Alcohol Dehydrogenase Enzyme Activity Research Articles

The role of PME and ADH enzymes in seed deterioration and its implication for producing high quality soybean seed

Soybean seeds are member of the orthodox seeds group which suseptable to deterioration. The low quality of soybean seeds used by farmers is one of the causes of the low soybean productivity at the farmer level. Pectin methylesterase (PME) and alcohol dehydrogenase (ADH) enzymes have been studied in relation to seed deterioration. Increase in seed moisture content is strongly suspected to be the initial occurrence and increase in PME enzyme activity which then followed by ADH enzyme activity in a series of biochemical reactions leading to the accumulation of acetaldehyde-protein adducts (APA) in soybean seeds. The APA contributes to deterioration of seeds. Thus, the increase in APA in soybean seeds may be used as an indicator of the level of deterioration of soybean seeds. Since high seed moisture content contributes to the initiation of PME activity in seeds, soybean seed production in the rainy season is not recommended because it will produce seeds with low physiological quality due to high PME activity so that the seeds cannot be stored for long-term period.

Waterlogging Tolerance of Actinidia valvata Dunn Is Associated with High Activities of Pyruvate Decarboxylase, Alcohol Dehydrogenase and Antioxidant Enzymes.

Kiwifruit (Actinidia spp.) is susceptible to waterlogging stress. Although abundant wild germplasm resources exist among Actinidia plants for improving the waterlogging tolerance of kiwifruit cultivars, the underlying mechanisms remain largely unknown. Here, a comparative study was undertaken using one wild germplasm, Maorenshen (A. valvata Dunn, MRS), and one cultivar, Miliang-1 (A. chinensis var. deliciosa (A.Chev.) A.Chev. cv. Miliang-1, ML). Under stress, the ML plantlets were seriously damaged with wilted chlorotic leaves and blackened rotten roots, whereas the symptoms of injury in the MRS plantlets were much fewer, along with higher photosynthetic rates, chlorophyll fluorescence characteristics and root activity under stress conditions. However, neither aerenchyma in the root nor adventitious roots appeared in both germplasms upon stress exposure. The activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH), as well as their transcript levels, were constitutively higher in MRS than those in ML under both normal and stress conditions. Waterlogging stress significantly enhanced the PDC and ADH enzyme activities in both germplasms, which were 60.8% and 22.4% higher in the MRS roots than those in the ML roots under waterlogging stress, respectively. Moreover, MRS displayed higher activities of antioxidant enzymes, including SOD, CAT, and APX, as well as DPPH-radical scavenging ability, and decreased H2O2 and MDA accumulation under both normal and stress conditions. Our findings suggest that the waterlogging tolerance of the wild A. valvata germplasm was associated with high PDC and ADH, as well as antioxidant ability.

Luminescent Sensor Based on Ln(III) Ternary Complexes for NAD(P)H Detection.

Ln(III) complexes of macrocyclic ligands are used in medicinal chemistry, for example as contrast agents in MRI or radiopharmaceutical compounds, and in diagnostics using fluorescence imaging. This paper is devoted to a spectroscopic study of Ln(III) ternary complexes consisting of macrocyclic heptadentate DO3A and bidentate 3-isoquinolinate (IQCA) ligands. IQCA serves as an efficient antenna ligand, leading to a higher quantum yield and Stokes shift (250–350 nm for Eu, Tb, Sm, Dy in VIS region, 550–650 nm for Yb, Nd in NIR region). The shielding-quenching effect of NAD(P)H on the luminescence of the Ln(III) ternary complexes was investigated in detail and this phenomenon was utilized for the analytical determination of this compound. This general approach was verified through an enzymatic reaction during which the course of ethanol transformation catalyzed by alcohol-dehydrogenase (ADH) was followed by luminescence spectroscopy. This method can be utilized for selective and sensitive determination of ethanol concentration and/or ADH enzyme activity. This new analytical method can also be used for other enzyme systems coupled with NAD(P)H/NAD(P)+ redox pairs.

