Biomedical subjects

F Malaisse-Lagae

Publications and source records attributed to F Malaisse-Lagae.

At least 19 recordsLinked to original sources

PubMed1995

D-glucose metabolism in cross-linked pancreatic islets.

D-glucose metabolism was investigated in pancreatic islets that underwent cross-linking of intracellular proteins by dimethyl suberimidate. Both the utilization of D-[5-3H]glucose and oxidation of D-[U-14C]glucose were much more severely affected at high (16.7 mM) than at low (2.8 mM) concentration of the hexose, when comparing cross-linked to control islets. The preferential stimulation of D-[U-14C]glucose oxidation relative to D-[5-3H]glucose utilization, resulting from an increase in hexose concentration, was not abolished, however, in cross-linked islets. Likewise, the activation of phosphofructokinase in glucose-stimulated islets did not appear to be impaired in cross-linked islets, the islet content in tritiated acidic metabolites generated from D-[5-3H]glucose failing to be increased in cross-linked islets. It is proposed, therefore, that the impaired responsiveness of cross-linked islets to a rise in D-glucose concentration might be attributable to an altered regulation of glucokinase, as possibly resulting from a missing interaction of the enzyme with GLUT-2.

Animals↗

PubMed1995

Insulinotropic action of (2S)-2-benzyl-3-(cis-hexahydro-2-isoindolinylcarbonyl) propionate. II. Ionophoretic and conformational aspects.

1. The non-sulphonylurea insulinotropic agent sodium (2S)-2-benzyl-3-(cis-hexahydro-2-isoindolinylcarbonyl) propionate (KAD-1229) was found to display calcium ionophoretic activity in an artificial membrane model. 2. Conformation analysis indicated that a complex between calcium and KAD-1229, with a 1:2 stoichiometry, indeed displays favourable attributes for ionophoretic activity across a hydrophobic environment. 3. It is speculated that the ionophoretic property of KAD-1229 might participate to the remodelling of cationic fluxes evoked by this insulinotropic agent in pancreatic islet cells.

Animals↗

PubMed1995

NADP-malate dehydrogenase activity in rat erythrocytes. Comparison with pyruvate kinase in relation to coupling with lactate dehydrogenase.

The present study explores the possible channelling of pyruvate generated by either pyruvate kinase or NADP-malate dehydrogenase to lactate dehydrogenase in cross-linked and permeabilized erythrocytes. The generation of both unlabelled and 14C-labelled pyruvate and lactate was measured in rat erythrocytes, which were prepared for cross-linking with dimethyl suberimidate and permeabilization by digitonin and then exposed to unlabelled or 14C-labelled malate and/or phospho-enol-pyruvate. Rat erythrocytes were found to display NADP-malate dehydrogenase activity. Under conditions in which the generation rates of pyruvate from either phospho-enol-pyruvate (15 microM) or malate (0.5 mM) were not vastly different from one another, a greater fraction of the 2-keto acid was converted to lactate when produced from phospho-enol-[1-14C]pyruvate rather than [U-14C]malate. This difference was most obvious when the availability of exogenous NADH was close to or somewhat below that theoretically required to ensure full conversion of endogenously formed pyruvate to lactate. These findings are compatible with the view that pyruvate generated at the pyruvate kinase level is converted to lactate more efficiently than pyruvate produced in the reaction catalysed by NADP-malate dehydrogenase.

Animals↗

PubMed1994

Impaired FAD-glycerophosphate dehydrogenase activity in islet and liver homogenates of fa/fa rats.

The mitochondrial FAD-linked enzyme glycerophosphate dehydrogenase plays a key role in the pancreatic B-cell glucose sensing device. In the present study, the activity of this enzyme was examined in islets of fa/fa rats in which inherited diabetes mellitus is associated with obesity, hyperinsulinism and severe insulin resistance. The specific activity of both FAD-linked glycerophosphate dehydrogenase and glutamate dehydrogenase were decreased in islet and liver homogenates prepared from fa/fa, as compared to Fa/Fa, rats, this coinciding with a low ratio between glutamateoxalacetate and glutamate-pyruvate transaminase activity in both islet and liver extracts, islet hyperplasia, hyperinsulinemia and hepatic steatosis in the hyperglycemic fa/fa rats. It is speculated that a low activity of FAD-linked glycerophosphate dehydrogenase in the pancreatic B-cell may participate to the perturbation of glucose homeostasis in fa/fa rats, like in other animal models of non-insulin-dependent diabetes mellitus.

Alanine Transaminase↗

PubMed1994

Ionophoretic activity of meglitinide analogues.

