Combined action of an enzyme and a metal catalyst on the conversion of d-glucose/d-fructose mixtures into d-mannitol

A process involving both a bio- and a chemo-catalyst has been applied for the conversion of d-glucose/d-fructose mixtures into d-mannitol. Good yields (62–66%) were obtained by using d-glucose isomerase immobilised on silica in combination with a copper-on-silica catalyst (water, pH ∼7, 70°, 50 kg/cm² of hydrogen, trace amounts of buffer, Mg(II), borate, and EDTA). Non-enzymic isomerisation and degradation reactions are negligible under these reaction conditions.     

The influence of pH and weak-acid anions on the dehydration of d-fructose

The influence of the pH (1–6) on the rates and yields in the dehydration of d-fructose to 5-hydroxymethyl-2-furaldehyde (HMF) and the rehydration of HMF to levulinic and formic acids at 175° has been studied by using a stirred tank-reactor. The conversion rate of d-fructose passes through a minimum at pH 3.1, whereas at pH τ 3.9 no formation of HMF occurred and at pH τ 2.7 no formation of levulinic acid occurred. Isomerisation to d-glucose is observed at pH τ4.5. When a weak-acid anion, which functions as a base catalyst, is present at pH 3, the yield of HMF is lowered and isomerisation occurs.     

Effect of oxyanions on the glucose isomerase catalysed equilibrium: 1. Complexes of d-glucose and d-fructose with germanate

The complexing parameters of d-glucose and d-fructose with germanate, derived from various forms of germanium dioxide, have been studied under the conditions pertaining to the d-glucose isomerase (d-xylose isomerase, d-xylose ketol-isomerase, EC 5.3.1.5) reaction. The interaction of germanate with d-glucose and d-fructose at various pH values has been investigated by means of optical rotation methods. The effects of temperature and concentration on the extent of complex formation are reported. The results are used to predict suitable conditions for the enhancement of d-fructose yield in the reaction of d-glucose with this enzyme.     

Effect of oxyanions on the d-glucose isomerase catalysed equilibrium: 2. Effect of germanate on the equilibrium of d-glucose and d-fructose with immobilized d-glucose isomerase

The addition of germanate anions to high d-glucose feed syrups, which are passed through an immobilized d-glucose isomerase [xylose isomerase, d-xylose ketol-isomerase, EC 5.3.1.5] column, displaces a ca. 50/50 d-glucose/d-fructose mixture (produced in the absence of germanate) in favour of d-fructose. A maximum conversion of 94% from a d-glucose feed (40% w/v) is obtained with no detrimental effect on the enzyme. This is related to the germanate: sugar ratio. Optimization of the d-fructose yield from d-glucose germanate substrate has been carried out. The effects due to temperature, pH and concentration were taken into consideration. Confirmation of the quantitative identification of the d-fructose was obtained by isotope dilution analysis. The theory behind the displacement is also discussed, and shows close agreement with practical results.     

Metabolism of D-fructose by Arthrobacter pyridinolis

Previous studies showed that Arthrobacter pyridinolis can transport and utilize d-glucose only after prior growth on certain Krebs cycle intermediates. In contrast, we found that d-fructose was taken up and metabolized by A. pyridinolis without special prior conditions of growth. d-Fructose was first converted to d-fructose-1-phosphate by a phosphoenolpyruvate (PEP):D-fructose phosphotransferase. This activity required both supernatant and pellet fractions from d-fructose-grown cells centrifuged at 150,000 x g. The d-fructose-1-phosphate formed was converted to d-fructose-1, 6-diphosphate. Mutants deficient in PEP:d-fructose phosphotransferase and d-fructose-1-phosphate kinase, or d-fructose-1, 6-diphosphatase (FDPase) were unable to grow on d-fructose but retained the normal ability to use d-glucose. Mutants forming reduced amounts of FDPase were completely unable to grow on d-fructose but were still capable of limited growth on Krebs cycle intermediates. A requirement for higher levels of FDPase for growth on d-fructose than for growth on Krebs cycle intermediates was also indicated by the higher specific activities of FDPase in d-fructose-grown cells than in cells grown on l-malate or amino acids.     

