Oxidation Of D-sorbitol Research Articles

Efficient production of the rare sugar l-gulose using a wheat-bran culture extract of Penicillium sp. KU-1.

We found that l-gulose, a rare sugar, was produced from d-sorbitol efficiently, using a wheat-bran culture extract of the fungus Penicillium sp. KU-1 isolated from soil. The culture extract showed enzyme activity for the oxidation of d-sorbitol to produce l-gulose; a high production yield of approximately 94% was achieved.

Substrate Inhibition: Oxidation of D-Sorbitol and D-Dulcitol by Mn(VII) in Alkaline Medium

Substrate Inhibition: Oxidation of D-Sorbitol and D-Dulcitol by Mn(VII) in Alkaline Medium

Overcoming NADPH product inhibition improves D-sorbitol conversion to L-sorbose

Gluconobacter oxydans sorbitol dehydrogenase (GoSLDH) exhibits a higher catalytic efficiency than other l-sorbose producing enzymes. During the reaction catalysed by GoSLDH, NADP+ is reduced to NADPH and d-sorbitol is oxidized to l-sorbose. However, GoSLDH activity is inhibited by the NADPH (Ki = 100 μM) formed during the enzymatic reaction. Therefore, Escherichia coligosldh-lrenox producing both GoSLDH for d-sorbitol oxidation and LreNOX (NAD(P)H oxidase from Lactobacillus reuteri) for NADP+ regeneration was generated and used for l-sorbose production. Whole cell biocatalysts with the LreNOX cofactor recycling system showed a high conversion rate (92%) of d-sorbitol to l-sorbose in the presence of low concentration of NADP+ (0.5 mM). By alleviating NADPH accumulation during the catalytic reactions, E. coligosldh-lrenox exhibited 23-fold higher conversion rate of d-sorbitol than E. coligosldh. l-Sorbose production by E. coligosldh-lrenox reached 4.1 g/L after 40 min, which was 20.5-fold higher than that of E. coligosldh. We also constructed G. oxydansgosldh and G. oxydansgosldh-lrenox strains, and they exhibited 1.2- and 2.9-fold higher conversion rates than the wild-type G. oxydans KCTC 1091. The results indicate that overcoming NADPH product inhibition using LreNOX improves chemical production in NADP+-dependent enzymatic reactions.

Aldopentoses as new substrates for the membrane-bound, pyrroloquinoline quinone-dependent glycerol (polyol) dehydrogenase of Gluconobacter sp.

Membrane-bound, pyrroloquinoline quinone (PQQ)-dependent glycerol dehydrogenase (GLDH, or polyol dehydrogenase) of Gluconobacter sp. oxidizes various secondary alcohols to produce the corresponding ketones, such as oxidation of D-sorbitol to L-sorbose in vitamin C production. Substrate specificity of GLDH is considered limited to secondary alcohols in the D-erythro configuration at the next to the last carbon. Here, we suggest that L-ribose, D- and L-lyxoses, and L-tagatose are also substrates of GLDH, but these sugars do not meet the substrate specificity rule of GLDH. The oxygen consumption activity of wild-type Gluconobacter frateurii cell membranes depends on several kinds of sugars as compared with that of the membranes of a GLDH-negative variant. Biotransformation of those sugars with the membranes was examined to determine the reaction products. A time course measuring the pH in the reaction mixture and the increase or decrease in substrates and products on TLC suggested that oxidation products of L-lyxose and L-tagatose were ketones with unknown structures, but those of L-ribose and D-lyxose were acids. The oxidation product of L-ribose was purified and revealed to be L-ribonate by HRMS and NMR analysis. Biotransformation of L-ribose with the membranes and also with the whole cells produced L-ribonate in nearly stoichiometric amounts, indicating that the specific oxidation site in L-ribose is recognized by GLDH. Since purified GLDH produced L-ribonate without any intermediate-like compounds, we propose here a reaction model where the first carbon in the pyranose form of L-ribose is oxidized by GLDH to L-ribonolactone, which is further hydrolyzed spontaneously to produce L-ribonate.

Substrate inhibition: Oxidation of D-sorbitol and D-mannitol by potassium periodate in alkaline medium

In the oxidation of D-sorbitol and D-mannitol by potassium periodate in alkaline media, substrate inhibition was observed with both substrates, i.e., a decrease in the rate of the reaction was observed with an increase in the concentration of substrate. The substrate inhibition was attributed to the formation of stable complex between the substrate and periodate. The reactions were found to be first order in case of periodate and a positive fractional order with hydroxide ions. Arrhenius parameters were calculated for the oxidation of sorbitol and mannitol by potassium periodate in alkali media.

