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PubMed2006

Abnormal transsulfuration and glutathione metabolism in the micropig model of alcoholic liver disease.

BACKGROUND: Alcoholic liver disease is associated with abnormalities of methionine metabolic enzymes that may contribute to glutathione depletion. Previously, we found that feeding micropigs a combination of ethanol with a folate-deficient diet resulted in the greatest decreases in S-adenosylmethionine and glutathione and increases in liver S-adenosylhomocysteine and oxidized disulfide glutathione. METHODS: To study the mechanisms of glutathione depletion, we analyzed the transcripts and activities of enzymes involved in its synthesis and metabolism in liver and plasma specimens that were available from the same micropigs that receive folate-sufficient or folate-depleted diets with or without 40% of energy as ethanol for 14 weeks. RESULTS: Ethanol feeding, folate deficiency, or their combination decreased liver and plasma glutathione and the activities of hepatic copper-zinc superoxide dismutase and glutathione peroxidase and increased the activity of manganese superoxide dismutase and glutathione reductase. Hepatic levels of cysteine and taurine were unchanged while plasma cysteine was increased in the combined diet group. Cystathionine beta-synthase transcripts and activity were unaffected by ethanol feeding, while the activities of other transsulfuration enzymes involved in glutathione synthesis were increased. Glutathione transferase transcripts were increased 4-fold and its mean activity was increased by 34% in the combined ethanol and folate-deficient diet group, similar in magnitude to the observed 36% reduction in hepatic glutathione. CONCLUSIONS: Chronic ethanol feeding and folate deficiency acted individually or synergistically to affect methionine metabolism in the micropig by depleting glutathione pools and altering transcript expressions and activities of enzymes involved in its synthesis, utilization, and regeneration. The data suggest that the observed decrease in hepatic glutathione during ethanol feeding reflects its increased utilization to meet increased antioxidant demands, rather than reduction in its synthesis.

Animals↗
PubMed1996

Xylulose and glucose fermentation by Saccharomyces cerevisiae in chemostat culture.

Saccharomyces cerevisiae ATCC 24860 was cultivated in chemostat culture under anoxic conditions with 111.1 mmol of glucose liter-1 alone or with a mixture of 66.7 mmol of xylulose liter-1 and 111.1 mmol of glucose liter-1. The substrate consumption rate was 5.4 mmol g of cells-1 h-1 for glucose, whereas for xylulose it was 1.0 mmol g of cells-1 h-1. The ethanol yield decreased from 0.52 carbon mole of ethanol produced per carbon mole of sugar consumed during the utilization of glucose alone to 0.49 carbon mole produced per carbon mole consumed during the simultaneous utilization of xylulose and glucose, while cell biomass was maintained at 2.04 to 2.10 g liter-1. Xylulose coutilization was accompanied by a shift in product formation from ethanol to acetate and arabinitol. Xylulokinase activity was absent during glucose metabolism but detectable during simultaneous utilization of xylulose and glucose. Xylulose cometabolism resulted in increased in vitro activity of pyruvate decarboxylase and an increased concentration of the intracellular metabolite fructose 1,6-diphosphate without significant changes in the concentrations of 6-phosphogluconate and pyruvate. The results are discussed in relation to (i) altered enzyme activities and (ii) the redox flux of the cell.

Glucose↗
PubMed1979

Dose-related effects of ethanol on avoidance-avoidance conflict behavior in the rat.

The effects of ethanol on avoidance-avoidance conflict behavior were examined, utilizing a 3- x -3 factorial design in which rats were trained and tested after drinking sugar-water solutions containing 0, 3, or 6% ethanol. Avoidance tendencies were established by initially training rats to escape from electric shock by running in one direction in a white alley, and in the opposite direction in a black alley. In subsequent shock free conflict tests, the rats were placed into an alley with one black wall and one white wall, an environment in which incompatible tendencies to avoid both ends of the alley were aroused. During training, ethanol decreased the speeds with which rats escaped shock. In the subsequent avoidance-avoidance conflict tests, rats that previously received shock escape training after drinking ethanol ran more slowly, and exhibited lower total movement and oscillation range scores than did animals trained after drinking plain sugar-water. Administration of ethanol just prior to the conflict tests resulted in dose-related increases in running speeds, total movement scores, and oscillation ranges. These results suggest that moderate doses of ethanol increased responding by differentially weakening conflicting avoidance tendencies.