Transport and catabolism of D-fructose by Spirillum itersomii

Spirillum itersonii ATCC 12639 utilized d-fructose but neither d-glucose nor d-gluconate as a sole source of carbon and energy. The substrate saturation kinetics for d-fructose and d-glucose uptake by whole cells indicated the presence of a carrier-mediated transport system for d-fructose but not for d-glucose. The d-fructose uptake activity was induced (10- to 12-fold increase) during growth on d-fructose-Casamino Acids (CA) or d-glucose-CA medium, but not CA alone. d-Fructose uptake activity was stimulated by Na(+) or Li(+), but was inhibited by KCN, NaN(3), 2,4-dinitrophenol, and p-chloromercuribenzoate. High specific activities of glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase were detected in extracts of cells cultured on d-fructose-CA medium. These enzymatic activities were undetectable in extracts of cells grown in CA or succinate-CA medium. No decrease in the maximally induced specific activities of these enzymes occurred after the addition of succinate to cells during exponential growth on d-fructose-CA. Fructose 1,6-diphosphate aldolase and glucose-6-phosphate isomerase specific activities were approximately the same irrespective of cultural conditions. These results indicated that d-glucose was not utilized by cells of S. itersonii because this bacterium was impermeable to this hexose.     

Separation of two receptor sites in a single labellar sugar receptor of the flesh-fly by treatment with p-chloromercuribenzoate

A 3 min treatment of a single sugar receptor with 0·5 mM p-chloromercuribenzoate (PCMB) did not affect its response to d-fructose, but depressed completely its response to d-glucose. This is the first direct evidence of the presence of two different sites in the sugar receptor of the fly.No specific protection by d-glucose on PCMB treatment suggested that PCMB did not react at a glucose-binding site but did react at a specific site indispensable to simulation by d-glucose.Various sugars were examined and classified into two groups according to the effects of PCMB treatment on the sugar receptor. They correspond to those effective in the furanose and pyranose forms, respectively. The pyranose group was further divided into two subclasses according to the presence or absence of three successive equatorial hydroxyl groups regardless of their positions. The results are discussed in relation to the structures that are common to furanose stimulating sugars.     

Hydrogenation of fructose on Ru/C catalysts

The hydrogenation of D-fructose on Ru/C catalysts was studied. Under the conditions applied (1 bar H2, 72 degrees C), the furanose forms of D-fructose react, while the pyranose forms do not. However, all anomers adsorb with comparable strength on the surface. The reaction rate is controlled by product inhibition. The selectivity to D-mannitol can be increased from 47 to 63% by promotion of Pd/C and Pt/C catalysts with Sn.     

The influence of the initial and catalyst concentrations on the dehydration of d-fructose

The dehydration at 95° of d-fructose (0.25m-1.0m) to 5-hydroxymethyl-2-furaldehyde (HMF) and the rehydration of HMF (0.25-1.0m) to levulinic and formic acids in 0.5-2m HCl has been studied. The conversion rate of d-fructose was proportional to the Hammett activity. The acidity had a smaller influence on the conversion rate of HMF, although it was not proportional to the catalyst concentration. The rehydration of HMF was faster in the presence of d-fructose. The yield of levulinic acid was independent of the catalyst concentration, but was lower at higher initial concentrations of d-fructose and HMF, and a kinetic model has been derived. The formation of humin was of an overall order 1.3 in an intermediate between d-fructose and HMF, and of an order 1.7 in an intermediate between HMF and levulinic acid.     

Efficient conversion of d-glucose into d-sorbitol over MCM-41 supported Ru catalyst prepared by a formaldehyde reduction process

Ru/MCM-41 catalyst prepared by an impregnation-formaldehyde reduction method showed higher catalytic activity and sorbitol selectivity than other catalysts in the hydrogenation of glucose. SEM and XRD indicated the partial surface properties of Ru/MCM-41. Moreover, Ru dispersion and Ru surface area of Ru/MCM-41 were determined by pulse chemisorption, and the result further proved that Ru/MCM-41 had higher catalytic activity. A catalyst recycling experiment demonstrated that Ru/MCM-41 was a better catalyst and it could be reused three or four times. A speculated mechanism was proposed to illustrate the detailed process of d-glucose hydrogenation to produce sorbitol.     

Efficient conversion of d-glucose into d-sorbitol over MCM-41 supported Ru catalyst prepared by a formaldehyde reduction process

Ru/MCM-41 catalyst prepared by an impregnation–formaldehyde reduction method showed higher catalytic activity and sorbitol selectivity than other catalysts in the hydrogenation of glucose. SEM and XRD indicated the partial surface properties of Ru/MCM-41. Moreover, Ru dispersion and Ru surface area of Ru/MCM-41 were determined by pulse chemisorption, and the result further proved that Ru/MCM-41 had higher catalytic activity. A catalyst recycling experiment demonstrated that Ru/MCM-41 was a better catalyst and it could be reused three or four times. A speculated mechanism was proposed to illustrate the detailed process of d-glucose hydrogenation to produce sorbitol.     

