Development of a xylitol biosensor composed of xylitol dehydrogenase and diaphorase

In preparation for the development of a xylitol biosensor, the xylitol dehydrogenase of Candida tropicalis IFO 0618 was partially purified and characterized. The optimal pH and temperature of the xylitol dehydrogenase were pH 8.0 and 50 degrees C, respectively. Of the various alcohols tested, xylitol was the most rapidly oxidized, with sorbitol and ribitol being reduced at 65% and 58% of the xylitol rate. The enzyme was completely inactive on arabitol, xylose, glucose, glycerol, and ethanol. The enzyme's xylitol oxidation favored the use of NAD+ (7.9 U/mg) over NADP+ (0.2 U/mg) as electron acceptor, while the reverse reaction, D-xylulose reduction, favored NADPH (7.7 U/mg) over NADH (0.2 U/mg) as electron donor. The K(m) values for xylitol and NAD+ were 49.8 mM and 38.2 microM, respectively. For the generation of the xylitol biosensor, the above xylitol dehydrogenase and a diaphorase were immobilized on bromocyan-activated sephallose. The gel was then attached on a dissolved oxygen electrode. In the presence of vitamin K3, NAD+ and phosphate buffer, the biosensor recorded a linear response to xylitol concentration up to 3 mM. The reaction was stable after 15 min. When the biosensor was applied to a flow injection system, optimal operation pH and temperature were 8.0 and 30 degrees C, respectively. The strengths and limitations of the xylitol biosensor are its high affinity for NAD+, slow reaction time, narrow linear range of detection, and moderate affinity for xylitol.     

Purification and characterization of a NAD+-dependent sorbitol dehydrogenase from Japanese pear fruit

NAD+-dependent sorbitol dehydrogenase NAD-SDH, EC 1.1.1.14) from Japanese pear fruit was purified to apparent homogeneity (single band by SDS-PAGE with silver staining), and had a specific activity of 916.7 nKatal/mg protein. The molecular of the native enzyme was calculated to be 160 kDa by gel filtration, whereas SDS-PAGE gave a subunit size of 40 kDa, indicating that the native enzyme is a homotetramer. The protein immunologically reacted with an antibody raised in rabbit against the fusion protein expressed in E. coli harboring an apple NAD-SDH cDNA. The Km, values for sorbitol and fructose were 96.4+/-8.60 and 4239+/-33.5 mM, respectively, and optimum pH for sorbitol oxidation was 9.0 and 7.0 for fructose reduction. Pear NAD-SDH had a very narrow substrate specificity, that is, sorbitol, L-iditol, xylitol and L-threitol were oxidized but not any of the other alcohols tested. These data suggest the structural importance of an S configuration at C-2 and an R configuration at C-4 in the substrate(s). Its enzymatic activity was strongly inhibited both by heavy metal ions such as mercury, and by thiol compounds, such as L-cysteine. However, the addition of zinc ion reversed the enzyme inactivation caused by addition of L-cysteine.     

Catalytic mechanism of Zn2+-dependent polyol dehydrogenases: kinetic comparison of sheep liver sorbitol dehydrogenase with wild-type and Glu154-->Cys forms of yeast xylitol dehydrogenase