Alcohol Drinking↗
PubMed1985

The effect of temperature and chronic ethanol feeding on the proton electrochemical potential and phosphate potential in rat liver mitochondria.

The relationship between the proton electrochemical potential (delta mu H) and the maximal free energy of ATP hydrolysis (delta GP) in coupled respiring rat liver mitochondria was investigated as a function of temperature and chronic ethanol-feeding. The flow dialysis method was utilized to measure the temperature dependence of delta mu H from the uptake of 86Rb (in the presence of valinomycin) and [14C]DMO. delta GP in state 4 was determined by a null-point titration of the reversible, H+-coupled ATPase against the phosphate potential. delta mu H increases with temperature from 196 mV at 10 degrees C, to 217 mV at 40 degrees C. The maximal delta GP at state 4 decreases as a function of temperature from 67.8 kJ/mol at 10 degrees C, to 54.8 kJ/mol at 40 degrees C. As a result, the ratio delta GP/delta mu H decreases with temperature from 3.56 at 10 degrees C to 2.60 at 40 degrees C. Similar studies with mitochondria from rats which were chronically fed with ethanol show that, while delta GP at state 4 decreases in these rats from 61.2 to 56.0 (25 degrees C), the delta mu H is essentially unchanged at 212 mV. Thus the ratio delta GP/delta mu H in ethanol-fed rats at 25 degrees C is 2.77 as compared with 2.97 in control. Similar reduction of delta GP was observed in inverted inner membranes from ethanol-fed rats. Both the temperature dependence of delta GP/delta mu H and the effect of ethanol-feeding cannot be easily explained by the chemiosmotic hypothesis which postulates that delta mu H is the only driving force for ATP synthesis. In contrast, a parallel coupling model, which postulates that intramembrane proton transfer from redox pumps to ATPase is mediated by the formation of dynamic aggregates of the mitochondrial inner-membrane proteins, can easily accommodate these findings. Accordingly, the temperature effect is due to weakening of these fragile aggregates, while the ethanol-feeding effect is the result of reduced concentration of active pumps, which decrease the frequency of formation of functional aggregates.

Adenosine Triphosphate↗
PubMed2004

Inhibition of ethanol-producing yeast and bacteria by degradation products produced during pre-treatment of biomass.

An overview of the different inhibitors formed by pre-treatment of lignocellulosic materials and their inhibition of ethanol production in yeast and bacteria is given. Different high temperature physical pre-treatment methods are available to render the carbohydrates in lignocellulose accessible for ethanol fermentation. The resulting hydrolyzsates contain substances inhibitory to fermentation-depending on both the raw material (biomass) and the pre-treatment applied. An overview of the inhibitory effect on ethanol production by yeast and bacteria is presented. Apart from furans formed by sugar degradation, phenol monomers from lignin degradation are important co-factors in hydrolysate inhibition, and inhibitory effects of these aromatic compounds on different ethanol producing microorganisms is reviewed. The furans and phenols generally inhibited growth and ethanol production rate (Q(EtOH)) but not the ethanol yields (Y(EtOH)) in Saccharomyces cerevisiae. Within the same phenol functional group (aldehyde, ketone, and acid) the inhibition of volumetric ethanol productivity was found to depend on the amount of methoxyl substituents and hence hydrophobicity (log P). Many pentose-utilizing strains Escherichia coli, Pichia stipititis, and Zymomonas mobilis produce ethanol in concentrated hemicellulose liquors but detoxification by overliming is needed. Thermoanaerobacter mathranii A3M3 can grow on pentoses and produce ethanol in hydrolysate without any need for detoxification.

Bacteria↗
PubMed1961

Endogenous respiration of Bacillus cereus.

