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PubMed1988

Inactivation of type MM phosphoglycerate mutase by sulfhydryl group reagents during facial embryogenesis.

Type MM phosphoglycerate mutase from free dissected mandibular processes from embryonic rats was reversibly inactivated by tetrathionate, p-chloromercuribenzoate, and Hg2+. Titration with p-chloromercuribenzoate showed the existence of two sulfhydryl groups per enzyme subunit, the modification of which produced a progressive decline in enzyme activity. The apparent Km values for substrate and cofactor were not affected by tetrathionate treatment. Phosphoglycerate mutase inactivated by tetrathionate and by p-chloromercuribenzoate was unable to form the functionally active phosphorylenzyme when mixed with glycerate-2,3-P2. Glycerate-2,3-P2 protected against tetrathionate but failed to protect against Hg2+ and p-chloromercuribenzoate.

Animals↗
PubMed1992

Involvement of arginine residues in the allosteric activation and inhibition of Synechocystis PCC 6803 ADPglucose pyrophosphorylase.

ADPglucose pyrophosphorylase (EC 2.7.7.27) from the cyanobacterium Synechocystis PCC 6803 was desensitized to the effects of allosteric ligands by treatment with the arginine reagent, phenylglyoxal. Enzyme modification by phenylglyoxal resulted in inactivation when the enzyme was assayed under 3P-glycerate-activated conditions. There was little loss of the catalytic activity assayed in the absence of activator. Pi, 3P-glycerate, and pyridoxal-P were able to protect the enzyme from inactivation, whereas substrates gave minimal protection. The protective effect exhibited by Pi and 3P-glycerate was dependent on effector concentration. MgCl2 enhanced the protection afforded by 3P-glycerate. The enzyme partially modified by phenylglyoxal was more resistant to 3P-glycerate activation and Pi inhibition than the unmodified form. Vmax at saturating 3P-glycerate concentrations and the apparent affinity of the enzyme toward Pi were decreased upon phenylglyoxal modification. Incorporation of labeled phenylglyoxal into the enzyme was proportional to the loss of activity. Pi and 3P-glycerate nearly completely prevented incorporation of the reagent to the protein. Results suggest that one arginine residue per mol of enzyme subunit is involved in the binding of allosteric effector in the cyanobacterial ADPglucose pyrophosphorylase.

Amino Acid Sequence↗
PubMed1989

Gene for the ribulose-1,5-bisphosphate carboxylase small subunit protein of the marine chromophyte Olisthodiscus luteus is similar to that of a chemoautotrophic bacterium.

The photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39] small subunit protein is encoded by the gene rbcS in the chloroplast genome of the unicellular alga Olisthodiscus luteus. This observation contrasts sharply with that seen in terrestrial plants and green algae, where rbcS is nuclear-localized. In this study, the O. luteus rbcS gene has been sequenced. The predicted primary structure of the protein sequence is 139 amino acids in length and lacks an N-terminal signal sequence. Unexpectedly, the O. luteus rbcS amino acid sequence shows the greatest similarity (56% identity) to that of the chemolithotrophic bacterium Alcaligenes eutrophus. A comparison of the N-terminal amino acid rbcS sequence of A. eutrophus to those of O. luteus and brown alga Fucus species shows extensive sequence similarity (68.3% identity). This observation suggests that the rbcS genes of these organisms are evolutionary homologues and may provide useful information in the study of small-subunit function.

Alcaligenes↗
PubMed1990

31P NMR studies of spinach leaves and their chloroplasts.

