells were determined by maximizing respectively the collagen and palmitate synthesis in the objective function for the solution of the model. The flux distribution maps of the analysis for the collagen synthesis showed that the glycolysis pathway was active down to fructose-6-phosphate and the gluconeogenesis pathway was active up to glyceraldehyde 3-phosphate synthesis. However, the flux distribution maps for the palmitate synthesis revealed that both the glycolysis pathway and the gluconeogenesis pathway were active towards 3-phospho glycerate. The TCA cycle operated from citrate towards oxalacetate, and the anaplerotic reactions that connect the TCA cycle to the gluconeogenesis pathway were active in both analyses. Metabolic flux analysis shows that the amino acid fluxes are indeed important in the collagen synthesis. The results of the comparative analyses for the occurrence of the collagen synthesis in the fibrotic liver cells reveal that among the non-essential amino acids three, namely glycine, proline and aspartic acid, and among the essential amino acids one, methionine, are respectively the potential metabolic bottlenecks and the limiting amino acid. The diversions in the pathways and certain metabolic reactions are also presented, and potential strategies for controlling the collagen synthesis and consequently the fibrosis are also discussed.

Amino Acids↗
PubMed1996

Induction of antibodies against SIV antigens after intramuscular nucleic acid inoculation using complex expression constructs.

By studying the infection of rhesus macaques with simian immunodeficiency virus (SIVmac) the potential of nucleic acid immunisation against AIDS can be evaluated. As a first step towards the development of suitable expression constructs, the levels and the durations of expression elicited by the house-keeping gene promoters of the murine phospho-glycerate kinase (PGK) gene and rat proto-ras 1Ha, a lentiviral LTR and the CMV-intron A promoter were tested in BALB/c mice intramuscularly inoculated with marker gene constructs encoding luciferase. The expression levels achieved by the CMV-intron A and the lentiviral promoter were comparably high, and also the PGK promoter induced a high level of expression for at least 64 days. Following the inoculation of plasmids comprising single or multiple genes of SIV, the induction of specific antibodies directed against SIV antigens was demonstrated. We previously showed in vitro that int- and nef-defective mutants of SIVmac were able to initiate a limited and self-abortive infection of permissive cells in the absence of chromosomal integration of the viral DNA. Intramuscular inoculations in monkeys using int-defective proviral DNA of SIV will show whether an increased immune response may be induced by expression of viruses undergoing a self-limited replication in vivo.

Animals↗
PubMed1976

The uptake of 2-ketogluconate by Pseudomonas putida.

The uptake of 2-ketogluconate is inducible in Pseudomonas putida: 2-ketogluconate, glucose, gluconate, glycerol and glycerate were each good nutritional inducers of this ability. 2-Ketogluconate uptake obeyed saturation kinetics (apparent Km in 2-ketogluconate-grown cells was 0.4 mM). 2-Ketogluconate was transported against a concentration gradient, apparently in an unchanged state, and the process required metabolic energy, all of which indicate an active transport system. A number of independently isolated mutants with deranged activity of a common glucose-gluconate uptake system were found to be also defective in 2-ketogluconate transport. Strains unable to transport 2-ketogluconate which grew readily on glucose and gluconate were also isolated. These results suggest that 2-ketogluconate transport is governed by at least two genetic elements: one which is also required to take up glucose and gluconate and another which appears to be specific for 2-ketogluconate transport. Similarly, glucose and gluconate transport appears to require at least one factor which is not necessary for 2-ketogluconate transport, as suggested by the lack of induction of the common glucose-gluconate uptake system by glycerol and glycerate, substrates which are good inducers of 2-ketogluconate uptake.

Biological Transport, Active↗
PubMed1977

Regulation of human erythrocyte hexokinase. The influence of glycolytic intermediates and inorganic phosphate.