Specific ion effects on the enzymatic activity of alcohol dehydrogenase from Saccharomyces cerevisiae.

The enzymatic activity of alcohol dehydrogenase (ADH) in the presence of a range of electrolytes is investigated. In the presence of 150 and 200 mM cations a substantial increase in activity following the series GnCl < CsCl < KCl ∼ NaCl < LiCl was observed with a 69% increase in the presence of KCl 200 mM with respect to the salt-free solution. In the presence of 150 and 200 mM anions the increase in activity followed an ion specific trend NaF ∼ NaCl ∼ NaBr > no salt > NaClO4 > NaSCN with a peak in activity increase of 75% in the presence of NaBr. The values of the Michaelis-Menten constant (Km) did not show any significant ion specific effect, while the maximum rate (Vmax) of ethanol oxidation to acetaldehyde was strongly ion specific. The changes in specific activity and Vmax in the presence of anions likely arises from ion specific interactions with charged residues in the active site of ADH. The data indicate that the enzymatic activity of alcohol dehydrogenase can be modulated by the nature of electrolytes at physiological concentration.

Influence of food commodities on hangover based on alcohol dehydrogenase and aldehyde dehydrogenase activities

Alcohol consumption often leads to hangover, a condition characterized by several symptoms, characteristically headache, nausea, fatigue and drowsiness. Hangover may be alleviated by altering the rate of alcohol metabolism and facilitating elimination of acetaldehyde by affecting the activity of alcohol dehydrogenase (ADH) and/or aldehyde dehydrogenase (ALDH) enzymes. In the present study, several food commodities like fruits, vegetables, cereals, pulses, dairy products, spices and other miscellaneous products (ascorbic acid, cocoa sample, tea, coffee, egg yolk and date samples) were investigated for their effect on the in vitro activities of the enzymes and their antioxidant properties. Of the many screened food commodities, few showed an increase in the activity of either one or both the enzymes, ADH and ALDH. Studies showed no correlation between ADH and ALDH enzyme activities and antioxidant property of the selected food commodities for anti-hangover effect. Further, an anti-hangover (AHO) product was developed using pear (65%), sweet lime (25%) and coconut water (10%) and, validated for in vitro ADH and ALDH enzyme activities. AHO product was found to enhance ADH and ALDH activities by 23.31% and 70.02%, respectively.

High-pressure study of magnetic nanoparticles with a polyelectrolyte brush as carrier particles for enzymes

The recovery of enzymes from a reaction medium can be achieved in a convenient way by using magnetic nanoparticles (MNP) as carriers. Here, we present MNP with a polyelectrolyte brush composed of poly(ethylene imine) (PEI) to provide a benign environment for the immobilized enzyme molecules. Yeast alcohol dehydrogenase (ADH) has been tested for enzymatic activity when it is free in solution or adsorbed on the PEI brush-MNP. Furthermore, the effect of pressure on the enzymatic activity has been studied to reveal activation volumes, which are a sensitive probe of the transition state geometry. The results of this study indicate that the secondary structure of ADH is pressure-stable up to 9 kbar. The enzymatic activity of ADH can be analyzed using Michaelis–Menten kinetics free in solution and adsorbed on the PEI brush-MNP. Remarkably, no significant changes of the Michaelis constant and the activation volume are observed upon adsorption. Thus, it can be assumed that the turnover number of ADH is also the same in the free and adsorbed state. However, the maximum enzymatic rate is reduced when ADH is adsorbed, which must be explained by a lower effective enzyme concentration due to steric hindrance of the enzyme inside the PEI brush of the MNP. In this way, the pressure experiments carried out in this study enable a distinction between steric and kinetic effects on the enzymatic rate of adsorbed ADH.