The sodium and calcium ionophoretic activity of meglitinide and three of its hypoglycemic analogs, namely S3075, KAD-1229 and repaglinide was examined in an artificial membrane model. All agents were able to cause the translocation of 45Ca and 22Na from an aqueous solution into an immiscible organic phase. The results were compatible with the formation of a calcium-ionophore complex with a 1-2 stoichiometry. The ionophoretic activity ranged in the following hierarchy: KAD-1229 > S3075 > repaglinide = meglitinide and, hence, did not closely parallel the insulinotropic potential of these non-sulfonylurea hypoglycemic agents. It is proposed, therefore, that the ionophoretic capacity of meglitinide analogs may not represent an essential determinant of their insulin-releasing action.

Benzamides↗

PubMed1994

Insulinotropic action of meglitinide analogs: concentration-response relationship and nutrient dependency.

The insulinotropic action of meglitinide was compared to that of its analogs S 3075, A-4166, KAD-1229 and repaglinide. None of these hypoglycemic agents significantly enhanced insulin output from rat pancreatic islets incubated for 90 min in the absence of exogenous nutrient. However, all these agents, when tested at a 10 microM concentration, augmented insulin release evoked by either 7 mM D-glucose or 10 microM succinic acid monomethyl ester (SAM). In this respect, meglitinide was a less efficient secretagogue than the other non-sulfonylurea hypoglycemic agents. Moreover, in the presence of 7 mM D-glucose, the lowest concentration of the drug required to cause a significant increase in insulin output decreased from about 1.0 microM for meglitinide to 0.1 microM with A-4166, KAD-1229 or repaglinide and even close to 10 nM in the case of S 3075. The concentration-response relationship thus yielded the following hierarchy, S 3075 > KAD-1229 = repaglinide > A-4166 > meglitinide, there being a difference of more than two orders of magnitude between the weakest and most potent agent.

Animals↗

PubMed1992

Dual anomeric specificity of phosphomannoisomerase assessed by 2D phase sensitive 13C EXSY NMR.

The reversible conversion between D-mannose 6-phosphate and D-fructose 6-phosphate catalyzed by yeast phosphomannoisomerase was studied by phase sensitive 2D 13C-(1H) EXSY NMR spectroscopy at 100.623 MHz, using 13C enriched substrates in the C2 position of the D-hexose 6-phosphates. The unique pair of isomerization cross-peaks observed in the 2D EXSY map correlates the 13C2 resonances of the beta-anomers of both D-[2-13C]-mannose 6-phosphate and D-[213C]-fructose 6-phosphate. This indicates that phosphomannoisomerase specifically catalyzes the reversible conversion between beta-D-mannose 6-phosphate and beta-D-fructose 6-phosphate. Since phosphoglucoisomerase was recently found to catalyze specifically the interconversion of alpha-D-glucose 6-phosphate and beta-D-fructose 6-phosphate, the beta-anomer of the ketohexose ester could be directly channeled in a multi-enzyme system involving phosphoglucoisomerase, phosphomannoisomerase and phosphofructokinase.

Fructosephosphates↗

PubMed1992

Dual anomeric specificity and dual anomerase activity of phosphoglucoisomerase quantified by two-dimensional phase-sensitive 13C EXSY NMR.

The reversible conversion between D-glucose 6-phosphate and D-fructose 6-phosphate catalyzed by yeast phosphoglucoisomerase was studied by phase sensitive two-dimensional 13C-[1H] EXSY NMR spectroscopy at 150.869 and 125.759 MHz, using 13C-enriched substrates in the C2 position of the D-hexose 6-phosphates. The shape of the build-up curves of the cross-peaks associated with the 13C2 resonances of the alpha- and beta-anomers of both D-[2-13C]glucose 6-phosphate and D-[2-13C]fructose 6-phosphate reveals that phosphoglucoisomerase selectively catalyzes the reversible conversion between alpha-D-[2-13C]glucose 6-phosphate and beta-D-[2-13C]fructose 6-phosphate. Quantitative analysis of the build-up curves by three different methods allowed us to conclude that phosphoglucoisomerase not only selectively channels the latter isomerization but also considerably accelerates the anomerization of both D-hexose 6-phosphates. The rate constants of anomerization were indeed much higher in the presence than in the absence of enzyme. The major finding in the present study consists in the anomeric specificity of phosphoglucoisomerase toward the beta-anomer of D-fructose 6-phosphate both as a substrate and a product, contrary to previous proposals. This finding supports recent evidence suggesting the direct channelling of beta-D-fructose 6-phosphate from phosphoglucoisomerase to phosphofructokinase.

