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  • 1
    Electronic Resource
    Electronic Resource
    Multiple forms of xylose reductase in Pachysolen tannophilus CBS4044 (1985)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 30 (1985), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Cell-free extracts of xylose-grown Pachysolen tannophilus exhibited xylose reductase activity with both NADPH and NADH. The ratio of the NADPH- and NADH-dependent activities varied with growth conditions. Affinity chromatography of cell-free extracts resulted in a separation of two xylose reductases. One was active with both NADPH and NADH, the other was specific for NADPH. Apart from this coenzyme specificity, the two enzymes also differed in their affinities for xylose and NADPH. The role of the two enzymes in xylose metabolism is discussed in relation to attempts to use P. tannophilus for the alcoholic fermentation of wood sugars.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1985.tb01102.x
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  • 2
    Electronic Resource
    Electronic Resource
    Production of catalase-free alcohol oxidase by Hansenula polymorpha (1988)
    Springer
    Applied microbiology and biotechnology 28 (1988), S. 14-19 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Many of the potential technical applications of alcohol oxidase (MOX; EC 1.1.3.13) are limited by the presence of high activities of catalase in the enzyme preparations. In order to circumvent laborious and costly purification or inactivation procedures, the induction of MOX in a catalase-negative mutant of Hansenula polymorpha has been studied. Emphasis was laid on the induction of activities of MOX and the dissimilatory enzymes in continuous cultures grown on various mixtures of formate/glucose and formaldehyde/glucose. In continuous cultures of the catalase-negative mutant grown on these mixtures, MOX can be induced efficiently. To obtain a stable and productive process, the ratio of the substrates is of critical importance. The optimal ratios of the mixtures for the catalase-negative strain for formate/glucose and formaldehyde/glucose were 3:1 and 1–2:1, respectively. Under identical cultivation conditions the wild-type strain showed similar induction patterns for MOX and the dissimilatory enzymes formaldehyde dehydrogenase (FaDH) and formate dehydrogenase (FoDH). The MOX levels in the catalase-negative strain were approx. 50% of those in the wild-type strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00250490
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  • 3
    Electronic Resource
    Electronic Resource
    Utilization of methanol by a catalase-negative mutant of Hansenula polymorpha (1988)
    Springer
    Applied microbiology and biotechnology 28 (1988), S. 286-292 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary In methanol-utilizing yeasts, catalase is an essential enzyme for the destruction of hydrogen peroxide generated by methanol oxidase (E.C. 1.1.3.13). It was found however that a catalase-negative mutant of Hansenula polymorpha is able to consume methanol in the presence of glucose in continuous cultures. At a dilution rate of 0.1 h-1, stable continuous cultures could be obtained during growth on methanol/glucose mixtures with a molar ratio of methanol/glucose between 0 to 2.4. In these cultures methanol oxidase was induced up to a level of 40% of that obtained in the wild-type strain. The hydrogen peroxide-decomposition activity of the mutant was studied in more detail by pulsing methanol to samples of steady-state cultures. Only after the addition of excess methanol the hydrogen peroxide-decomposing system became saturated, and the cells excreted hydrogen peroxide. This was accompanied by excretion of formaldehyde and a rapid loss of viability. The presence of extracellular catalase during a methanol pulse prevented the loss of viability. The nature of the alternative hydrogen peroxide-decomposing enzyme system remains to be elucidated. Its capacity strongly depended on the cultivation conditions and pretreatment of the cells. Cells grown on formaldehyde/glucose mixtures showed a lower methanol tolerance than those grown on the methanol/glucose mixtures. Freeze-drying of cells drastically enhanced the excretion of hydrogen peroxide, probably as a result of an inactivation of the decomposing system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00250457
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  • 4
    Electronic Resource
    Electronic Resource
    Continuous measurement of ethanol production by aerobic yeast suspensions with an enzyme electrode (1984)
    Springer
    Applied microbiology and biotechnology 19 (1984), S. 181-185 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary An alcohol electrode was constructed which consisted of an oxygen probe onto which alcohol oxidase was immobilized. This enzyme electrode was used, in combination with a reference oxygen electrode, to study the short-term kinetics of alcoholic fermentation by aerobic yeast suspensions after pulsing with glucose. The results demonstrate that this device is an excellent tool in obtaining quantitative data on the short-term expression of the Crabtree effect in yeasts. Samples from aerobic glucose-limited chemostat cultures of Saccharomyces cerevisiae not producing ethanol, immediately (within 2 min) exhibited aerobic alcoholic fermentation after being pulsed with excess glucose. With chemostat-grown Candida utilis, however, ethanol production was not detectable even at high sugar concentrations. The Crabtree effect in S. cerevisiae was studied in more detail with commercial baker's yeast. Ethanol formation occurred only at initial glucose concentrations exceeding 150 mg·l-1, and the rate of alcoholic fermentation increased with increasing glucose concentrations up to 1,000 mg·l-1 glucose. Similar experiments with batch cultures of certain ‘non-fermentative’ yeasts revealed that these organisms are capable of alcoholic fermentation. Thus, even under fully aerobic conditions, Hansenula nonfermentans and Candida buffonii produced ethanol after being pulsed with glucose. In C. buffonii ethanol formation was already apparent at very low glucose concentrations (10 mg·l-1) and alcoholic fermentation even proceeded at a higher rate than in S. cerevisiae. With Rhodotorula rubra, however, the rate of ethanol formation was below the detection limit, i.e., less than 0.1 mmol·g cells-1·h-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256451