Metabolism of D-fructose in Aerobacter aerogenes: analysis of mutants lacking D-fructose 6-phosphate kinase and D-fructose 1,6-diphosphatase

The relative significance of the pathways for the conversion of d-fructose to d-fructose 1,6-diphosphate via d-fructose 1-phosphate or d-fructose 6-phosphate in Aerobacter aerogenes PRL-R3 was assessed by observing growth patterns of mutants lacking either d-fructose 6-phosphate kinase or d-fructose 1,6-diphosphatase. The mutant lacking d-fructose 6-phosphate kinase grew well on d-fructose or glycerol but not on d-glucose, whereas the mutant lacking d-fructose 1,6-diphosphatase grew on d-glucose but not on d-fructose or glycerol. The data indicate that the pathway of d-fructose metabolism is primarily through d-fructose 1-phosphate rather than d-fructose 6-phosphate.     

Metabolism of some polyols by Rhizobium meliloti

The utilization of d-mannitol, d-arabitol, and d-sorbitol by Rhizobium meliloti was studied in extracts from mannitol-grown cells. Two different polyol dehydrogenases were induced by any of these polyols: (i) a nicotinamide adenine dinucleotide (NAD)-arabitol dehydrogenase and (ii) a NAD-sorbitol dehydrogenase, whereas polyol phosphate dehydrogenases were absent. d-Arabitol dehydrogenase was observed to act on both d-arabitol and d-mannitol, but d-sorbitol dehydrogenase acted specifically on d-sorbitol. d-Arabitol was oxidized to d-xylulose, d-mannitol and d-sorbitol were oxidized to d-fructose. An adenosine triphosphate-linked hexokinase which acts on d-fructose and absence of hexose isomerase were also detected in this organism.     

The modulation of membrane fluidity by hydrogenation processes. II. Homogeneous catalysis and model biomembranes

A homogeneous catalyst, chlorotris (triphenylphosphine) rhodium (I) has been incorporated into model biomembrane structures in the form of lipid bilayer dispersions in water. This enables the hydrogenation of the double bonds of the unsaturated lipids within the bilayers to be accomplished. To decide the optimum conditions for efficient hydrogenation the reaction conditions have been varied. The effect of catalyst concentration, hydrogen gas pressure and lipid composition (with and without cholesterol) have all been studied. The partition of the catalyst into the lipid medium was checked by rhodium analysis. The results show that an increase of catalyst concentration or an increase of hydrogen gas pressure leads to increasing rates of hydrogenation. Successful hydrogenation was accomplished with different types of lipid dispersions (mitochondrial, microsomal and erythrocyte lipids). A selectivity of the homogeneous hydrogenation process is indicated. The polyunsaturated fatty acyl residues are hydrogenated at an earlier stage and at a faster rate than the monoenoic acids. Furthermore, an increase in the proportion of cholesterol to lipid within the bilayer structures causes a progressive decrease in the rate of hydrogenation. The fluidity of the lipid bilayers can be altered to such an extent by the hydrogenation process that new sharp endotherms corresponding to the order-disorder transition of saturated lipids occur at temperatures as high as 319 K. Some potential uses of hydrogenation for the modulation of cell membrane fluidity are discussed as well as the design of new types of catalyst molecules.     

Complexes of carbohydrates with aluminate ion. Aldose-ketose interconversion on anion-exchange resin (aluminate and hydroxide forms)

Kinetic parameters for aldose and ketose transformations in the d-glucose-d-mannose-d-fructose system at 27° on aluminate resin and hydroxide resin were obtained. On both resins, hydroxide ion functions as the catalyst for isomerization. By forming a complex with d-fructose, resin-bound aluminate ion stabilizes the ketose and permits high yields (up to 72%) of d-fructose from d-glucose. The effect of temperature on d-glucose-to-d-fructose conversion was studied; lower temperatures give the higher maximum yields. Maltose is converted into maltulose in moderately high yield (63%) at 24° on aluminate resin; higher yields are not possible at this temperature because of a marked tendency for maltulose to undergo elimination of d-glucose at C-4.     

Characterization of recombinant Aspergillus fumigatus mannitol-1-phosphate 5-dehydrogenase and its application for the stereoselective synthesis of protio and deuterio forms of D-mannitol 1-phosphate