Best combination of promoter and micellar catalyst for the rapid conversion of sorbitol to glucose

Kinetic data for oxidation of D-sorbitol to glucose by hexavalent chromium in aqueous medium and aqueous surfactant medium (SDS, TX-100) have been reported. Effect of promoter such as PA, bipy and phenanthroline on the reaction has been investigated. The reaction is performed under pseudo first order condition with an excess of substrate over the oxidant. The reaction is first order with respect to substrate and oxidant. The micelles have a catalytic effect on the reaction. Combination of phen and TX-100 produces almost twelve times increase in rate of oxidation.

Electrophoretically deposited carbon nanotubes as a novel support for electrogenerated silica–dehydrogenase bioelectrodes

The electrophoretic deposition of carbon nanotubes (CNT) on glassy carbon electrode was used here for the development of porous matrix with enhanced electroactive surface area. The prepared layer displayed a catalytic activity toward NADH oxidation and was used as a support for the d-sorbitol dehydrogenase immobilization. The electrochemically assisted deposition (EAD) method was performed to generate around carbon nanotubes sol–gel biocomposite films containing the enzyme and a cationic polyelectrolyte. The response of the immobilized enzyme strongly depended on the parameters of sol–gel deposition as well as the thickness of carbon nanotubes layer. The electrocatalytic oxidation of d-sorbitol using such modified electrode was used here as a model to discuss the interest of such silica–carbon nanotubes composite in the field of bioelectrochemistry and biosensors.

Sorbitol dehydrogenase of Aspergillus niger, SdhA, is part of the oxido-reductive d-galactose pathway and essential for d-sorbitol catabolism

In filamentous fungi d-galactose can be catabolised through the oxido-reductive and/or the Leloir pathway. In the oxido-reductive pathway d-galactose is converted to d-fructose in a series of steps where the last step is the oxidation of d-sorbitol by an NAD-dependent dehydrogenase. We identified a sorbitol dehydrogenase gene, sdhA (JGI53356), in Aspergillus niger encoding a medium chain dehydrogenase which is involved in d-galactose and d-sorbitol catabolism. The gene is upregulated in the presence of d-galactose, galactitol and d-sorbitol. An sdhA deletion strain showed reduced growth on galactitol and growth on d-sorbitol was completely abolished. The purified enzyme converted d-sorbitol to d-fructose with Km of 50±5mM and vmax of 80±10U/mg.

Multiscale-Tailored Bioelectrode Surfaces for Optimized Catalytic Conversion Efficiency

We describe the elaboration of a multiscale-tailored bioelectrocatalytic system. The combination of two enzymes, D-sorbitol dehydrogenase and diaphorase, is studied with respect to the oxidation of D-sorbitol as a model system. The biomolecules are immobilized in an electrodeposited paint (EDP) layer. Reproducible and efficient catalysis of D-sorbitol oxidation is recorded when this system is immobilized on a gold electrode modified by a self-assembled monolayer of 4-carboxy-(2,5,7-trinitro-9-fluorenylidene)malonitrile used as a mediator. The insertion of mediator-modified gold nanoparticles into the EDP film increases significantly the active surface area for the catalytic reaction, which can be further enhanced when the whole system is immobilized in macroporous gold electrodes. This multiscale architecture finally leads to a catalytic device with optimized efficiency for potential use in biosensors, bioelectrosynthesis, and biofuel cells.

Electrochemically assisted deposition of sol–gel bio-composite with co-immobilized dehydrogenase and diaphorase

We report here that the electrochemically assisted deposition (EAD) of silica thin films can be a good strategy to co-encapsulate d-sorbitol dehydrogenase (DSDH) and diaphorase in an active form. This is achieved via the electrolysis of a hydrolyzed sol containing the biomolecules to initiate the poly-condensation of silica precursors upon electrochemically induced pH increase at the electrode/solution interface. DSDH was found to be very sensitive to the silica gel environment and the addition of a positively-charged polyelectrolyte was necessary to ensure effective operational behavior of the biomolecules. The composition of the sol and the conditions for electrolysis have been optimized with respect to the intensity of the electrochemical response to d-sorbitol oxidation. The K m of DSDH in the electrodeposited film was in the range of 3 mM, slightly better than the value determined biochemically in solution (6.5 mM). The co-immobilization of DSDH and diaphorase in this way led on the one hand to the possible reduction of NAD + to NADH (simultaneously to d-sorbitol oxidation) and on the other hand to the safe re-oxidation of the co-factor using a mediator (ferrocenedimethanol) as electron relay. The bioelectrocatalytic response looks promising for electro-enzymatic applications. To support this idea, the EAD of sol–gel bio-composite has been extended to macroporous electrodes displaying a much bigger electroactive surface area.