Clifton, C. E. (Stanford University, Stanford, Calif.), and J. M. Sobek. Endogenous respiration of Bacillus cereus. J. Bacteriol. 82:252-256. 1961.-The endogenous respiration of washed cells of Bacillus cereus varies with the nature of the growth medium and with time. The respiratory quotient of cells harvested from nutrient agar remained quite constant around 1.00 over a 2-hr period of respiration, whereas that of cells grown on glucose-nutrient agar decreased from 0.97 for the first hour to 0.87 for the second hour. Considerable amounts of ammonia were formed, the number of moles per mole of oxygen consumed decreasing with time for agar-grown cells and increasing for glucose-grown ones.C(14)-labeled, agar-grown cells utilized materials insoluble in cold or hot 5% trichloroacetic acid, ethanol, or chloroform as their endogenous substrate, the same behavior being noted with glucose-grown cells except that they utilized both hot trichloroacetic-soluble and -insoluble materials. These results indicate that the bulk of the endogenous substrates are chemically complex and, at least in part, are nitrogenous in character.

Agar↗
PubMed1981

Effects of acute ethanol exposure upon in vivo leucine uptake and protein synthesis in the fetal rat.

Tritiated L-leucine ((3H)L-leu) was injected into the amniotic sacs of 19-day gestation rat fetuses during a brief (4-hr) period of elevation in maternal serum ethanol. The pregnant rats received 47.5% ethanol at "high dose" (0.29 to 0.33 g/100 g body weight) or "low dose" (0.12 to 0.14 g/100 gm body weight) by intraperitoneal injection. Fetal brain and liver were removed and analyzed for tissue uptake (TU) and protein incorporation (PI) of (3H)L-leu. Relative protein synthesis, independent of alterations in TU, was expressed by the ratio PI/TU x 100. Delayed fetal effects of acute maternal ethanol exposure were studied by injecting the fetal amniotic sacs with (3H)L-leu 24 hr after maternal ethanol administration. Both TU and PI were decreased in high dose fetal brain. Liver PI, but not TU, was depressed. High dose ethanol treatment caused a reduction in protein synthesis (PI/TU x 100) in fetal brain but not liver. Low dose ethanol enhanced brain PI and both liver and brain PI/TU x 100. Utilization of (3H)L-leu was related to fourth-hour (sacrifice) maternal serum ethanol levels. Fetal brain was more strikingly affected than liver. Ethanol concentrations greater than 200 mg/dl caused a decrease in brain TU (control, 1879 +/- 185 versus ethanol, 1219 +/- 123 dpm/mg protein) and PI/TU x 100 (control, 48.9 +/- 3.3 versus ethanol, 31.5 +/- 2.9). At levels less than 100 mg/dl, PI/TU x 100 was enhanced in both brain (control, 48.9 +/- 3.3 versus ethanol, 67.3 +/- 2.8) and liver (control, 45.3 +/- 4.2 versus ethanol, 62.3 +/- 1.7). Tissue uptake of (3H)L-leu 24 hr after high dose maternal ethanol exposure was increased in fetal brain. The results support the hypothesis that a brief period of maternal/fetal ethanol exposure, similar to that found in "social" drinking humans, alters normal fetal metabolism.

Animals↗
PubMed2000

Ethanol production from glucose and xylose by immobilized Zymomonas mobilis CP4(pZB5).

Fermentation of glucose-xylose mixtures to ethanol was investigated in batch and continuous experiments using immobilized recombinant Zymomonas mobilis CP4(pZB5). This microorganism was immobilized by entrapment in kappa-carrageenan beads having a diameter of 1.5-2.5 mm. Batch experiments showed that the immobilized cells cofermented glucose and xylose to ethanol and that the presence of glucose improved the xylose utilization rate. Batch fermentation of rice straw hydrolysate containing 76 g/L of glucose and 33.8 g/L of xylose gave an ethanol concentration of 44.3 g/L after 24 h, corresponding to a yield of 0.46 g of ethanol/g of sugars. Comparable results were achieved with a synthetic sugar control. Continuous fermentation experiments were performed in a laboratory-scale fluidized-bed bioreactor (FBR). Glucose-xylose feed mixtures were pumped through the FBR at residence times of 2-4 h. Glucose conversion to ethanol was maintained above 98% in all experiments. Xylose conversion to ethanol was highest at 91.5% for a feed containing 50 g/L of glucose and 13 g/L of xylose at a dilution rate of 0.24/h. The xylose conversion to ethanol decreased with increasing feed xylose concentration, dilution rate, and age of the immobilized cells. Volumetric ethanol productivities in the range of 6.5-15.3 g/L.h were obtained. The improved productivities achieved in the FBR compared to other bioreactor systems can help in reducing the production costs of fuel ethanol from lignocellulosic sugars.