An experimental arrangement is described which enables high quality 31P NMR spectra of compressed spinach leaf pieces to be continuously recorded in which all the resonances observed (cytoplasmic and vacuolar Pi, glycerate-3-P, nucleotides) were sharp and well resolved. 31P NMR spectra obtained from intact chloroplasts showed a distinct peak of stromal Pi. An upfield shift of the stromal Pi resonance was associated with a decrease in the external Pi and vice versa. Nucleotides were largely invisible to NMR in intact chloroplasts, whereas the same nucleotides reappeared in a typical 31P NMR spectrum of an acid extract of intact chloroplasts. Perfusion of compressed spinach leaf pieces with a medium containing Pi triggered a dramatic increase in the vacuolar Pi over 12 h. Addition of choline to the Pi-free perfusate of compressed leaf pieces resulted in a steady accumulation of phosphorylcholine in the cytoplasmic compartment at the expense of cytoplasmic Pi. When a threshold of cytoplasmic Pi concentration was attained, Pi was drawn from the vacuole to sustain choline phosphorylation. In spinach leaves, the vacuole represents a potentially large Pi reservoir, and cycling of Pi through vacuolar influx (energy dependent) and efflux pathways is an efficient system that may provide for control over the cytosolic-free Pi and phosphorylated intermediate concentrations. 31P NMR spectra of neutralized perchloric acid extracts of spinach leaves showed well defined multipeak resonances (quadruplet) of intracellular phytate. The question of cytosolic Pi concentration in green cells is discussed.

Adenine Nucleotides↗
PubMed1976

Kinetic competence of a phosphoryl enzyme intermediate in the glucose-1,6-p2 synthase-catalyzed reaction. Purification, properties, and kinetic studies.

Glucose-1,6-P2 synthase of beef brain which catalyzes the formation of glucose-1,6-P2 and glycerate-3-P from glycerate-1,3-P2 and glucose-1-P has been purified 700-fold with an overall recovery of 19%. The purification procedure involves an ammonium sulfate fractionation of the crude extract, DE52 and hydroxylapatite column chromatography and isoelectric focusing. The isolated enzyme appears to be homogeneous by sodium dodecyl sulfate gel electrophoresis. Its molecular weight is estimated to be about 70,000 by gel filtration on Sephadex G-200 which agrees with the value obtained by sodium dodecyl sulfate gel electrophoresis. A phosphoryl enzyme intermediate in the catalytic reaction is indicated by the following evidence: glycerate-1,3-P2[1-32P] labels the enzyme. The label is removed by acceptor substrates such as glucose-1-P. Using a rapid quenching device at 23 degrees and pH 8.0, the first order rate constant for phosphorylation of the enzyme is 20 s-1, compared with an overall rate with the best acceptor, glucose-1-P, of 19 s-1. Dephosphorylation by glucose-1-P is at 37 s-1. Mg2+ is required for both phosphoryl transfers and the overall reaction. In the complete reaction the fraction of enzyme that is phosphorylated depends on the concentrations of glycerate-1,3-P2 and the concentration and nature of the acceptor in a way that could be predicted from the steady state parameters, the Km values, and the kinetic constants observed for the single turnover. Reciprocal plots of initial rates as a function of both substrate concentrations are families of parallel lines. The 32P-labeled phosphoryl enzyme intermediate was found to be acid-stable and somewhat alkaline-labile. Phosphoserine was identified from the partial acid hydrolysate of a protease digest of [32P] phosphoryl enzyme by two-dimensional thin layer chromatography.

Animals↗
PubMed1982

Phylogeny and ontogeny of the phosphoglycerate mutases - III. Inactivation of rabbit muscle phosphoglycerate mutase (type M isozyme) by the sulfhydryl group reagents.

1. The three phosphoglycerate mutase isozymes from mammals (types M, B and MB isozymes) differ in their sensitivity to the - SH group reagents. 2. Rabbit muscle phosphoglycerate mutase (type M isozyme) is reversibly inactivated by tetrathionate, rho-chloromercuribenzoate and Hg2+. 3. Titration with rho-chloromercuribenzoate shows the existence of two sulfhydryl groups per enzyme subunit, the modification of which produces a progressive decline in enzyme activity. 4. The apparent Km values for substrate and cofactor are not affected by tetrathionate treatment. 5. Phosphoglycerate mutase inactivated by tetrathionate and by rho-chloromercuribenzoate is unable to form the functionally active phosphorylenzyme when mixed with glycerate-2,3-P2, and is not protected by the cofactor against heating. 6. Glycerate-2,3-P2 protects against tetrathionate treatment, but fails to protect against Hg2+ and rho-chloromercuribenzoate inactivation.

Animals↗
PubMed1988

5'-Nucleotidase activities in human erythrocytes. Identification of a purine 5'-nucleotidase stimulated by ATP and glycerate 2,3-bisphosphate.