Human erythrocyte hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) was inhibited competitively with respect to MgATP2- by glucose-6-P (Ki - 10.8 muM) and fructose-6-P (Ki = 160 muM). Low concentrations of inorganic phosphate were competitive with respect to glucose-6-P and fructose-6-P, although higher concentrations of Pi were not able to overcome completely the inhibition by the hexose phosphates. The results are consistent with a model in which hexokinase exists in equilibrium either as free or phosphate-associated enzyme, the latter having a reduced but still substantial affinity for hexose phosphate. An alternative explanation could be found in the presence of two different enzymes, one with a high affinity for glucose-6-P being sensitive to regulation by Pi, one with a lower affinity for glucose-6-P being insensitive to Pi. A similar but less pronounced effect of Pi, was found on the inhibition by 2,3-diphosphoglycerate (Ki = 4.0 mM). Pi in the absence of inhibitor was also a competitive inhibitor with respect to MgATP2- (Ki = 20 mM). Furthermore a competitive inhibition with respect to MgATP2- was found by fructose 1,6-diphosphate (Ki = 4.3 mM), glycerate-3-P (Ki = 3.8 mM), glycerate-2-P (Ki = 12.5 mM), MgADP- (Ki = 1.0 mM) and MgAMP (Ki = 1.7 mM).

Adenosine Triphosphate↗
PubMed1979

The pH dependence of the binding of D-glycerate 2,3-bisphosphate to deoxyhemoglobin and oxyhemoglobin. Determination of the number of binding sites in oxyhemoglobin.

The number of Bohr protons released upon oxygenation has been measured over a large range of human hemoglobin concentrations (0.02 to 4.5 mM) in the presence of equimolar amounts of D-glycerate 2,3-bisphosphate. From these data the association constants for the binding of this organic phosphate to deoxyhemoglobin and oxyhemoglobin were calculated at different pH values. The maximum number of protons absorbed upon binding to oxyhemoglobin was determined as well. The maximum number of protons bound to deoxyhemoglobin upon binding of D-glycerate 2,3-bisphosphate was measured independently. From the pH dependence of the association constants and the maximum number of protons absorbed it could be concluded that only one D-glycerate 2,3-bisphosphate can be bound to both deoxyhemoglobin and oxyhemoglobin.

Binding Sites↗
PubMed1995

Pediococcus acidilactici ldhD gene: cloning, nucleotide sequence, and transcriptional analysis.

The gene encoding D-lactate dehydrogenase was isolated on a 2.9-kb insert from a library of Pediococcus acidilactici DNA by complementation for growth under anaerobiosis of an Escherichia coli lactate dehydrogenase and pyruvate-formate lyase double mutant. The nucleotide sequence of ldhD encodes a protein of 331 amino acids (predicted molecular mass of 37,210 Da) which shows similarity to the family of D-2-hydroxyacid dehydrogenases. The enzyme encoded by the cloned fragment is equally active on pyruvate and hydroxypyruvate, indicating that the enzyme has both D-lactate and D-glycerate dehydrogenase activities. Three other open reading frames were found in the 2.9-kb insert, one of which (rpsB) is highly similar to bacterial genes coding for ribosomal protein S2. Northern (RNA) blotting analyses indicated the presence of a 2-kb dicistronic transcript of ldhD (a metabolic gene) and rpsB (a putative ribosomal protein gene) together with a 1-kb monocistronic rpsB mRNA. These transcripts are abundant in the early phase of exponential growth but steadily fade away to disappear in the stationary phase. Primer extension analysis identified two distinct promoters driving either cotranscription of ldhD and rpsB or transcription of rpsB alone.

Amino Acid Sequence↗
PubMed1993

L-serine production by a methylotroph and its related enzymes.

The production process of L-serine from methanol and glycine has been developed using a methylotroph with the serine pathway. Consecutive reactions of two enzymes, methanol dehydrogenase (MDH) and serine hydroxymethyltransferase (SHMT) are involved in the production. We screened a high producer, Hyphomicrobium methylovorum, which is an obligate methylotroph. With resting cells of the bacterium, 24 mg/ml of L-serine was produced from 100 mg/ml of glycine and 48 mg/ml of methanol in 3 days under optimal conditions. Next, a glycine-resistant mutant GM2 showed improved serine production (32-34 mg/ml). The mutant GM2 was found to have elevated activities of MDH and SHMT. Since there has so far been little report on the systematic characterization of enzymes of the serine pathway in methylotrophs, not only the above two enzymes but also the other three enzymes in H. methylovorum were purified and characterized: MDH, SHMT and hydroxypyruvate reductase (HPR) were crystallized; serine-glyoxylate aminotransferase (SGAT) and glycerate kinase (GK) were purified to homogeneity. As a result, all these enzymes were found to be stable against preservation and to exist abundantly in the bacterium. The gene of SHMT was cloned and its deduced amino acid sequence had homology to those of Escherichia coli (55%) and rabbit liver (44%), whereas the enzyme of the bacterium was immunochemically distinguishable from those of microorganisms other than Hyphomicrobium strains and mammalian livers.