Temperature-induced recovery of a bioactive enzyme using polyglycerol dendrimers: correlation between bound water and protein interaction

Enzyme application has gained importance over the past decade in bioprocess, biomedical, and pharmaceutical fields. We found that polyglycerol dendrimers (PGDs), which are biocompatible molecules, can recover alcohol dehydrogenase (ADH) from aqueous solution under elevated temperature. A low concentration of PGD (5 wt.%) is sufficient for the recovery of high enzymatic activity, although a high concentration (25–75 wt.%) of glycerol is generally required to stabilize ADH. The enzymatic activity of ADH in suspension with PGDs is over 60% but it is only 10% in that with glycerol. The results of osmolarity and spin-lattice relaxation time (T1) of water measurements in the presence of PGDs suggest that increased amounts of bound water to PGD molecules trigger aggregation along with the direct interaction with ADH. PGDs therefore represent good potential additives for direct recovery of enzymes from aqueous solutions.

RecET recombination system driving chromosomal target gene replacement in Zymomonas mobilis

Background: Zymomonas mobilis is a Gram-negative microaerophilic bacterium with excellent ethanol-producing capabilities. The RecET recombination system provides an efficient tool for direct targeting of genes in the bacterial chromosome by PCR fragments. Results: The plasmids pSUZM2a-RecET and pSUZM2a-RecE588T were first developed to co-express RecE or RecE588 and RecT for homologous recombination. Thereafter, the PCR fragments of the tetracycline resistance marker gene flanked by 60 bp of adhA (alcohol dehydrogenase I) or adhB (alcohol dehydrogenase II) homologous sequences were electroporated directly into ZM4 cells harboring pSUZM2a-RecET or pSUZM2a-RecE588T. Both adhA and adhB were replaced by the tetracycline resistance gene in ZM4, yielding two mutant strains, Z. mobilis ZM4 Δ adhA and Z. mobilis ZM4 Δ adhB . These two mutants showed varying extent of reduction in ethanol production, biomass generation, and glucose metabolism. Furthermore, enzyme activity of alcohol dehydrogenase II in Z. mobilis ZM4 Δ adhB exhibited a significant reduction compared to that of wild-type ZM4. Conclusion: This approach provided a simple and useful method for introducing mutations and heterologous genes in the Z. mobilis genome. Normal 0 false false false ES-CL X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:8.0pt; mso-para-margin-left:0cm; line-height:107%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Times New Roman; mso-bidi-theme-font:minor-bidi; mso-ansi-language:ES-CL;}

Analysis of Enzyme Activity of Alcohol Dehydrogenase and Alcohol Dehydrogenase 3 (ADH3) Gene Polymorphism of Alcoholics and Non-Alcoholics in Indonesia

ABSTRACT Alcohol is an addictive substance that is often misused worldwide, including in Indonesia. Ninety percent of the alcohol that enters the body will be metabolized in the liver using the alcohol dehydrogenase (ADH) enzyme. It is important to determine the activity of ADH enzyme and ADH3 gene polymorphism on alcoholics and non-alcoholics in Yogyakarta, Indonesia. The aim of the study is to determine ADH activity and identify ADH3 gene polymorphism of alcoholics and non-alcoholics in Yogyakarta, Indonesia. This study was an observational study with a cross-sectional design method. Blood samples were taken from 71 Javanese alcoholics and 71 non-alcoholics of Javanese descent in Yogyakarta, Indonesia. The participants were initially requested to sign an informed consent form. Examination of ADH enzyme activity used the spectrophotometry method and ADH3 gene polymorphism was assessed with PCR-RFLP using Ssp I restriction enzyme. The activity of ADH enzyme in all individuals appeared to be a slower type. The average of the ethanol value of alcoholics and non-alcoholics were 0.05554 mM and 0.0758 mM respectively. Gene type of alcoholics were ADH3*2(75.4%), ADH3*1/3*2(21.5%), and ADH3*1(3.1%), and non-alcoholics were ADH3*2(88.6%), ADH3*1/3*2(10.0%), and ADH3*1(1.4%). There were no significant differences between the activity of ADH with polymorphism of ADH3 gene in either alcoholics and non-alcoholics (p>0,05). Conclusion: The activity of ADH enzyme in all participants appeared to be a slower type. Most of the ADH3 gene polymorphism of alcoholics and non-alcoholics were both ADH3*2 (75.4% and 88.6%). There was no differences of ADH enzyme activity with ADH3 gene polymorphism between alcoholics and non-alcoholics of Javanese population in Yogyakarta, Indonesia.