A purine 5'-nucleotidase has been separated by DEAE-Trisacryl chromatography from other 5'-nucleotidase activities present in human haemolysates and purified approx. 30,000-fold by subsequent chromatography on Blue Sepharose. The enzyme has an Mr of around 250,000, displays hyperbolic substrate-saturation kinetics and hydrolyses preferentially IMP, GMP and their deoxy counterparts. It is much less active with AMP and dAMP. The purine 5'-nucleotidase is inhibited by Pi, and is strongly stimulated by ATP, dATP and GTP, and by glycerate 2,3-bisphosphate. Stimulators decrease Km and increase Vmax. Glycerate 2,3-bisphosphate is the most potent stimulator of the enzyme and, under physiological conditions, over-rides the influence of the other effectors. Glycerate 2,3-bisphosphate also influences the binding of the enzyme to DEAE-Trisacryl, as evidenced by the different elution profile obtained with fresh as compared with outdated blood. It is concluded that the glycerate 2,3-bisphosphate-stimulated purine 5'-nucleotidase is responsible for the dephosphorylation of IMP and GMP, but not of AMP, in human erythrocytes.

2,3-Diphosphoglycerate↗
PubMed1976

Rates of phosphorylation and dephosphorylation of phosphoglycerate mutase and bisphosphoglycerate synthase.

Phosphoglycerate mutase and bisphosphoglycerate synthase (mutase) can both be phosphorylated by either glycerate-1,3-P2 or glycerate-2,3-P2 to form phosphohistidine enzymes. The present study uses a rapid quench procedure to determine if, for each enzyme, the formation of the phosphorylated enzyme and phosphate transfer from the enzyme can occur at rates consistent with the overall reactions. With bisphosphoglycerate synthase from horse red blood cells (glycerate-1,3-P2 leads to glycerate-2,3-P2) at pH 7.5, 25 degrees, phosphorylation of the enzyme appears rate-limiting, k = 13.5 s-1, compared with kcat = 12.5 s-1 for the overall synthase rate. Phosphoryl transfer from the enzyme to phosphoglycerate occurs at 38 s-1 at 4 degrees and was too fast to measure at 25 degrees. With chicken muscle phosphoglycerate mutase the half-times were too short to measure under optimal conditions. The rate of enzyme phosphorylation by glycerate-2,3-P2 at pH 5.5, 4 degrees, could account for the overall reaction rate of 170 s-1. The rate of phosphoryl transfer from the enzyme to glycerate-3-P was too rapid to measure under the same conditions. It is concluded that the phosphorylated enzymes have kinetic properties consistent with their participation as intermediates in the reactions catalyzed by these enzymes.

Animals↗
PubMed1983

Determination of C distribution in photosynthetic serine and phosphoglycerate from grape leaves.

Serine and phosphoglyceric acid are the classical marker intermediates of photorespiration and reductive carbon assimilation in C(3) plants. The present paper introduces a new and fast method for the determination of (14)C distribution in these compounds by selective elimination of C-3 (NaIO(4)) or C-1 (ninhydrin/ceric sulfate). Reproducibility of the procedure was found to be better than +/-1% upon degradation of [U-(14)C]serine and [U-(14)C]glycerate standards.Determination of labeling patterns in (dephosphorylated) phosphoglycerate and serine, extracted from grape leaf discs (Vitis vinifera L.) after administration of (14)CO(2) for 1 minute showed that (14)C distribution in serine changes considerably with changing assimilatory conditions. Interpretations of data basing on unusual labeling patterns of serine must therefore be accepted with caution.

Journal Article↗
PubMed1977

Stereochemistry of the dTDP-glucose oxidoreductase reaction.