Co-ordination of catalytic Zn2+ in sorbitol/xylitol dehydrogenases of the medium-chain dehydrogenase/reductase superfamily involves direct or water-mediated interactions from a glutamic acid residue, which substitutes a homologous cysteine ligand in alcohol dehydrogenases of the yeast and liver type. Glu154 of xylitol dehydrogenase from the yeast Galactocandida mastotermitis (termed GmXDH) was mutated to a cysteine residue (E154C) to revert this replacement. In spite of their variable Zn2+ content (0.10-0.40 atom/subunit), purified preparations of E154C exhibited a constant catalytic Zn2+ centre activity (kcat) of 1.19+/-0.03 s(-1) and did not require exogenous Zn2+ for activity or stability. E154C retained 0.019+/-0.003% and 0.74+/-0.03% of wild-type catalytic efficiency (kcat/K(sorbitol)=7800+/-700 M(-1) x s(-1)) and kcat (=161+/-4 s(-1)) for NAD+-dependent oxidation of sorbitol at 25 degrees C respectively. The pH profile of kcat/K(sorbitol) for E154C decreased below an apparent pK of 9.1+/-0.3, reflecting a shift in pK by about +1.7-1.9 pH units compared with the corresponding pH profiles for GmXDH and sheep liver sorbitol dehydrogenase (termed slSDH). The difference in pK for profiles determined in 1H2O and 2H2O solvent was similar and unusually small for all three enzymes (approximately +0.2 log units), suggesting that the observed pK in the binary enzyme-NAD+ complexes could be due to Zn2+-bound water. Under conditions eliminating their different pH-dependences, wild-type and mutant GmXDH displayed similar primary and solvent deuterium kinetic isotope effects of 1.7+/-0.2 (E154C, 1.7+/-0.1) and 1.9+/-0.3 (E154C, 2.4+/-0.2) on kcat/K(sorbitol) respectively. Transient kinetic studies of NAD+ reduction and proton release during sorbitol oxidation by slSDH at pH 8.2 show that two protons are lost with a rate constant of 687+/-12 s(-1) in the pre-steady state, which features a turnover of 0.9+/-0.1 enzyme equivalents as NADH was produced with a rate constant of 409+/-3 s(-1). The results support an auxiliary participation of Glu154 in catalysis, and possible mechanisms of proton transfer in sorbitol/xylitol dehydrogenases are discussed.     

Relation between the oxidation state of nicotinamide–adenine dinucleotide and the metabolism of spermatozoa

1. The existing procedures for extraction of oxidized and reduced nicotinamide coenzymes were adapted to spermatozoa to overcome the coenzyme-degrading activity of seminal plasma. 2. The content of total NAD(+) and NADH was determined in the spermatozoa of ram, bull, boar, stallion and cock. NADP(+) and NADPH were not detected in ram spermatozoa. 3. The oxidation state of sperm NAD depended on the seminal plasma, the removal of which produced a change in the percentage oxidation state of the coenzyme, 100x[NAD(+)/(NAD(+)+NADH)], without altering the total content of NAD(+)+NADH. 4. In suspensions of washed ram spermatozoa, incubated anaerobically at 25 degrees C, the percentage oxidation state of NAD declined with increasing spermatozoa concentration. 5. When ram or boar spermatozoa that had been previously washed and resuspended in Ringer phosphate medium, were incubated anaerobically at 25 degrees C with various substances, pronounced effects on the percentage oxidation state of NAD could be observed with l-lactate, pyruvate, oxaloacetate, dihydroxyacetone, formaldehyde and glyceraldehyde; sorbitol and acetoacetate acted only on ram spermatozoa; fructose, glucose, mannose and acetaldehyde acted predominantly on boar spermatozoa. Formaldehyde lowered the (NAD(+)+NADH) content of ram spermatozoa, but none of the other substances had a comparable effect. 6. The percentage oxidation state of sperm NAD was not influenced by exogenous cysteine, cystine, ergothioneine or ascorbate. 7. A highly active sorbitol dehydrogenase could be prepared from ram, but not from boar, spermatozoa. 8. Sorbitol, acetoacetate and 3-hydroxybutyrate effectively supported the respiration of ram, but not boar, spermatozoa. 9. ;Cold shock', resulting from sudden cooling of spermatozoa, abolished motility completely and irreversibly but produced only a slow and partial decrease in the total NAD content. Slight over-heating, sufficient to produce loss of motility, had no adverse effect on the total NAD content. 10. Storage of ram sperm at 14 degrees C produced only a small decrease of NAD after 2 days, but subsequently the loss became greater.     

Steady-state kinetic properties of sorbitol dehydrogenase from chicken liver

The steady-state kinetic properties of partially purified chicken liver sorbitol dehydrogenase (SDH) were determined spectrophotometrically at 25 degrees C, in 50 mM 3-(N-morpholino)propanesulfonic acid (MOPS) buffer, pH 8.0. In the sorbitol-to-fructose direction, analysis was based on initial rate data obtained at [NAD(+)](o)=0.1-0.4 mM and [sorbitol](o)=1.25-10 mM. The reverse process was analyzed by recording progress curves for NADH consumption, starting with [NADH](o)=0.2 mM and [fructose](o)=66.7-267 mM. The kinetics conformed to an ordered sequential model, with the cofactors adding first. The steady-state parameters in the forward direction, K(NAD(+)), K(iNAD(+)) and K(sorbitol), were found to be 210+/-62 muM, 220+/-69 microM and 3.2+/-0.54 mM, respectively. The corresponding parameters in the reverse direction were K(NADH)=240+/-58 microM, K(iNADH)=10+/-2.8 microM and K(fructose)=1000+/-140 mM. The results indicated a close parallelism with human SDH, yet up to 40-fold differences were observed when compared to related reports on other mammalian species. The structural and adaptive bases of the variation in substrate and cofactor affinities need to be accounted for.     