The Alcohol Dehydrogenase Kinetics Laboratory: Enhanced Data Analysis and Student-Designed Mini-Projects

A highly instructive, wide-ranging laboratory project in which students study the effects of various parameters on the enzymatic activity of alcohol dehydrogenase has been adapted for the upper-division biochemistry and physical biochemistry laboratory. Our two main goals were to provide enhanced data analysis, featuring nonlinear regression, and also to give students experience in experimental design. Students use appropriate kinetic and thermodynamic equations to fit their data from Michaelis–Menten plots, enzyme activity pH profiles, inhibitor and denaturant concentration profiles, and temperature-dependence plots. Experiments at the end of this project are designed and implemented by student pairs, thus preparing them for independent research.

Encapsulation of Alcohol Dehydrogenase in Mannitol by Spray Drying

The retention of the enzyme activity of alcohol dehydrogenase (ADH) has been studied in various drying processes such as spray drying. The aim of this study is to encapsulate ADH in mannitol, either with or without additive in order to limit the thermal denaturation of the enzyme during the drying process. The retention of ADH activity was investigated at different drying temperatures. When mannitol was used, the encapsulated ADH was found inactive in all the dried powders. This is presumably due to the quick crystallization of mannitol during spray drying that resulted in the impairment of enzyme protection ability in comparison to its amorphous form. Maltodextin (dextrose equivalent = 11) was used to reduce the crystallization of mannitol. The addition of maltodextrin increased ADH activity and drastically changed the powder X-ray diffractogram of the spray-dried powders.

Enzyme immobilization by fouling in ultrafiltration membranes: Impact of membrane configuration and type on flux behavior and biocatalytic conversion efficacy

Enzyme-immobilization in membranes accomplished by fostering membrane fouling was evaluated. Four different membrane configurations and five membranes were compared for immobilization of alcohol dehydrogenase (ADH) in terms of enzyme loading, permeate flux and final biocatalytic conversion. The membrane configuration impacted the efficiency of the enzyme-immobilization as well as the biocatalytic-membrane reaction, and the “sandwich mode”, with an extra polypropylene support above the membrane skin layer, worked best due to its high flux and stable conversion. Among the membranes, a GR51PP polysulphone membrane allowed for the highest flux during the reaction with the enzyme-immobilized membrane. At the same time, the lowest enzyme loading and low reaction stability were achieved for this membrane. Satisfactory enzyme loadings, stable conversions, but low flux rates were obtained for the PLTK and PLGC regenerated cellulose membranes. With these two highly hydrophilic membranes, the ADH enzyme activity was fully retained even after 24h of storage of the membrane. Filtration blocking and resistance models were used to analyze the fouling/immobilization mechanisms and give explanations for the different results. The work confirms that fouling-induced enzyme immobilization is a promising option for enhancing biocatalytic productivity, and highlights the significance of the membrane type and configuration for optimal performance.