The stereochemical course of the dTDP-glucose oxidoreductase (EC 4.2.1.46) reaction was studied using enzyme partially purified from Escherichia coli and dTDP-(6R)- and (6S)-[4-2H, 6-3H]glucose as substrate. The latter was prepared enzymatically by reduction of (3R)- and (3S)-3-P-[3-3H]glycerate to the 1-deuterated 3-P-glyceraldehyde with (4S)-[4-2H]NADH, followed first by conversion to glucose-1-P with the glycolytic enzymes, and then by transformation into the dTDP derivative. The stereospecifically labeled dTDP-glucose samples were mixed with nonlabeled carrier material and converted to dTDP-4-keto-6-deoxyglucose, which contained a chiral methyl group as shown by chirality analysis of the acetic acid resulting from Kuhn-Roth oxidation of the sugar nucleotide. These results confirm that the hydrogen transfer from C4 to C6 is intramolecular and show that the migrating hydrogen replaces the 6-hydroxyl group with inversion of configuration. Assuming that the hydrogen transfer, since it is intramolecular, must be suprafacial, it follows that the elimination of water from C5 and C6 is formally syn, whereas the reduction of the resulting delta5,6-double bond formally involves an anti addition of H+ and H-.

Deuterium↗
PubMed1983

Isolation of a cDNA clone for human X-linked 3-phosphoglycerate kinase by use of a mixture of synthetic oligodeoxyribonucleotides as a detection probe.

We have obtained a cDNA clone encoding most of human X-linked 3-phosphoglycerate kinase (PGK; ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3). Total mRNA was prepared from human adenocarcinoma-derived cell line LS174T and used for cDNA preparation. Double-stranded cDNA was inserted, after tailing with oligo(dC), into the plasmid vector pBR327 and cloned in Escherichia coli K-12. Transformants were screened by colony hybridization with a mixture of 32P-labeled oligodeoxyribonucleotides. A pool of hexadecamers complementary to all 32 possible sequences encoding amino acids 291-296 of X-linked PGK was used for the initial screen. One clone among 2,500 gave a strong positive signal. Plasmid DNA from this clone was purified and characterized by hybridization first to the hexadecamer probe mixture and then to an undecamer probe consisting of a mixture of four sequences. The cloned fragment hybridizes preferentially to DNA from human cells with five X chromosomes. DNA sequence analysis has established that the 1.2-kilobase-pair fragment encodes PGK from amino acid 121 through the COOH terminus.

Amino Acid Sequence↗
PubMed1997

Critical role of human bisphosphoglycerate mutase Cys22 in the phosphatase activator-binding site.

The enzymatic activities catalyzed by bisphosphoglycerate mutase (BPGM, EC 5.4.2.4) have been shown to occur at a unique active site, with distinct binding sites for diphosphoglycerates and monophosphoglycerates. The physiological phosphatase activator (2-phosphoglycolate) binds to BPGM at an undetermined site. BPGM variants were constructed by site-directed mutagenesis of three amino acid residues in the active site to identify residues specifically involved in the binding of the monophosphoglycerates and 2-phosphoglycolate. Substitution of Cys22 by functionally conservative residues, Thr or Ser, caused a great decrease in 2-phosphoglycolate-stimulated phosphatase activity and in the Ka value of the activator, whereas it caused no change in other catalytic activities or in the Km values of 2,3-diphosphoglycerate (2,3-DPG) and glycerate 3-phosphate (3-PG, EC 1.1.1.12), indicating that Cys22 is specifically involved either directly or indirectly in 2-phosphoglycolate binding. Kinetic experiments showed that the Ka of the cofactor and the Km of 3-PG were affected by the substitution of Ser23 indicating that this residue is necessary for the fixation of both 3-PG and 2-phosphoglycolate. The R89K variant has previously been shown to have a modified Km value for monophosphoglycerates, however, its affinity for 2-phosphoglycolate is unaltered, suggesting that Arg89 is specifically involved in monophosphoglycerates binding. CD spectroscopic studies of substrates and cofactor binding showed that 2,3-DPG induced structural modifications of normal and mutated enzymes which could be due to protein phosphorylation. Addition of 2-phosphoglycolate to phosphorylated proteins with normal affinity for the cofactor produced spectra with the same characteristics as unphosphorylated species. In summary, monophosphoglycerates and 2-phosphoglycolate have partially distinct binding sites in human BPGM. The specific implication of the Cys22 residue in 2-phosphoglycolate binding is of great significance in the design of analogs of therapeutic benefit.

Binding Sites↗
PubMed1989

Does glyceraldehyde enter pancreatic islet metabolism via both the triokinase and the glyceraldehyde phosphate dehydrogenase reactions? A study of these enzymes in islets.