Catalysis↗

PubMed1992

Preservation of the anomeric specificity of glucose-induced insulin release in partially pancreatectomized rats.

Attenuation, suppression or even inversion of the normal preference of glucose-stimulated insulin release for the alpha-anomer of the hexose was recently proposed to represent a feature of Beta-cell glucotoxicity in Type 2 (non-insulin-dependent) diabetes mellitus. Since recent reports emphasize the possible significance of Beta-cell secretory hyperactivity as a determinant of such a glucotoxicity, the anomeric specificity of glucose-induced insulin release was examined in normoglycaemic partially pancreatectomized rats. About 80-85% of the pancreas was removed, the animals then being given sucrose via their drinking water up to the time of killing. In these animals, alpha-D-glucose was more efficient than beta-D-glucose in stimulating insulin release from the perfused pancreas, the alpha/beta ratio in insulin output not being significantly different from that found in control rats. It is concluded, therefore, that the anomeric malaise, taken as a manifestation of Beta-cell glucotoxicity, it attributable to hyperglycaemia rather than to Beta-cell secretory hyperactivity.

Animals↗

PubMed1991

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates. Study by 13C NMR of proton and deuteron exchange.

The exchange of protons and deuterons by phosphoglucoisomerase during the single passage conversion of D-[2-13C,1-2H]fructose 6-phosphate in H2O or D-[2-13C]fructose 6-phosphate in D2O to D-[2-13C]glucose 6-phosphate, as coupled with the further generation of 6-phospho-D-[2-13C]gluconate in the presence of excess glucose-6-phosphate dehydrogenase was investigated by 13C NMR spectroscopy of the latter metabolite. In H2O, the intramolecular deuteron transfer from the C1 of D-fructose 6-phosphate to the C2 of D-glucose 6-phosphate amounted to 65%, a value only slightly lower than the 72% intramolecular proton transfer in D2O. Both percentages, especially the latter one, were lower than those previously recorded during the single passage conversion of D-[1-13C,2-2H]glucose 6-phosphate in H2O or D-[1-13C]glucose 6-phosphate in D2O to D-fructose 6-phosphate and then to D-fructose 1,6-bisphosphate. These differences indicate that the sequence of interactions between the hexose esters and the binding sites of phosphoglucoisomerase is not strictly in mirror image during, respectively, the conversion of the aldose phosphate to ketose phosphate and the opposite process.

Binding Sites↗

PubMed1991

Metabolism of tritiated D-glucose in rat erythrocytes.

The metabolism of D-[U-14C]glucose, D-[1-14C]glucose, D-[6-14C]glucose, D-[1-3H]glucose, D-[2-3H]glucose, D-[3-3H]glucose, D-[3,4-3H]glucose, D-[5-3H]glucose, and D-[6-3H]glucose was examined in rat erythrocytes. There was a fair agreement between the rate of 3HOH production from either D-[3-3H]glucose and D-[5-3H]glucose, the decrease in the 2,3-diphosphoglycerate pool, its fractional turnover rate, the production of 14C-labeled lactate from D-[U-14C]glucose, and the total lactate output. The generation of both 3HOH and tritiated acidic metabolites from D-[3,4-3H]glucose indicated incomplete detritiation of the C4 during interconversion of fructose-1,6-bisphosphate and triose phosphates. Erythrocytes unexpectedly generated 3HOH from D-[6-3H]glucose, a phenomenon possibly attributable to the detritiation of [3-3H]pyruvate in the reaction catalyzed by glutamate pyruvate transaminase. The production of 3HOH from D-[2-3H]glucose was lower than that from D-[5-3H]glucose, suggesting enzyme-to-enzyme tunneling of glycolytic intermediates in the hexokinase/phosphoglucoisomerase/phosphofructokinase sequence. The production of 3HOH from D-[1-3H]glucose largely exceeded that of 14CO2 from D-[1-14C]glucose, a situation tentatively ascribed to the generation of 3HOH in the phosphomannoisomerase reaction. It is further speculated that the adjustment in specific radioactivity of D-[1-3H]glucose-6-phosphate cannot simultaneously match the vastly different degrees of isotopic discrimination in velocity at the levels of the reactions catalyzed by either glucose-6-phosphate dehydrogenase or phosphoglucoisomerase. The interpretation of the present findings thus raises a number of questions, which are proposed as a scope for further investigations.

Acids↗

PubMed1991

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: distinction of the 1-monodeutero-isotopomers of D-fructose 6-phosphate by 1H NMR spectroscopy.