Aldose-Ketose Isomerases↗
PubMed2006

Degradation of ethanol plant by-products by Exophiala lecanii-corni and Saccharomyces cerevisiae in batch studies.

By-product emissions from ethanol production facilities have become a public health concern. Many of these by-products are classified as hazardous air pollutants by the USEPA and current treatment methods, mainly thermal-oxidation, for these compounds are costly, energy intensive, and may produce other undesirable by-products. Degradation of these by-products by the fungi Exophiala lecanii-corni and Saccharomyces cerevisiae was explored. Ethanol plant by-products, focused on in this study, included formaldehyde, acetaldehyde, ethanol, methanol, glycerol, acetic acid, and lactic acid. Initial batch studies were conducted to determine degradation rates and whether the contaminants would be toxic to the fungi. These batch studies demonstrated that E. lecanii-corni and S. cerevisiae are able to utilize all but methanol and formaldehyde as sole carbon and energy sources for growth; however, both contaminants were utilized as secondary metabolites by cultures initially fed either ethanol or acetic acid. Growth studies also were conducted using two contaminants simultaneously to determine if the presence of one contaminant inhibited the degradation of another. Growth and contaminant utilization was observed in cultures fed two contaminants simultaneously.

Acetaldehyde↗
PubMed1998

Note: sucrose transport and metabolism in Clostridium beijerinckii NCIMB 8052.

Sucrose is the major carbon source in molasses, the traditional substrate employed in the industrial acetonebutanol-ethanol (ABE) fermentation by solventogenic clostridia. The utilization of sucrose by Clostridium beijerinckii NCIMB 8052 was investigated. Extracts prepared from cultures grown on sucrose (but not xylose or fructose) as the sole carbon source possessed sucrose phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) activity. Extract fractionation and reconstitution experiments revealed that the entire sucrose Enzyme II complex resides within the membrane in this organism. Sucrose-6-phosphate hydrolase and fructokinase activities were also detected in sucrose grown cultures. The fructokinase activity, which is required specifically during growth on sucrose, was shown to be inducible under these conditions. A pathway for sucrose metabolism in this organism is proposed.

Acetone↗
PubMedDate not supplied

Clinical utility of chromosome 17 alpha satellite probe in distinguishing benign mesothelium from malignant cells: a pilot study using routinely fixed specimens.

Fluorescent in situ hybridization has shown promise in detecting malignant cells in body cavity effusions. However, this requires special preparatory techniques not used in many laboratories. We developed an in situ hybridization (ISH) procedure specifically for ethanol-fixed specimens, and using it tested the clinical utility of the chromosome 17alpha satellite probe (C17alpha). ISH with C17alpha was used in 12 malignant and 10 benign ethanol-fixed body cavity effusions. Cells were pretreated with protease K prior to ISH. The probe was detected by an anti-digoxigenin-horseradish peroxidase method. Signals were counted in 100 nuclei and the chromosome index (CI) and percent diploid cells calculated in each case. ISH was successfully performed in all cases. Malignant cells had an average CI of 2.23 with less than 44% diploid nuclei and 50% of specimens exhibited bizarre signals. Benign effusions had an average CI of 1.98 with over 84.6% diploid nuclei. Questionably bizarre signals were seen in two (20%) benign specimens. ISH can be performed on ethanol-fixed specimens. The C17alpha probe may prove valuable in detecting malignant cells in body cavity effusions.

Chromosomes, Human, Pair 17↗
PubMed2001

Response of some scolytids and their predators to ethanol and 4-allylanisole in pine forests of central Oregon.