Engineering and modeling of thin, adhesive, microbial biocatalytic coatings for high intensity oxidations in multi-phase microchannel bioreactors

A model-based investigation of the reactivity of a multi-phase microchannel bioreactor for the oxidation of d-sorbitol to l-sorbose by viable Gluconobacter oxydans entrapped in an adhesive, bilayer, and nano-porous latex coating has been performed. Using kinetics and mass-transfer information from literature, the overall productivity of a single microchannel was determined. For liquid and gas superficial velocities typical for monoliths and channel diameters smaller than 1000 μm, volumetric l-sorbose formation rates larger than 30 g l −1 h −1 were predicted. Since the system was approximately kinetically controlled any effort to increase the coating reactivity, for example by using thinner topcoats or improving cell viability should result in a further increase of the overall reactivity. These modeling studies should provide the basis for engineering of channel geometry, biocatalytic coating nano-porosity and thickness, coating stability, optimal reactivity and multi-phase channel flow properties for future microchannel bioreactors for high intensity microbial oxidations.

Oxidation of D-Sorbitol to L-Sorbose with Immobilized Cells of Gluconobacter suboxydans

Oxidation of D-Sorbitol to L-Sorbose with Immobilized Cells of Gluconobacter suboxydans

Voltammetric determination of sorbite at a mechanically renewed copper electrode

Potentials and currents of D-sorbitol oxidation peaks as a function of polarization conditions for a copper electrode in situ renewed by mechanically cutting a 0.5-µm surface layer are studied by direct-current cyclic voltammetry. Oxidation peaks of sorbite emerge in cyclic voltammograms recorded in alkaline supporting electrolytes (0.05–0.10 M KOH and NaOH solutions) upon scanning the potential to the anodic region (E p = 0.50–0.58 V) and in the reverse direction (E p = 0.60–0.62 V). The shape and parameters of these peaks depend on the concentration of KOH, because of the different copper oxides involved in the oxidation of sorbite formed at the electrode surface. The regeneration of the electrode surface is the necessary condition for good reproducibility of the peak parameters. The signals obtained on the surface of the unrenewed electrodes are almost halved and less reproducible. The calibration graph of the current of the sorbite oxidation peak as a function of its concentration is linear in the range from 5 × 10−4 to 1 × 10−2 M.

Micellar Catalysis on Pentavalent Vanadium Ion Oxidation of D-Sorbitol in Aqueous Acid Media: A Kinetic Study

Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the con- centrations of D-sorbitol, vanadium(V), H + and HSO − . These observations remain unal- tered in the presence of externally added surfactants. The effects of the cationic surfactant (i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to dif- ferent extents. SDS and TX-100 can be used as catalysts in the production of D-glucose from D-sorbitol.

A pyrroloquinoline quinine-dependent membrane-bound d-sorbitol dehydrogenase from Gluconobacter oxydans exhibits an ordered Bi Bi reaction mechanism

A membrane-bound pyrroloquinoline quinine (PQQ)-dependent d-sorbitol dehydrogenase (mSLDH) in Gluconobacter oxydans participates in the oxidation of d-sorbitol to l-sorbose by transferring electrons to ubiquinone which links to the respiratory chain. To elucidate the kinetic mechanism, the enzyme purified was subjected to two-substrate steady-state kinetic analysis, product and substrate inhibition studies. These kinetic data indicate that the catalytic reaction follows an ordered Bi Bi mechanism, where the substrates bind to the enzyme in a defined order (first ubiquinone followed by d-sorbitol), while products are released in sequence (first l-sorbose followed by ubiquinol). From these findings, we proposed that the native mSLDH bears two different substrate-binding sites, one for ubiquinone and the other for d-sorbitol, in addition to PQQ-binding and Mg 2+-binding sites in the catalytic center.

A model system for increasing the intensity of whole-cell biocatalysis: Investigation of the rate of oxidation ofD-sorbitol toL-sorbose by thin bi-layer latex coatings of non-growingGluconobacter oxydans