Alcohol Oxidoreductases↗
PubMed1992

Coupling of Carbon Dioxide Fixation to the Oxyhydrogen Reaction in the Isolated Chloroplast of Chlamydomonas reinhardtii.

The oxyhydrogen reaction (the reduction of O(2) to water by H(2)) in the presence of CO(2) was studied in the isolated Chlamydomonas reinhardtii chloroplast by monitoring the rate of (14)CO(2) incorporation into acid-stable products in the dark. The endogenous rate of CO(2) uptake (50-125 nmol/mg chlorophyll per h) was increased about 3- to 4-fold by ATP and additionally when combined with glucose, ribose-5-phosphate, and glycerate-3-phosphate. The rate was diminished 50 to 75%, respectively, when H(2) was replaced by N(2) or by air. Decrease in CO(2) uptake by dl-glyceraldehyde was taken to indicate that the regenerative phase and complete Calvin cycle turnover were involved. Diminution of CO(2) incorporation by rotenone, antimycin A, and 2,5-dibromo-3-methyl-6-isopropanol-p-benzoquinone was attributed to an inhibition of the oxyhydrogen reaction, resulting in an elevated NADPH/NADP ratio. If so, then the diminished CO(2) uptake could have been by "product inhibition" of the carbon metabolic network. Our data are consistent with the proposal (H. Gaffron [1942] J Gen Physiol 26: 241-267) that CO(2) fixation coupled to the oxyhydrogen reaction is dependent to some extent on exchloroplastic metabolism. This support is primarily ATP provided by mitochondrial respiration.

Journal Article↗
PubMed2000

Metabolic activity decreases as an adaptive response to low internal oxygen in growing potato tubers.

Plants lack specialised organs and circulatory systems, and oxygen can fall to low concentrations in metabolically active, dense or bulky tissues. In animals that tolerate hypoxia or anoxia, low oxygen triggers an adaptive inhibition of respiration and metabolic activity. Growing potato tubers were used to investigate whether an analogous response exists in plants. Oxygen concentrations fall below 5% in the centre of growing potato tubers. This is accompanied by a decrease of the adenylate energy status, and alterations of metabolites that are indicative of a decreased rate of glycolysis. The response to low oxygen was investigated in more detail by incubating tissue discs from growing tubers for 2 hours at a range of oxygen concentrations. When oxygen was decreased in the range between 21% and 4% there was a partial inhibition of sucrose breakdown, glycolysis and respiration. The energy status of the adenine, guanine and uridine nucleotides decreased, but pyrophosphate levels remained high. The inhibition of sucrose breakdown and glycolysis was accompanied by a small increase of sucrose, fructose, glycerate-3-phosphate, phosphenolpyruvate, and pyruvate, a decrease of the acetyl-coenzymeA:coenzymeA ratio, and a small increase of isocitrate and 2-oxoglutarate. These results indicate that carbon fluxes are inhibited at several sites, but the primary site of action of low oxygen is probably in mitochondrial electron transport. Decreasing the oxygen concentration from 21% to 4% also resulted in a partial inhibition of sucrose uptake, a strong inhibition of amino acid synthesis, a decrease of the levels of cofactors including the adenine, guanine and uridine nucleotides and coenzymeA, and attenuated the wounding-induced increase of respiration and invertase and phenylalanine lyase activity in tissue discs. Starch synthesis was maintained at high rates in low oxygen. Anoxia led to a diametrically opposed response, in which glycolysis rose 2-fold to support fermentation, starch synthesis was strongly inhibited, and the level of lactate and the lactate:pyruvate ratio and the triose-phosphate:glycerate-3-phosphate ratio increased dramatically. It is concluded that low oxygen triggers (i) a partial inhibition of respiration leading to a decrease of the cellular energy status and (ii) a parallel inhibition of a wide range of energy-consuming metabolic processes. These results have general implications for understanding the regulation of glycolysis, starch synthesis and other biosynthetic pathways in plants, and reveal a potential role for pyrophosphate in conserving energy and decreasing oxygen consumption.

Adenine Nucleotides↗