Evidence that the gene YLR070c of Saccharomyces cerevisiae encodes a xylitol dehydrogenase.

The open reading frame YLR070c of Saccharomyces cerevisiae has high sequence similarity to S. cerevisiae sorbitol dehydrogenase and to xylitol dehydrogenase of Pichia stipitis. Overexpression of this open reading frame in S. cerevisiae resulted in xylitol dehydrogenase activity. The enzyme is specific for NADH. The following Michaelis constants were estimated: D-xylulose, 1.1 mM; NADH, 240 microM (at pH 7.0); xylitol, 25 mM; NAD, 100 microM (at pH 9.0). Xylitol dehydrogenase activity with the same kinetic properties can also be induced by xylose in wild type S. cerevisiae cells.     

Studies on polyol metabolism in Aspergillus niger

Summary Sorbitol dehydrogenase has been purified about 26 fold from a strain of Aspergillus niger, growing on sorbitol as the sole source of carbon. An absolute specificity of this enzyme for sorbitol, fructose, NAD and NADH was observed. The K _m for sorbitol and fructose were found to be 9.8x10^-5 M and 6.6x10^-4 M respectively. The enzyme was inhibited by pCMB, NaF and other metal ions studied. The enzyme was slightly activated by Fe⁺⁺⁺.Part of this work was presented at the All India Conference of Microbiologists held at Baroda, 1968/69.     

Purification and properties of sorbitol dehydrogenase from mouse liver

1. The sorbitol dehydrogenase (L-iditol: NAD oxidoreductase, EC 1.1.1.14) from mouse liver has been purified to homogeneity. 2. The enzyme has a mol. wt of 140,000 and is composed of four identical subunits of mol. wt 35,000. 3. the purified enzyme catalyses both sorbitol oxidation and fructose reduction. 4. It is specific for NAD+ (NADH) and does not function with NADP+ (NADPH). 5. The Michaelis constants for sorbitol, fructose, NAD+ and NADPH are 1.54 and 154 mM, 58.8 and 15 microM, respectively. 6. The enzyme is SH-group reagent sensitive and is strongly inhibited by 1,10-phenanthroline.     

Kinetic study of the catalytic mechanism of mannitol dehydrogenase from Pseudomonas fluorescens.

To characterize catalysis by NAD-dependent long-chain mannitol 2-dehydrogenases (MDHs), the recombinant wild-type MDH from Pseudomonas fluorescens was overexpressed in Escherichia coli and purified. The enzyme is a functional monomer of 54 kDa, which does not contain Zn(2+) and has B-type stereospecificity with respect to hydride transfer from NADH. Analysis of initial velocity patterns together with product and substrate inhibition patterns and comparison of primary deuterium isotope effects on the apparent kinetic parameters, (D)k(cat), (D)(k(cat)/K(NADH)), and (D)(k(cat)/K(fructose)), show that MDH has an ordered kinetic mechanism at pH 8.2 in which NADH adds before D-fructose, and D-mannitol and NAD are released in that order. Isomerization of E-NAD to a form which interacts with D-mannitol nonproductively or dissociation of NAD from the binary complex after isomerization is the slowest step (>/=110 s(-)(1)) in D-fructose reduction at pH 8.2. Release of NADH from E-NADH (32 s(-)(1)) is the major rate-limiting step in mannitol oxidation at this pH. At the pH optimum for D-fructose reduction (pH 7.0), the rate of hydride transfer contributes significantly to rate limitation of the catalytic cascade and the overall reaction. (D)(k(cat)/K(fructose)) decreases from 2.57 at pH 7.0 to a value of 相似文献   