Lindgren multiple funnel traps were set up in pine forests of central Oregon to determine the response of scolytid bark beetles to ethanol and 4-allylanisole (4AA). Traps were baited with two release rates of ethanol (4.5 or 41.4 mg/hr) and three release rates of 4AA (0, 0.6, or 4.3 mg/hr) in a 2 x 3 factorial design. All traps also released a 1:1 mixture of alpha- and beta-pinene at 11.4 mg/hr. Of 13,396 scolytids caught, Dendroctonus valens made up 60%, Hylurgops spp. 18.5%, Ips spp. 16%, Hylastes spp. 1.8%, Ganthotrichus retusus 0.9%, and bark beetle predators another 2.8%. Increasing the release rate of ethanol in the absence of 4AA increased the number of most scolytid species caught by 1.5-3.7 times, confirming its role as an attractant. Ips latidens, Temnochila chlorodia, and clerid predators were exceptions and did not show a response to higher ethanol release rates. Release of 4AA at the lowest rate inhibited attraction of most scolytids, with a significant reduction in G. retusus, Hylastes macer, and Hylurgops porosus when compared to traps without 4AA. A high release rate of 4AA further inhibited responses for most beetles compared to low 4AA. Seven species were significantly deterred by high 4AA, including the latter three, and Hylastes longicollis, Hylastes nigrinus, Hylurgops reticulatus, and Ips latidens. Exceptions include Hylurgops subcostulatus, which was significantly attracted to both low and high 4AA, and I. pini, which was attracted to low and high 4AA in combination with low ethanol, but unaffected by either release of 4AA with high ethanol. Dendroctonus valens was significantly attracted to low 4AA and unaffected by high 4AA. Predators appeared to be less inhibited by 4AA than most bark beetles. Although 4AA can deter the attraction of some secondary bark beetles to ethanol in combination with alpha- and beta-pinene, this inhibition could be weakened for certain species by increasing ethanol release rates. 4-Allylanisole may have some utility for managing the behavior of secondary bark beetles sensitive to this compound.

Animals↗
PubMed2002

Emissions of aldehydes and ketones from a two-stroke engine using ethanol and ethanol-blended gasoline as fuel.

Besides aliphatic gasoline, ethanol-blended gasoline intended for use in small utility engines was recently introduced on the Swedish market. For small utility engines, little data is available showing the effects of these fuels on exhaust emissions, especially concerning aldehydes and ketones (carbonyls). The objective of the present investigation was to study carbonyl emissions and regulated emissions from a two-stroke chain saw engine using ethanol, gasoline, and ethanol-blended gasoline as fuel (0%, 15%, 50%, 85%, and 100% ethanol). The effects of the ethanol-blending level and mechanical changes of the relative air/fuel ratio, lambda, on exhaust emissions was investigated, both for aliphatic and regular gasoline. Formaldehyde, acetaldehyde, and aromatic aldehydes were the most abundant carbonyls in the exhaust. Acetaldehyde dominated for all ethanol-blended fuels (1.2-12 g/kWh, depending on the fuel and lambda), and formaldehyde dominated for gasoline (0.74-2.3 g/kWh, depending on the type of gasoline and lambda). The main effects of ethanol blending were increased acetaldehyde emissions (30-44 times for pure ethanol), reduced emissions of all other carbonyls exceptformaldehyde and acrolein (which showed a more complex relation to the ethanol content), reduced carbon monoxide (CO) and ntirogen oxide (NO) emissions, and increased hydrocarbon (HC) and nitrogen dixodie (NO2) emissions. The main effects of increasing lambda were increased emissions of carbonyls and nitrogen oxides (NOx) and reduced CO and HC emissions. When the two types of gasoline are considered, benzaldehyde and tolualdehyde could be directly related to the gasoline content of aromatics or olefins, but also acrolein, propanal, crotonaldehyde, and methyl ethyl ketone mainly originated from aromatics or olefins, while the main source for formaldehyde, acetaldehyde, acetone, methacrolein, and butanal was saturated aliphatic hydrocarbons.

Air Pollutants↗
PubMed1998

Improving fermentation performance of recombinant Zymomonas in acetic acid-containing media.