Effects of 1-methylcyclopropene on the Metabolic Pathways of Aroma-Related Compounds in Nanguo Pear

The aroma of Nanguo pear directly impacts its quality. This study investigated effects of 1-methylcyclopropene treatment on aroma metabolic pathway of Nanguo pear (Pyrus ussuriensis Maxim.). Nanguo pear were treated with 0.75 μL/L 1-methylcyclopropene for 24 h at 20C immediately after harvesting, and placed at room temperature for 7 days, and then refrigerated at 0 ± 0.5C for 3 and 5 months. The control fruits (without treatment) were stored under similar conditions. Results showed that 1-methylcyclopropene treatment decreased fatty acid content and reduced activity of lipoxygenase, hydrogen peroxide repressible enzyme, pyruvate decarboxylase and alcohol acyltransferase but had no significant effect on alcoholdehydrogenase enzyme activity. The total amino acid content was higher and ester content was lower in treated fruits compared to untreated fruits. This indicates that effect of 1-methylcyclopropene is via fatty acid biosynthesis pathway and inhibition of activity of lipoxygenase, hydrogen peroxide repressible enzyme, pyruvate decarboxylase and alcohol acyltransferase. Practical Applications The treatment of Nanguo pear fruit with 1-methylcyclopropene combined with refrigeration could effectively improve the quality of the commodity during the preservation at room temperature after refrigeration. Our paper investigated the effects of 1-methylcyclopropene on the metabolic pathways of aroma-related compounds in Nanguo pear and revealed the reason for the reduction of the volatile compounds. In addition, this study provides the basis to resolve the issue of reduction of aroma quality in preserved Nanguo pear.

Fermentative 2‐carbon metabolism produces carcinogenic levels of acetaldehyde in Candida albicans

Acetaldehyde is a carcinogenic product of alcohol fermentation and metabolism in microbes associated with cancers of the upper digestive tract. In yeast acetaldehyde is a by-product of the pyruvate bypass that converts pyruvate into acetyl-Coenzyme A (CoA) during fermentation. (i) to determine the levels of acetaldehyde produced by Candida albicans in the presence of glucose in low oxygen tension in vitro; (ii) to analyse the expression levels of genes involved in the pyruvate-bypass and acetaldehyde production; and (iii) to analyse whether any correlations exist between acetaldehyde levels, alcohol dehydrogenase enzyme activity or expression of the genes involved in the pyruvate-bypass. Candida albicans strains were isolated from patients with oral squamous cell carcinoma (n=5), autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients with chronic oral candidosis (n=5), and control patients (n=5). The acetaldehyde and ethanol production by these isolates grown under low oxygen tension in the presence of glucose was determined, and the expression of alcohol dehydrogenase (ADH1 and ADH2), pyruvate decarboxylase (PDC11), aldehyde dehydrogenase (ALD6) and acetyl-CoA synthetase (ACS1 and ACS2) and Adh enzyme activity were analysed. The C.albicans isolates produced high levels of acetaldehyde from glucose under low oxygen tension. The acetaldehyde levels did not correlate with the expression of ADH1, ADH2 or PDC11 but correlated with the expression of down-stream genes ALD6 and ACS1. Significant differences in the gene expressions were measured between strains isolated from different patient groups. Under low oxygen tension ALD6 and ACS1, instead of ADH1 or ADH2, appear the most reliable indicators of candidal acetaldehyde production from glucose.

Application of reduced graphene oxide and carbon nanotube modified electrodes for measuring the enzymatic activity of alcohol dehydrogenase

An electrochemical method was developed to measure the enzymatic activity of alcohol dehydrogenase (ADH) by monitoring the amount of reduced nicotinamide adenine dinucleotide (NADH) generated in the catalysed oxidation of ethanol by ADH. The concentration of NADH was determined by amperometric measurements, which recorded the oxidation current of NADH versus time on reduced graphene oxide and functionalised multi-walled carbon nanotube modified electrodes. The initial reaction rates and the apparent Michaelis constants of the enzymatic reaction were obtained in the absence and presence of Al3+ and nanometre-sized tridecameric aluminium polycationic (nano-Al13) species. The results showed that Al3+ and nano-Al13 exhibited inhibitory effect on the enzymatic activity of ADH. Fluorescence and circular dichroism spectra indicated the inhibitory effect was likely caused by the conformational changes of ADH and/or NADH induced by Al3+ and nano-Al13.