The 1H NMR spectrum obtained with the alpha- and beta-anomers of D-[1-2H]fructose 6-phosphate generated from D-glucose 6-phosphate sequentially exposed in D2O to phosphoglucoisomerase, phosphofructokinase and fructose-1,6-diphosphatase differed from that recorded when the deuterated ketohexose phosphate was produced from D-mannose 6-phosphate sequentially exposed in D2O to phosphomannoisomerase, phosphofructokinase and fructose-1,6-diphosphatase. The identification of the 2 isotopomers of D-fructose 6-phosphate by 1H NMR spectroscopy provides a new tool to assess the relative extent of interconversion of hexose phosphates in the reactions catalyzed by phosphoglucoisomerase and phosphomannoisomerase, respectively.

Deuterium↗

PubMed1991

Generation of 3HOH from D-[6-3H]glucose by erythrocytes: role of pyruvate alanine interconversion.

Human and rat erythrocytes were found to generate 3HOH from D-[6(N)-3H]glucose. The rate of 3HOH production represented 7-10% of the glycolytic flux. The generation of 3HOH appeared attributable, in part at least, to the detritiation of [3-3H]pyruvate during the interconversion of the 2-keto acid and L-alanine in the reaction catalyzed by glutamate-pyruvate transaminase. Indeed, purified pig heart glutamate-pyruvate transaminase, as well as homogenates prepared from rat erythrocytes or pancreatic islets, catalyzed the generation of 3HOH from L-[3-3H]alanine. When the production of tritiated pyruvate from L-[3-3H]alanine was coupled to the conversion of the 2-keto acid to L-lactate, the production of 3HOH accounted for one-third of the reaction velocity, the latter failing to display isotopic discrimination. In these experiments, the production of 3HOH was abolished by amino-oxyacetate. Likewise, in intact rat erythrocytes, aminooxyacetate inhibited the generation of 3HOH and tritiated L-alanine from D-[6-3H]glucose (or D-[1-3H]glucose), as well as the generation of 3HOH from L-[3-3H]alanine. In pancreatic islets, however, aminooxyacetate failed to affect significantly the generation of 3HOH from D-[6-3H]glucose. These findings indicate that the generation of 3HOH from D-[6-3H]glucose is mainly attributable to an intermolecular tritium transfer in transaminase reaction, at least in cells devoid of mitochondria.

Alanine↗

PubMed1991

Variable expression of isotopic discrimination in metabolic flows.

Isotopic discrimination in reaction velocity may affect to a variable extent the estimation of metabolic flow when a metabolic intermediate is catabolized by two pathways with different degrees of discrimination. This was explored in erythrocytes exposed to 14C- or 3H-labelled D-glucose in the absence or presence of menadione. In the absence of menadione, when the pentose phosphate pathway accounted for only 5% of the D-glucose 6-phosphate turnover, the oxidation of C1-protonated or C1-deuterated D-[U-14C]glucose and D-[1-14C]glucose, mixed with the homologous non-radioactive D-[1-1H]glucose or D-[1-2H]glucose, indicated that, relative to the phosphorylation of the hexose, C1-deuterated D-glucose was less efficiently converted to 14CO2 than C1-protonated D-glucose. Moreover, in the absence of menadione, non-deuterated D-[U-14C]glucose and D-[1-14C]glucose were more efficiently oxidized in cells exposed to D-[1-2H]glucose rather than D-[1-1H]glucose. In the presence of menadione, which increased more than ten-fold the flow rate through the pentose phosphate pathway, the phenomenon of isotopic discrimination was either revealed or masked. These data indicate that the phenomenon of isotopic discrimination may indeed affect to a variable extent the estimation of a given metabolic flow.

Animals↗

PubMed1990

Regulation of glucokinase by a fructose-1-phosphate-sensitive protein in pancreatic islets.

In the post-microsomal supernatant of pancreatic islets, prepared from fasted or fed rats, D-fructose 1-phosphate increased the activity of glucokinase by 20-30% as measured in the presence of D-glucose 6-phosphate and D-fructose 6-phosphate. Such an activation was less marked than that found in liver extracts. The islet cytosol was also found to inhibit purified liver glucokinase, and this effect was antagonized by D-fructose 1-phosphate. In the presence of hexose 6-phosphates, partially purified islet glucokinase was inhibited by the hepatic glucokinase regulatory protein in a D-fructose-1-phosphate-sensitive manner. In intact islets, D-glyceraldehyde stimulated the generation of 14C-labelled D-fructose 1-phosphate from D-[U-14C]glucose and increased the production of 3H2O from D-[5-3H]glucose. These findings suggest that the activity of glucokinase in islet cells may be regulated by a protein mediating the antagonistic effects of D-fructose 6-phosphate and D-fructose 1-phosphate in a manner qualitatively similar to that operating in hepatocytes, but with lower efficiency.