Zymomonas mobilis mutants blocked in fructose utilization

Summary A mutant ofZymomonas mobilis deficient in the utilization of fructose for growth and ethanol formation was shown to lack fructokinase activity. When grown in media which contained glucose+fructose or sucrose, both the mutant and wild type produced sorbitol in amounts up to 60 g·l^-1, depending on the initial concentrations of sugars. Sorbitol formation was accompanied by an accumulation of acetaldehyde, gluconate, and acetoin. A ferricyanide-dependent sorbitol dehydrogenase could be localized in the cell membrane; it thus resembles the sorbitol dehydrogenase ofGluconobacter suboxydans. Neither a NAD(P)H dependent reduction of fructose nor a NAD(P) dependent dehydrogenation of sorbitol could be detected in cell-free extracts. The use of fructose-negative mutants ofZ. mobilis for the enrichment of fructose in glucose+fructose mixtures is discussed.     

Biochemical characteristics of erythrocyte sorbitol dehydrogenase from selected mammals

The erythrocyte sorbitol dehydrogenase (EC 1.1.1.14) activity, regarding its action on sorbitol oxidation to fructose, was studied in 19 species of mammals, showing a striking variability, with high activity in rodents. Enzyme activity was studied against other polyols, namely xylitol, inositol, manitol and dulcitol. Most animals showed activity against all the polyols studied, but hamster and red deer only presented activity on sorbitol and xylitol. Michaelis-Menten constant determinations for sorbitol were performed, and it was observed that animals which presented high activity had a high Km. pH curves were obtained from 8 animals, with an optimum pH ranging from pH 8.0 to pH 10.0; four of the animals presented an optimum pH at 8.5.     

The reversibility of cytosolic dehydrogenase reactions in hepatocytes from starved and fed rats. Effect of fructose.

The metabolism of [2-3H]lactate was studied in isolated hepatocytes from fed and starved rats metabolizing ethanol and lactate in the absence and presence of fructose. The yields of 3H in ethanol, water, glucose and glycerol were determined. The rate of ethanol oxidation (3 mumol/min per g wet wt.) was the same for fed and starved rats with and without fructose. From the detritiation of labelled lactate and the labelling pattern of ethanol and glucose, we calculated the rate of reoxidation of NADH catalysed by lactate dehydrogenase, alcohol dehydrogenase and triosephosphate dehydrogenase. The calculated flux of reducing equivalents from NADH to pyruvate was of the same order of magnitude as previously found with [3H]ethanol or [3H]xylitol as the labelled substrate [Vind & Grunnet (1982) Biochim. Biophys. Acta 720, 295-302]. The results suggest that the cytoplasm can be regarded as a single compartment with respect to NAD(H). The rate of reduction of acetaldehyde and pyruvate was correlated with the concentration of these metabolites and NADH, and was highest in fed rats and during fructose metabolism. The rate of reoxidation of NADH catalysed by lactate dehydrogenase was only a few per cent of the maximal activity of the enzymes, but the rate of reoxidation of NADH catalysed by alcohol dehydrogenase was equal to or higher than the maximal activity as measured in vitro, suggesting that the dissociation of enzyme-bound NAD+ as well as NADH may be rate-limiting steps in the alcohol dehydrogenase reaction.     

Purification and Properties of NAD-Dependent Sorbitol Dehydrogenase from Apple Fruit

This is the first report of the purification of NAD-dependentsorbitol dehydrogenase (NAD-SDH) from a plant source. The enzymewas extracted from apple (Malus domestica cv. Ourin) fruit andpurified until it appeared as a single polypeptide chain ona gel after SDS-PAGE. From the apparent molecular mass of 62kDa obtained by SDS-PAGE and that of 120 kDa by gel filtration,the enzyme appeared to be a homodimer. Maximum rates of oxidationof sorbitol and reduction of fructose were observed at pH 9.6and pH 6.0, respectively. The K_m for oxidation of sorbitol was40.3 mM and that for reduction of fructose was 215 mM. The maximumrate of oxidation of sorbitol was about 10 times higher thanthat of the reduction of fructose. The results of the kineticanalysis strongly suggest that in vivo the enzyme would favorthe conversion of sorbitol to fructose over the reverse reaction.None of the divalent cations tested had any effect on the oxidationof sorbitol by NAD-SDH. The reaction catalyzed by NAD-SDH wasnot specific to sorbitol and other substrates could also beoxidized. Among the tested substrates, ethyl alcohol had a particularlyhigh affinity for the enzyme. (Received February 2, 1994; Accepted May 31, 1994)     