Regulation of enzyme activity of alcohol dehydrogenase through its interactions with pyruvate-ferredoxin oxidoreductase in Thermoanaerobacter tengcongensis

Alcohol dehydrogenases (ADHs) from thermophilic microorganisms are interesting enzymes that have their potential applications in biotechnology and potentially provide insight into the mechanisms of action of thermo-tolerant proteins. The molecular mechanisms of ADHs under thermal stress in vivo have yet to be explored. Herein, we employed a proteomic strategy to survey the possible interactions of secondary-ADH (2-ADH) with other proteins in Thermoanaerobacter tengcongensis (T. tengcongensis) cultured at 75°C and found that 2-ADH, pyruvate-ferredoxin oxidoreductase (PFOR) and several glycolytic enzymes coexisted in a protein complex. Using anion exchange chromatography, the elution profile indicated that the native 2-ADH was present in two forms, PFOR-bound and PFOR-free. Immuno-precipitation and pull down analysis further validated the interactions between 2-ADH and PFOR. The kinetic behaviours of 2-ADH either in the recombinant or native form were evaluated with different substrates. The enzyme activity of 2-ADH was inhibited in a non-competitive mode by PFOR, implying the interaction of 2-ADH and PFOR negatively regulated alcohol formation. In T. tengcongensis, PFOR is an enzyme complex located at the upstream of 2-ADH in the alcohol generation pathway. These findings, therefore, offered a plausible mechanism for how alcohol metabolism is regulated by hetero-interactions between 2-ADH and PFOR, especially in anaerobic thermophiles.

Temperature and water loss affect ADH activity and gene expression in grape berry during postharvest dehydration

Clusters of Aleatico wine grape were picked at 18°Brix and placed at 10, 20, or 30°C, 45% relative humidity (RH) and 1.5m/s of air flow to dehydrate the berries up to 40% of loss of initial fresh weight. Sampling was done at 0%, 10%, 20%, 30%, and 40% weight loss (wl). ADH (alcohol dehydrogenase) gene expression, enzyme activity, and related metabolites were analysed. At 10°C, acetaldehyde increased rapidly and then declined, while ethanol continued to rise. At 20°C, acetaldehyde and ethanol increased significantly with the same pattern and declined at 40%wl. At 30°C, acetaldehyde did not increase but ethanol increased rapidly already at 10%wl. At the latter temperature, a significant increase in acetic acid and ethyl acetate occurred, while at 10°C their values were low. At 30°C, the ADH activity (ethanol to acetaldehyde direction), increased rapidly but acetaldehyde did not rise because of its oxidation to acetic acid, which increased together with ethyl acetate. At 10°C, the ADH activity increased at 20%wl and continued to rise even at 40%wl, meaning that ethanol oxidation was delayed. At 20°C, the behaviour was intermediate to the other temperatures.The relative expression of the VvAdh2 gene was the highest at 10°C already at 10%wl in a synchrony with the ADH activity, indicating a rapid response likely due to low temperature. The expression subsequently declined. At 20 and 30°C, the expression was lower and increased slightly during dehydration in combination with the ADH activity. This imbalance between gene expression and ADH activity at 10°C, as well as the unexpected expression of the carotenoid cleavage dioxygenase 1 (CCD1) gene, opens the discussion on the stress sensitivity and transcription event during postharvest dehydration, and the importance of carefully monitoring temperature during dehydration.