Animals↗

PubMed1990

The interaction of phosphorylase a with D-glucose displays alpha-stereospecificity.

Half-maximal inhibition of phosphorylase a required a much lower concentration of alpha-D-glucose (4 mM) than of the beta-anomer (14 mM) and of 1-deoxyglucose (about 25 mM). beta-D-Glucose was almost ineffective at concentrations of 1-2.5 mM, but at 50 mM the two anomers were equipotent. A similar picture emerged when the stimulatory effects of the glucose anomers and of 1-deoxyglucose were investigated on the inactivation of phosphorylase by phosphorylase phosphatase. However, upon addition of either glucose anomer (5-20 mM) to a suspension of isolated hepatocytes, the inactivation of phosphorylase occurred at the same rate. It is shown that, in the latter conditions, the rate of intracellular mutarotation considerably exceeds the rate of glucose transport. This results presumably in a rapid anomeric equilibrium in the liver cells.

Animals↗

PubMed1990

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: isotopic discrimination between hydrogen and deuterium.

The discrimination between the isotopes of hydrogen in the reaction catalyzed by yeast phosphoglucoisomerase is examined by NMR, as well as by spectrofluorometric or radioisotopic methods. The monodirectional conversion of D-glucose 6-phosphate to D-fructose 6-phosphate displays a lower maximal velocity with D-[2-2H]glucose 6-phosphate than unlabelled D-glucose 6-phosphate, with little difference in the affinity of the enzyme for these two substrates. About 72% of the deuterium located on the C2 of D-[1-13C,2-2H]glucose 6-phosphate is transferred intramolecularly to the C1 of D-[1-13C,1-2H]fructose 6-phosphate. The velocity of the monodirectional conversion of D-[U-14C]glucose 6-phosphate (or D-[2-3H]glucose 6-phosphate) to D-fructose 6-phosphate is virtually identical in H2O and D2O, respectively, but is four times lower with the tritiated than 14C-labelled ester. In the monodirectional reaction, the intramolecular transfer from the C2 of D-[2-3H]glucose 6-phosphate is higher in the presence of D2O than H2O. Whereas prolonged exposure of D-[1-13C]glucose 6-phosphate to D2O, in the presence of phosphoglucoisomerase, leads to the formation of both D-[1-13C,2-2H]glucose 6-phosphate and D-[1-13C,1-2H]fructose 6-phosphate, no sizeable incorporation of dueterium from D2O on the C1 of D-[1-13C]fructose 1,6-bisphosphate is observed when the monodirectional conversion of D-[1-13C]glucose 6-phosphate occurs in the concomitant presence of phosphoglucoisomerase and phosphofructokinase. The latter finding contrasts with the incorporation of hydrogen from 1H2O or tritium from 3H2O in the monodirectional conversion of D-[2-3H]glucose 6-phosphate and unlabelled D-glucose 6-phosphate, respectively, to their corresponding ketohexose esters.

Carbon Isotopes↗

PubMed1990

Phosphoglucoisomerase-catalysed interconversion of hexose phosphates. Kinetic study by 13C n.m.r. of the phosphoglucoisomerase reaction in 2H2O.

The fate of D-[2-13C]glucose 6-phosphate exposed to phosphoglucoisomerase (glucose-6-phosphate isomerase, EC 5.3.1.9) in 2H2O was monitored by 13C-n.m.r. spectroscopy. The generation of the anomers of both D-[2-13C]fructose 6-phosphate and D-[2-13C,2-2H]glucose 6-phosphate followed a single-exponential pattern. The rate constant, which was proportional to the enzyme concentration, was about 14 times higher, however, in the former than in the latter case. The disappearance of D-[2-13C,2-1H]glucose 6-phosphate occurred in a bi-exponential manner, the rate constants for the fast and the slow processes being in fair agreement with those obtained for the generation of D-[2-13C]fructose 6-phosphate and D-[2-13C,2-2H]glucose 6-phosphate respectively. These findings indicate that the process of equilibration of D-[2-13C]glucose 6-phosphate and D-[2-13C]fructose 6-phosphate is at least one order of magnitude faster than the intermolecular proton transfer involving the deuterons from the solvent. Such a difference provides strong support to the view that the inverconversion of hexose phosphates in the reaction catalysed by phosphoglucoisomerase proceeds in two distinct steps, the second of which occurs according to two competing modalities with either an intramolecular or an intermolecular proton transfer.

Carbon Isotopes↗