NAD(H) enhances the Cu(II)-mediated inactivation of lactate dehydrogenase by increasing the accessibility of sulfhydryl groups

Copper ions are known to inactivate a variety of enzymes, and lactate dehydrogenase (LDH) is exceptionally sensitive to the presence of this metal. We now found that NADH strongly enhances the Cu(II)-mediated loss of LDH activity. Surprisingly, NADH was not oxidized in this process and also NAD⁺ promoted the Cu(II)-dependent inactivation of LDH. Catalase only partly protected the enzyme, whereas hypoxia even enhanced LDH inactivation. NAD(H) accelerated sulfhydryl (SH) group oxidation of LDH by 5,5-dithio-bis(2-nitrobenzoic acid) (DTNB), and, vice versa, LDH-mediated Cu(II) reduction. LDH activity was preserved by thiol donators and pyruvate and partially preserved by lactate and oxamate. Our results suggest that reactive oxygen species (ROS) are of minor importance for the inactivation of LDH induced by Cu(II)/NADH. We propose that conformational changes of the enzymes' active sites induced by NAD(H)-binding increase the accessibility of active sites' cysteine residues to Cu(II) thereby accelerating their oxidation and, consequently, loss of catalytic activity.     

Partial purification and characterization of mannitol: mannose 1-oxidoreductase from celeriac (Apium graveolens var. rapaceum) roots.

A mannitol:mannose 1-oxidoreductase was isolated from celeriac (Apium graveolens var. rapaceum) root tips by fractionation with (NH4)2SO4, followed by chromatography on a Fractogel DEAE column and then concentration with (NH4)2SO4. This newly discovered mannitol dehydrogenase catalyzes the NAD-dependent oxidation of mannitol to mannose, not mannitol to fructose. The sugar product of the enzyme reaction was identified by three independent HPLC systems and by an enzymatically linked system as being mannose and not fructose or glucose. Normal Michaelis--Menten kinetics were exhibited for both mannitol and NAD with Km values of 72 and 0.26 mM, respectively, at pH 9.0. The Vmax was 40.14 mumol/h/mg protein for mannitol synthesis and 0.8 mumol/h/mg protein for mannose synthesis at pH 9.0. In the polyol oxidizing reaction, the enzyme was very specific for mannitol with a low rate of oxidation of sorbitol. In the reverse reaction, the enzyme was specific for mannose. The enzyme was strongly inhibited by NADH and sensitive to alterations of NAD/NADH ratio. The enzyme is of physiological importance in that it is mainly localized in root tips (sink tissue) where it functions to convert mannitol into hexoses which are utilized to support root growth. Product determination and kinetic characterization were carried out on an enzyme preparation with a specific activity (SA) of 30.44 mumol/h/mg protein. Subsequently, the enzyme was further purified to a SA of 201 mumol/h/mg protein using an NAD affinity column. This paper apparently represents the first evidence of the existence of a mannitol:mannose 1-oxidoreductase and also the first evidence of the presence of a mannitol dehydrogenase in vascular plants.     

Purification and characterization of human liver sorbitol dehydrogenase

Sorbitol dehydrogenase from human liver was purified to homogeneity by affinity chromatography on immobilized triazine dyes, conventional cation-exchange chromatography, and high-performance liquid chromatography. The major form is a tetrameric, NAD-specific enzyme containing one zinc atom per subunit. Human liver sorbitol dehydrogenase oxidizes neither ethanol nor other primary alcohols. It catalyzes the oxidation of a secondary alcohol group of polyol substrates such as sorbitol, xylitol, or L-threitol. However, the substrate specificity of human liver sorbitol dehydrogenase is broader than that of the liver enzymes of other sources. The present report describes the stereospecific oxidation of (2R,3R)-2,3-butanediol, indicating a more general function of sorbitol dehydrogenase in the metabolism of secondary alcohols. Thus, the enzyme complements the substrate specificities covered by the three classes of human liver alcohol dehydrogenase.     