Switching Clostridium acetobutylicum to an ethanol producer by disruption of the butyrate/butanol fermentative pathway

Solventogenic clostridia are well-known since almost a century due to their unique capability to biosynthesize the solvents acetone and butanol. Based on recently developed genetic engineering tools, a targeted 3-hydroxybutyryl-CoA dehydrogenase (Hbd)-negative mutant of Clostridium acetobutylicum was generated. Interestingly, the entire butyrate/butanol (C 4) metabolic pathway of C. acetobutylicum could be inactivated without a severe growth limitation and indicated the general feasibility to manipulate the central fermentative metabolism for product pattern alteration. Cell extracts of the mutant C. acetobutylicum hbd::int(69) revealed clearly reduced thiolase, Hbd and crotonase but increased NADH-dependent alcohol dehydrogenase enzyme activities as compared to the wildtype strain. Neither butyrate nor butanol were detected in cultures of C. acetobutylicum hbd::int(69), and the formation of molecular hydrogen was significantly reduced. Instead up to 16 and 20 g/l ethanol were produced in glucose and xylose batch cultures, respectively. Further sugar addition in glucose fed-batch fermentations increased the ethanol production to a final titer of 33 g/l, resulting in an ethanol to glucose yield of 0.38 g/g.

Xylitol inhibits carcinogenic acetaldehyde production byCandidaspecies

Acetaldehyde is a highly toxic and mutagenic product of alcohol fermentation and metabolism which has been classified as a Class I carcinogen for humans by the International Agency for Research on Cancer of the World Health Organisation (WHO). Many Candida species representing oral microbiota have been shown to be capable of marked acetaldehyde production. The aim of our study was to examine the effects of various sugar alcohols and sugars on microbial acetaldehyde production. The study hypothesis was that xylitol could reduce the amount of acetaldehyde produced by Candida. Laboratory and clinical isolates of seven Candida species were selected for the study. The isolates were incubated in 12 mM ethanol and 110 mM glucose, fructose or xylitol at 37°C for 30 min and the formed acetaldehyde was measured by gas chromatography. Xylitol significantly (p < 0.0001) reduced the amount of acetaldehyde produced from ethanol by 84%. In the absence of xylitol, the mean acetaldehyde production in ethanol incubation was 220.5 μM and in ethanol-xylitol incubation 32.8 μM. This was found to be mediated by inhibition of the alcohol dehydrogenase enzyme activity. Coincubation with glucose reduced the amount of produced acetaldehyde by 23% and coincubation with fructose by 29%. At concentrations that are representative of those found in the oral cavity during the intake of proprietary xylitol products, xylitol was found to reduce the production of carcinogenic acetaldehyde from ethanol by Candida below the mutagenic level of 40-100 μM.

Alcohol dehydrogenase 1 of barley modulates susceptibility to the parasitic fungus Blumeria graminis f.sp. hordei

Plant primary energy metabolism is profoundly reorganized under biotic stress conditions and there is increasing evidence for a role for the fermentative pathway in biotic interactions. However, the mechanisms regulating metabolic reprogramming are not well understood despite its critical function in the biotic stress response. Here the function of alcohol dehydrogenase (ADH) in the interaction of barley with the parasitic fungus Blumeria graminis f.sp. hordei (Bgh) is addressed. Challenge of susceptible barley leaves with Bgh resulted in transcriptional activation of HvADH1 and an induction of ADH enzyme activity starting 24 h after infection and reaching a clear-cut effect 4 d after infection. This increase in ADH enzyme activity was not observed in the resistant near-isogenic mlo5 line. Moreover, an induction of ADH enzyme activity by Bgh was enhanced in the presence of sucrose in hydroponically grown seedlings. Transient knock-down or overexpression of HvADH1 in barley epidermal cells mediated a decrease or increase in the penetration success of Bgh, respectively. Inhibition of ADH activity by pyrazole resulted in a delay in symptoms. The pyrazole effect could be overcome by adding glucose to the incubation medium, pinpointing a nutritional effect of ADH in the barley–Bgh interaction. Taken together, misexpression of pathogen-inducible HvADH1 or variation of ADH activity modulates the pathogen response of barley to the biotrophic fungal parasite Bgh. In this way, ADH knock-down/inhibition results in reduced fungal success. The possibility is discussed that ADH activity supports biotrophy by maintaining glycolytic metabolism in pathogen-stressed barley.