A putative long-chain mannitol-1-phosphate 5-dehydrogenase from Aspergillus fumigatus (AfM1PDH) was overexpressed in Escherichia coli to a level of about 50% of total intracellular protein. The purified recombinant protein was a approximately 40-kDa monomer in solution and displayed the predicted enzymatic function, catalyzing NAD(H)-dependent interconversion of d-mannitol 1-phosphate and d-fructose 6-phosphate with a specific reductase activity of 170 U/mg at pH 7.1 and 25 degrees C. NADP(H) showed a marginal activity. Hydrogen transfer from formate to d-fructose 6-phosphate, mediated by NAD(H) and catalyzed by a coupled enzyme system of purified Candida boidinii formate dehydrogenase and AfM1PDH, was used for the preparative synthesis of d-mannitol 1-phosphate or, by applying an analogous procedure using deuterio formate, the 5-[2H] derivative thereof. Following the precipitation of d-mannitol 1-phosphate as barium salt, pure product (>95% by HPLC and NMR) was obtained in isolated yields of about 90%, based on 200 mM of d-fructose 6-phosphate employed in the reaction. In situ proton NMR studies of enzymatic oxidation of d-5-[2H]-mannitol 1-phosphate demonstrated that AfM1PDH was stereospecific for transferring the deuterium to NAD+, producing (4S)-[2H]-NADH. Comparison of maximum initial rates for NAD+-dependent oxidation of protio and deuterio forms of D-mannitol 1-phosphate at pH 7.1 and 25 degrees C revealed a primary kinetic isotope effect of 2.9+/-0.2, suggesting that the hydride transfer was strongly rate-determining for the overall enzymatic reaction under these conditions.     

Selective hydrogenolysis of raw glycerol to 1,2-propanediol over Cu–ZnO catalysts in fixed-bed reactor

The catalytic properties of Cu–ZnO catalysts for glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) were tested in a fixed-bed reactor at 250 °C and 2.0 MPa H₂. The relation between composition, surface properties, and catalytic performance of glycerol hydrogenation of Cu–ZnO catalysts was studied using nitrogen adsorption (BET methods), XRD, H₂ temperature-programmed reduction, and N₂O chemisorptions. It was found that there was a close link between the surface CuO amount of Cu–ZnO catalyst and the reactivity for glycerol hydrogenation. The Cu–ZnO catalyst (Cu/Zn = 1.86) which had the highest surface Cu amount showed the best catalytic activity for glycerol hydrogenolysis. Furthermore, Cu–ZnO catalyst presented good stability and remarkable catalytic activity for glycerol hydrogenolysis to 1,2-PDO using raw glycerol derived from the fat saponification as feedstock.     

Anomeric specificity of human liver and B-cell glucokinase: modulation by the glucokinase regulatory protein

The anomeric specificity of the wild-type recombinant forms of human liver and B-cell glucokinase was investigated using radioactive anomers of d-glucose as tracers. With d-glucose at anomeric equilibrium and at 30 degrees C, the maximal velocity, Hill number, and K(s) amounted, respectively, to 16 micromol min(-1) mg(-1), 1.8 and 6.9 mM in the case of liver glucokinase, and 7.3 micromol min(-1) mg(-1), 2.0 and 7.1 mM in the case of B-cell glucokinase. Whether at 20-22 or 30 degrees C, the maximal velocity, Hill number, and K(m) were significantly lower with alpha-d-glucose than with beta-d-glucose in both liver and B-cell glucokinase. As a result of these differences, the reaction velocity was higher with alpha-d-glucose at low hexose concentrations, while the opposite situation prevailed at high hexose concentrations. In the presence of 0.2 mM d-fructose 6-phosphate, the glucokinase regulatory protein caused a concentration-related inhibition of d-glucose phosphorylation, such an effect fading out at high concentrations of either d-glucose or glucokinase relative to that of its regulatory protein. The phosphorylation of alpha-d-glucose by liver glucokinase appeared more resistant than that of beta-d-glucose to the inhibitory action of d-fructose 6-phosphate, as mediated by the glucokinase regulatory protein. Such a phenomenon failed to achieve statistical significance in the case of the B-cell glucokinase. It is proposed that this information, especially the novel findings concerning the anomeric difference in both Hill number and sensitivity to the glucokinase regulatory protein, should be taken into account when considering the respective contributions of alpha- and beta-d-glucose to the overall phosphorylation of equilibrated d-glucose by glucokinase.     

Oxidation of d-fructose with vanadium(V): A kinetic approach

The kinetics of the oxidation of d-fructose with vanadium(V) in perchloric acid have been studied. The reaction is of first order with respect to the [Fructose], but the values of the rate constant increase slightly with increasing [V(V)]. In the range from 0.002–0.02m V(V), the inverse of the second-order rate constant is linearly related to the inverse of [V(V)]. Sodium hydrogensulfate and perchlorate accelerate the reaction, the effect of the former salt being greater. At a constant [H⁺] and ionic strength, the reaction is of first order with respect to [HSO₄⁻]. At constant ionic strength, the reaction is of third order with respect to [H⁺]. The activation parameters have been determined. The data obtained have been compared with those for simpler mono- and poly-hydric alcohols. A possible three-step mechanism involving CH bond fission and yielding glucosones as primary products has been suggested.