Membrane-bound sugar alcohol dehydrogenase in acetic acid bacteria catalyzes L-ribulose formation and NAD-dependent ribitol dehydrogenase is independent of the oxidative fermentation

To identify the enzyme responsible for pentitol oxidation by acetic acid bacteria, two different ribitol oxidizing enzymes, one in the cytosolic fraction of NAD(P)-dependent and the other in the membrane fraction of NAD(P)-independent enzymes, were examined with respect to oxidative fermentation. The cytoplasmic NAD-dependent ribitol dehydrogenase (EC 1.1.1.56) was crystallized from Gluconobacter suboxydans IFO 12528 and found to be an enzyme having 100 kDa of molecular mass and 5 s as the sedimentation constant, composed of four identical subunits of 25 kDa. The enzyme catalyzed a shuttle reversible oxidoreduction between ribitol and D-ribulose in the presence of NAD and NADH, respectively. Xylitol and L-arabitol were well oxidized by the enzyme with reaction rates comparable to ribitol oxidation. D-Ribulose, L-ribulose, and L-xylulose were well reduced by the enzyme in the presence of NADH as cosubstrates. The optimum pH of pentitol oxidation was found at alkaline pH such as 9.5-10.5 and ketopentose reduction was found at pH 6.0. NAD-Dependent ribitol dehydrogenase seemed to be specific to oxidoreduction between pentitols and ketopentoses and D-sorbitol and D-mannitol were not oxidized by this enzyme. However, no D-ribulose accumulation was observed outside the cells during the growth of the organism on ribitol. L-Ribulose was accumulated in the culture medium instead, as the direct oxidation product catalyzed by a membrane-bound NAD(P)-independent ribitol dehydrogenase. Thus, the physiological role of NAD-dependent ribitol dehydrogenase was accounted to catalyze ribitol oxidation to D-ribulose in cytoplasm, taking D-ribulose to the pentose phosphate pathway after being phosphorylated. L-Ribulose outside the cells would be incorporated into the cytoplasm in several ways when need for carbon and energy sources made it necessary to use L-ribulose for their survival. From a series of simple experiments, membrane-bound sugar alcohol dehydrogenase was concluded to be the enzyme responsible for L-ribulose production in oxidative fermentation by acetic acid bacteria.     

Purification and properties of beta-hydroxybutyrate dehydrogenase from Mycobacterium phlei ATCC354.

beta-Hydroxybutyrate dehydrogenase (EC 1.1.1.30) was purified 145-fold from Mycobacterium phlei ATCC354 by ammonium sulphate fractionation and DEAE-cellulose chromatography. The pH optima for oxidation and reduction reactions were 8.4 and 6.8 respectively. The purified enzyme was specific for NAD, NADH, acetoacetate and D(-)-beta-hydroxybutyrate. Km values for DL-beta-hydroxybutyrate and NAD were 7.4 mM and 0.66 mM respectively. The enzyme was inactivated by mercurial thiol inhibitors and by heat, but could be protected by NADH, Ca2+ and partially by Mn2+. The enzyme did not require metal ions and was insensitive to EDTA, glutathione, dithiothreitol, beta-mercaptoethanol and cysteine.     

Membrane-Associated NAD-Dependent Isocitrate Dehydrogenase in Potato Mitochondria

The oxidation isotherms for citrate and isocitrate by potato (Solanum tuberosum var. Russet Burbank) mitochondria in the presence of NAD differ markedly. Citrate oxidation shows positively cooperative kinetics with a sigmoid isotherm, whereas isocitrate oxidation shows Michaelis-Menten kinetics at concentrations up to 3 millimolar, and cooperative kinetics thereafter up to 30 millimolar. In the absence of exogenous NAD, the isocitrate isotherm is sigmoid throughout. The dual isotherm for isocitrate oxidation in the presence of exogenous NAD reflects the operation of two forms of isocitrate dehydrogenase, one in the matrix and one associated with the inner mitochondrial membrane. Whereas in intact mitochondria the activity of the membrane-bound enzyme is insensitive to rotenone, and to butylmalonate, an inhibitor of organic acid transport, isocitrate oxidation by the soluble matrix enzyme is inhibited by both. The membrane-bound isocitrate dehydrogenase does not operate through the NADH dehydrogenase on the outer face of the inner mitochondrial membrane, and is thus considered to face inward. The regulatory potential of isocitrate dehydrogenase in potato mitochondria may be realized by the apportionment of the enzyme between its soluble and bound forms.