In the production of ethanol from lignocellulosic biomass, the hydrolysis of the acetylated pentosans in hemicellulose during pretreatment produces acetic acid in the prehydrolysate. The National Renewable Energy Laboratory (NREL) is currently investigating a simultaneous saccharification and cofermentation (SSCF) process that uses a proprietary metabolically engineered strain of Zymomonas mobilis that can coferment glucose and xylose. Acetic acid toxicity represents a major limitation to bioconversion, and cost-effective means of reducing the inhibitory effects of acetic acid represent an opportunity for significant increased productivity and reduced cost of producing fermentation fuel ethanol from biomass. In this study, the fermentation performance of recombinant Z. mobilis 39676:pZB4L, using a synthetic hardwood prehydrolysate containing 1% (w/v) yeast extract, 0.2% KH2PO4, 4% (w/v) xylose, and 0.8% (w/v) glucose, with varying amounts of acetic acid was examine. To minimize the concentration of the inhibitory undissociated form of acetic acid, the pH was controlled at 6.0. The final cell mass concentration decreased linearly with increasing level of acetic acid over the range 0-0.75% (w/v), with a 50% reduction at about 0.5% (w/v) acetic acid. The conversion efficiency was relatively unaffected, decreasing from 98 to 92%. In the absence of acetic acid, batch fermentations were complete at 24 h. In a batch fermentation with 0.75% (w/v) acetic acid, about two-thirds of the xylose was not metabolized after 48 h. In batch fermentations with 0.75% (w/v) acetic acid, increasing the initial glucose concentration did not have an enhancing effect on the rate of xylose fermentation. However, nearly complete xylose fermentation was achieved in 48h when the bioreactor was fed glucose. In the fed-batch system, the rate of glucose feeding (0.5 g/h) was designed to simulate the rate of cellulolytic digestion that had been observed in a modeled SSCF process with recombinant Zymomonas. In the absence of acetic acid, this rate of glucose feeding did not inhibit xylose utilization. It is concluded that the inhibitory effect of acetic acid on xylose utilization in the SSCF biomass-to-ethanol process will be partially ameliorated because of the simultaneous saccharification of the cellulose.

Acetic Acid↗
PubMed2006

Near-infrared spectroscopic monitoring of biomass, glucose, ethanol and protein content in a high cell density baker's yeast fed-batch bioprocess.

The use of at-line NIRS to monitor a high cell density fed-batch baker's yeast bioprocess was investigated. Quantification of the key analytes (biomass, ethanol and glucose) and the product quality indicator (percentage protein content) was studied. Biomass was quantitatively modelled using whole matrix samples (as was percentage protein content). The dominance of the whole matrix spectrum by biomass, and its associated light scattering effects, were overcome by use of filtrate samples and adapted (semi-synthetic) filtrate samples, which allowed successful ethanol and glucose modelling, respectively. Calibrations were rigorously challenged via external validation with large sample sets relative to the calibration sample size, ensuring model robustness and potential practical utility. The standard errors of calibration for biomass, glucose, ethanol and total intracellular protein were (g/l) 1.79, 0.19, 0.79 and 0.91, respectively, comparable to those of the primary assays. The calibration strategies necessary to generate quantitative models for this range of analytes in such a complex high cell density bioprocess fluid are discussed.

Biomass↗
PubMed1989

D-xylose utilization by Saccharomyces cerevisiae.

Although it is generally accepted that Saccharomyces cerevisiae is unable to assimilate D-xylose, four strains were found to utilize xylose aerobically at different efficiencies in the presence of a mixture of substrates. The degree of D-xylose utilization by S. cerevisiae ATCC 26602 depended upon the presence of other substrates or yeast extract. The greatest amount of xylose (up to 69% over 7 d) was utilized when sugar substrates such as D-ribose were co-metabolized. Much lower degrees of utilization occurred with co-metabolism of organic acids, polyols or ethanol. A mixture of D-glucose, D-ribose, D-raffinose, glycerol and D-xylose resulted in greater xylose utilization than the presence of a single substrate and xylose. The absence of growth on a co-substrate alone did not prevent the utilization of xylose in its presence. Xylose was co-metabolized with ribose under anaerobic conditions but at a much slower rate than under aerobic conditions. When [14C]xylose was utilized in the presence of ribose under anaerobic conditions, the radioactive label was detected mainly in xylitol and not in the small amounts of ethanol produced. Under aerobic conditions the radioactive label was distributed between xylitol (91.3 +/- 0.8%), CO2 (2.6 +/- 2.3%) and biomass (1.7 +/- 0.6%). No other metabolic products were detected. Whereas most xylose was dissimilated rather than assimilated by S. cerevisiae, the organism apparently possesses a pathway which completely oxidizes xylose in the presence of another substrate.