We developed a novel <50-microm thick nano-porous bi-layer latex coating for preserving Gluconobacter oxydans, a strict aerobe, as a whole cell biocatalyst. G. oxydans was entrapped in an acrylate/vinyl acetate co-polymer matrix (T (g) approximately 10 degrees C) and cast into 12.7-mm diameter patch coatings (cellcoat) containing approximately 10(9) CFU covered by a nano-porous topcoat. The oxidation of D-sorbitol to L-sorbose was used to investigate the coating catalytic properties. Intrinsic kinetics was studied in microbioreactors using a pH 6.0 D-sorbitol, phosphate, pyruvate (SPP) non-growth medium at 30 degrees C, and the Michaelis-Menten constants determined. By using a diffusion cell, cellcoat and topcoat diffusivities, optimized by arresting polymer particle coalescence by glycerol and/or sucrose addition, were determined. Cryo-FESEM images revealed a two-layer structure with G. oxydans surrounded by <40-nm pores. Viable cell density, cell leakage, and oxidation kinetics in SPP medium for >150 h were investigated. Even though the coatings were optimized for permeability, approximately 50% of G. oxydans viability was lost during cellcoat drying and further reduction was observed as the topcoat was added. High reaction rates per unit volume of coating (80-100 g/L x h) were observed which agreed with predictions of a diffusion-reaction model using parameters estimated by independent experiments. Cellcoat effectiveness factors of 0.22-0.49 were observed which are 20-fold greater than any previously reported for this G. oxydans oxidation. These nano-structured coatings and the possibility of improving their ability to preserve G. oxydans viability may be useful for engineering highly reactive adhesive coatings for multi-phase micro-channel and membrane bioreactors to dramatically increase the intensity of whole-cell oxidations.

Gold based bimetallic catalysts for liquid phase applications

The liquid phase oxidation of D-Sorbitol has been carried out in water using oxygen as the oxidant in the presence of gold based catalyst. Au/C, Pt/C and Pd/C monometallic systems were compared to bimetallic Au/Pd and Au/Pt on carbon. A strong synergistic effect was observed producing a significant increase of reaction rate. Moreover, the addition of gold to Pd or Pt catalyst produced a system more resistant to oxygen poisoning allowing it to work also under a moderate pressure. The effect of varying the molar ratio of the metals has also been studied.

Synergetic effect of platinum or palladium on gold catalyst in the selective oxidation of D-sorbitol

Monometallic Au, Pt and Pd on carbon catalysts show poor activity in the liquid phase oxidation of D-sorbitol to gluconic/gulonic acids. However, by using bimetallic based catalysts (Au–Pt or Au–Pd) a great enhancement in the activity has been observed with respect to all the monometallic catalysts tested probably due to a synergetic effect between Au and Pt or Pd. In fact physical mixture of monometallic catalysts presented poor activity. Bimetallic showed a resistance to poisoning by dioxygen and by reaction products as high as gold monometallic catalyst, but also an improved selectivity toward monooxidation with respect to monometallic.

Characterization of recombinant xylitol dehydrogenase from Galactocandida mastotermitis expressed in Escherichia coli

The plasmid-encoded gene of xylitol dehydrogenase from the yeast Galactocandida mastotermitis was expressed in Escherichia coli at 25 °C. Recombinant enzyme was isolated in 70% yield using two steps of biomimetic affinity chromatography with the dye ligand Procion Red HE3B immobilized onto Sepharose 4B-CL. Similar to natural enzyme, recombinant xylitol dehydrogenase is a functional homotetramer with a stoichiometric content of catalytic zinc in each 37-kDa subunit. Though lacking bound Mg 2+ found in xylitol dehydrogenase isolated from yeast cell extracts, the recombinant enzyme is as active and stable as the native enzyme. Stereospecificity of enzymic hydrogen transfer from NADH has been determined by 1H-NMR and is 4-pro- R. A detailed steady-state kinetic analysis has been carried out for the enzymic reaction, polyol+NAD +↔ketose+NADH+H +, at pH 7.5 and 25 °C using xylitol and d-xylulose, the physiological polyol–ketose pair, as well as d-sorbitol and d-fructose. Primary deuterium kinetic isotope effects on steady-state kinetic parameters for oxidation of d-sorbitol and reduction of d-fructose have been measured at pH 7.5. Combined results of initial-rate analysis and isotope effect studies suggest that the enzyme utilizes a preferentially ordered kinetic mechanism in which NAD + binds before d-sorbitol and d-fructose is released before NADH. Dissociation of NADH appears to be the main rate-limiting step for d-sorbitol oxidation under substrate-saturated reaction conditions.

Electrochemical Oxidation of D-Sorbitol and D-Manitol on Platinum Monocrystalline Surfaces

The electrochemical oxidation of D-sorbitol and D-mannitol was studied on two sets of stepped platinum single-crystal surfaces vicinal to the basal plane (111), as well as on a set of surfaces with monoatomic steps vicinal to the surface Pt(100). The aim of this study, conducted by cyclic voltammetry, was to check the influence of the crystalline surface structure (regarding terrace and step orientations) on the electrochemical oxidation process of the two polyols in platinum. The electrochemical oxidation reactions of D-sorbitol and D-mannitol were shown to be markedly influenced by the symmetry of the bidimensional domains as well as by the distribution of the orientated defects (monoatomic steps) on the platinum surfaces. The