Glyceraldehyde has been known to be an insulin secretagogue for more than 15 years. It has been (reasonably) assumed that glyceraldehyde enters the glycolytic pathway via its phosphorylation by ATP to form glyceraldehyde phosphate, a reaction catalyzed by the enzyme triokinase, and that subsequent metabolism is identical to that of glucose. glucose. However, up to now there have been no studies verifying the presence of triokinase in the pancreatic beta cell. We report here that (1) the activity of triokinase in pancreatic islets is very low, indicating that the activity is intrinsically low and/or the enzyme was rapidly inactivated during the preparation of tissue for assay; (2) the activity is much lower than glucose phosphorylating activity (hexokinase plus glucokinase) in islets, even though glyceraldehyde is a more efficient insulin secretagogue than glucose; (3) glyceraldehyde phosphate dehydrogenase from pancreatic islets can use glyceraldehyde as a substrate in place of glyceraldehyde phosphate (the Vmax of glyceraldehyde phosphate dehydrogenase from islets when glyceraldehyde is the substrate is 20-fold that of triokinase when glyceraldehyde is the substrate); and (4) the Km of glyceraldehyde phosphate dehydrogenase with respect to glyceraldehyde (4.8 mM) is similar to the concentration of glyceraldehyde that gives one-half maximal rates of insulin release from pancreatic islets, whereas the Km of triokinase with respect to glyceraldehyde is much lower (less than 50 microM). These data suggest that besides stimulating insulin release in islets via its entering metabolism by phosphorylation to glyceraldehyde phosphate in the triokinase reaction, glyceraldehyde could be phosphorylated by Pi in the glyceraldehyde phosphate dehydrogenase reaction to form glycerate 1-phosphate which is probably unmetabolizable in islets. The second reaction could drastically increase the NADH/NAD ratio in islets without providing substrates for hydrogen shuttles that reoxidize cytosolic NADH. Since an increased NAD(P)H/NAD(P) ratio is believed to be a key part of the signal for insulin release, such a mechanism would explain the potent insulinotropism of glyceraldehyde in short-term experiments. In addition, the formation of unmetabolizable acids may explain the toxic effects of long-term exposure of islets to glyceraldehyde and why glyceraldehyde causes the beta cell to become acidic, whereas glucose does not.

Animals↗
PubMed2005

D-GLYCERATE 3-KINASE, the last unknown enzyme in the photorespiratory cycle in Arabidopsis, belongs to a novel kinase family.

D-GLYCERATE 3-KINASE (GLYK; EC 2.7.1.31) catalyzes the concluding reaction of the photorespiratory C2 cycle, an indispensable ancillary metabolic pathway to the photosynthetic C3 cycle that enables land plants to grow in an oxygen-containing atmosphere. Except for GLYK, all other enzymes that contribute to the C2 cycle are known by their primary structures, and the encoding genes have been identified. We have purified and partially sequenced this yet missing enzyme from Arabidopsis thaliana and identified it as a putative kinase-annotated single-copy gene At1g80380. The exclusive catalytic properties of the gene product were confirmed after heterologous expression in Escherichia coli. Arabidopsis T-DNA insertional knockout mutants show no GLYK activity and are not viable in normal air; however, they grow under elevated CO2, providing direct evidence of the obligatory nature of the ultimate step of the C2 cycle. The newly identified GLYK is both structurally and phylogenetically distinct from known glycerate kinases from bacteria and animals. Orthologous enzymes are present in other plants, fungi, and some cyanobacteria. The metabolic context of GLYK activity in fungi and cyanobacteria remains to be investigated.

Amino Acid Sequence↗
PubMed1982

Isozymes of the glycolytic enzymes in endosperm from developing castor oil seeds.

Ion filtration chromatography on diethylaminoethyl-Sephadex A-25 has been used to separate two isozymes each of triose phosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, glycerate 3-phosphate kinase, enolase, and phosphoglycerate mutase from homogenates of developing castor oil (Ricinus communis L. cv. Baker 296) seeds. Crude plastid fractions, prepared by differential centrifugation, were enriched in one of the isozymes, whereas the cytosolic fractions were enriched in the other. These data (and data published previously) indicate that plastids from developing castor oil seeds have a complete glycolytic pathway and are capable of conversion of hexose phosphate to pyruvate for fatty acid synthesis. The enzymes of this pathway in the plastids are isozymes of the corresponding enzymes located in the cytosol.