Aerobiosis↗
PubMed1996

Acute ethanol-mediated insulin resistance in the rat: the role of ethanol oxidation.

Ethanol causes an acute and profound insulin resistance in humans and in the rat. Recent studies indicate that defects in skeletal muscle glucose uptake and utilization make a major contribution to this insulin resistance. In this study, we used the euglycaemic hyperinsulinaemic clamp to examine the role that hepatic ethanol oxidation via alcohol dehydrogenase (ADH) plays in the acute insulin resistance caused by ethanol in the rat. Treatment with the ADH inhibitor 4-methylpyrazole (4-MP) failed to abolish the insulin resistance as expressed as a decrease in the rate of glucose infusion required to maintain euglycaemia (GIR). A decrease in GIR was also observed in response to tert-butanol, an alcohol that is not a substrate for hepatic ADH. These results indicate that oxidation via ADH is not a prerequisite for the inhibition by ethanol of whole-body glucose utilization. In a separate study, we examined the relationship between blood ethanol concentration and GIR in order to determine the potency of ethanol in causing insulin resistance. These experiments showed that even at low blood concentrations (<2 mM), ethanol caused a profound decrease in GIR, similar in magnitude to that observed at higher blood concentrations (approximately 40 mM)

Journal Article↗
PubMed1997

Fermentation of biomass-derived glucuronic acid by pet expressing recombinants of E. coli B.

The economics of large-scale production of fuel ethanol from biomass and wastes requires the efficient utilization of all the sugars derived from the hydrolysis of the heteropolymeric hemicellulose component of lignocellulosic feedstocks. Glucuronic and 4-O-methyl-glucuronic acids are major side chains in xylans of the grasses and hardwoods that have been targeted as potential feedstocks for the production of cellulosic ethanol. The amount of these acids is similar to that of arabinose, which is now being viewed as another potential substrate in the production of biomass-derived ethanol. This study compared the end-product distribution associated with the fermentation of D-glucose (Glc) and D-glucuronic acid (GlcUA) (as sole carbon and energy sources) by Escherichia coli B (ATCC 11303) and two different ethanologenic recombinants--a strain in which pet expression was via a multicopy plasmid (pLOI297) and a chromosomally integrated construct, strain KO11. pH-stat batch fermentations were conducted using a modified LB medium with 2% (w/v) Glc or GlcUA with the set-point for pH control at either 6.3 or 7.0. The nontransformed host culture produced only lactic acid from glucose, but fermentation of GlcUA yielded a mixture of ethanol, acetic, and lactic acids, with acetic acid being the predominant end-product. The ethanol yield associated with GlcUA fermentation by both recombinants was similar, but acetic acid was a significant by-product. Increasing the pH from 6.3 to 7.0 increased the rate of glucuronate fermentation, but it also decreased the ethanol mass yield from 0.22 to 0.19 g/g primarily because of an increase in acetic acid production. In all fermentations there was good closure of the carbon mass balance, the exception being the recombinant bearing plasmid pLOI297 that produced an unidentified product from GlcUA. The metabolism of GlcUA by this metabolically engineered construct remains unresolved. The results offered insights into metabolic fluxes and the regulation of pyruvate catabolism in the wild-type and engineered strains. End-product distribution for metabolism of glucuronic acid by the nontransformed, wild-type E. coli B and recombinant strain KO11 suggests that the enzyme pyruvate-formate lyase is not solely responsible for the production of acetylCoA from pyruvate and that derepressed pyruvate dehydrogenase may play a significant role in the metabolism of GlcUA.

Acetyltransferases↗