Journal Article↗
PubMed2006

Anaerobic central metabolic pathways in Shewanella oneidensis MR-1 reinterpreted in the light of isotopic metabolite labeling.

It has been proposed that during growth under anaerobic or oxygen-limited conditions, Shewanella oneidensis MR-1 uses the serine-isocitrate lyase pathway common to many methylotrophic anaerobes, in which formaldehyde produced from pyruvate is condensed with glycine to form serine. The serine is then transformed through hydroxypyruvate and glycerate to enter central metabolism at phosphoglycerate. To examine its use of the serine-isocitrate lyase pathway under anaerobic conditions, we grew S. oneidensis MR-1 on [1-13C]lactate as the sole carbon source, with either trimethylamine N-oxide (TMAO) or fumarate as an electron acceptor. Analysis of cellular metabolites indicated that a large percentage (>70%) of lactate was partially oxidized to either acetate or pyruvate. The 13C isotope distributions in amino acids and other key metabolites indicate that under anaerobic conditions, although glyoxylate synthesized from the isocitrate lyase reaction can be converted to glycine, a complete serine-isocitrate pathway is not present and serine/glycine is, in fact, oxidized via a highly reversible degradation pathway. The labeling data also suggest significant activity in the anapleurotic (malic enzyme and phosphoenolpyruvate carboxylase) reactions. Although the tricarboxylic acid (TCA) cycle is often observed to be incomplete in many other anaerobes (absence of 2-oxoglutarate dehydrogenase activity), isotopic labeling supports the existence of a complete TCA cycle in S. oneidensis MR-1 under certain anaerobic conditions, e.g., TMAO-reducing conditions.

Acetates↗
PubMed1993

The effects of hypothermia on the intracellular pH of erythrocytes studied using 31P NMR and endogenous compounds.

The effects of hypothermia on the intracellular pH of human erythrocytes were studied non-invasively using 31P NMR spectroscopy and the endogenous phosphorus-containing compounds glycerate 2,3-bisphosphate and inorganic phosphate. Specifically, the pH dependence of the 31P NMR chemical shifts of these compounds was used to measure the intracellular pH at 25 and 37 degrees C. The possibility of a non-pH-dependent change on the chemical shifts of the 2-P and 3-P resonances of glycerate 2,3-bisphosphate due to the presence of paramagnetic deoxy-haemoglobin (i.e., a pseudo-contact interaction) was investigated and found to have negligible effect under the present experimental conditions. The most probable reasons for this are that the deoxy-haemoglobin concentration was too small and/or the glycerate 2,3-bisphosphate does not get sufficiently close to the paramagnetic centre to be affected. The change in intracellular pH with temperature was consistent with that predicted by the alphastat hypothesis.

2,3-Diphosphoglycerate↗
PubMed1982

The effect of pH and D-glycerate 2,3-bisphosphate on the O2 equilibrium of normal and SH(beta 93)-modified human hemoglobin.

The present paper reports data for the effect of pH and D-glycerate 2,3-bisphosphate (D-glycerate-2,3-P2) on the oxygen equilibrium of normal and SH(beta 93)-modified human hemoglobin. At sufficiently high D-glycerate-2,3-P2 concentrations, both oxy and deoxy forms of HbA are saturated with the organic phosphate at all pH values between 6 and 9. Furthermore the difference in the affinity for D-glycerate-2,3-P2 between deoxy and oxy hemoglobin remains constant with pH, implying that the pK values of the Bohr effect groups in deoxy and oxyhemoglobin are not affected by the presence of D-glycerate-2,3-P2 on the hemoglobin molecule. In the hemoglobins modified in position beta 93, the difference in affinity between deoxy and oxy hemoglobin for D-glycerate-2,3-P2 decreases with decrease in pH due mainly to a decrease in the affinity of the deoxy form for D-glycerate-2,3-P2. The effect of the chemical modification appears to be primarily a change in pK of a Bohr group in deoxy hemoglobin which is especially pronounced in the presence of phosphates.

2,3-Diphosphoglycerate↗