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  • 5
    Electronic Resource
    Electronic Resource
    A theoretical evaluation of growth yields of yeasts (1991)
    Springer
    Antonie van Leeuwenhoek 59 (1991), S. 49-63 
    Details
    ISSN: 1572-9699
    Keywords: yeast ; yield ; energetics ; P/O-ratio ; YATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth yields ofSaccharomyces cerevisiae andCandida utilis in carbon-limited chemostat cultures were evaluated. The yields on ethanol and acetate were much lower inS. cerevisiae, in line with earlier reports that site I phosphorylation is absent in this yeast. However, during aerobic growth on glucose both organisms had the same cell yield. This can be attributed to two factors: -S. cerevisiae had a lower protein content thanC. utilis; - uptake of glucose byC. utilis requires energy whereas inS. cerevisiae it occurs via facilitated diffusion. Theoretical calculations showed that, as a result of these two factors, the ATP requirement for biomass formation inC. utilis is 35% higher than inS. cerevisiae (theoretical YATP values of 20.8 and 28.1, respectively). The experimental YATP for anaerobic growth ofS. cerevisiae on glucose was 16 g biomass·mol ATP-1 In vivo P/O-ratios can be calculated for aerobic growth on ethanol and acetate, provided that the gap between the theoretical and experimental ATP requirements as observed for growth on glucose is taken into account. This was done in two ways: - via the assumption that the gap is independent of the growth substrate (i.e. afixed amount of ATP bridges the difference between the theoretical and experimental values). - alternatively, on the assumption that the difference is a fraction of the total ATP expenditure, that is dependent on the substrate. Calculations of P/O-ratios for growth of both yeasts on glucose, ethanol, and acetate made clear that only by assuming a fixed difference between theoretical and experimental ATP requirements, the P/O-ratios are more or less independent of the growth substrate. These P/O-ratios are approximately 30% lower than the calculated mechanistic values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582119
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  • 6
    Electronic Resource
    Electronic Resource
    Physiology of yeasts in relation to biomass yields (1991)
    Springer
    Antonie van Leeuwenhoek 60 (1991), S. 325-353 
    Details
    ISSN: 1572-9699
    Keywords: yeasts ; cell yield ; bioenergetics ; YATP ; P/O-ratio ; uncoupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The stoichiometric limit to the biomass yield (maximal assimilation of the carbon source) is determined by the amount of CO2 lost in anabolism and the amount of carbon source required for generation of NADPH. This stoichiometric limit may be reached when yeasts utilize formate as an additional energy source. Factors affecting the biomass yield on single substrates are discussed under the following headings: - Energy requirement for biomass formation (YATP). YATP depends strongly on the nature of the carbon source. - Cell composition. The macroscopic composition of the biomass, and in particular the protein content, has a considerable effect on the ATP requirement for biomass formation. Hence, determination of for instance the protein content of biomass is rolevant in studies on bioenergetics. - Transport of the carbon source. Active (i.e. energy-requiring) transport, which occurs for a number of sugars and polyols, may contribute significantly to the calculated theoretical ATP requirement for biomass formation. - P/O-ratio. The efficiency of mitochondrial energy generation has a strong effect on the cell yield. The P/O-ratio is determined to a major extent by the number of proton-translocating sites in the mitochondrial respiratory chain. - Maintenance and environmental factors. Factors such as osmotic stress, heavy metals, oxygen and carbon dioxide pressures, temperature and pH affect the yield of yeasts. Various mechanisms may be involved, often affecting the maintenance energy requirement. - Metabolites such as ethanol and weak acids. Ethanol increases the permeability of the plasma membrane, whereas weak acids can act as proton conductors. - Energy content of the growth substrate. It has often been attempted in the literature to predict the biomass yield by correlating the energy content of the carbon source (represented by the degree of reduction) to the biomass yield or the percentage assimilation of the carbon source. An analysis of biomass yields of Candida utilis on a large number of carbon sources indicates that the biomass yield is mainly determined by the biochemical pathways leading to biomass formation, rather than by the energy content of the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00430373
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  • 7
    Electronic Resource
    Electronic Resource
    Substrate-accelerated death of Saccharomyces cerevisiae CBS 8066 under maltose stress (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 6 (1990), S. 149-158 
    Details
    ISSN: 0749-503X
    Keywords: Maltose transport ; α-glucosidase ; yeast ; chemostat ; cell death ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: When Saccharomyces cerevisiae CBS 8066 was grown under maltose limitation, two enzymes specific for maltose utilization were present: a maltose carrier, and the maltose-hydrolysing α-glucosidase. The role of these two enzymes in the physiology of S. cerevisiae was investigated in a comparative study in which Candida utilis CBS 621 was used as a reference organism.Maltose pulses to a maltose-limited chemostat culture of S. cerevisiae resulted in ‘substrate-accelerated death’. This was evident from: (1) enhanced protein release from cells: (2) excretion of glucose into the medium; (3) decreased viability. These effects were specific with respect to both substrate and organism: pulses of glucose to maltose-limited cultures of S. cerevisiae did not result in cell death, neither did maltose pulses to maltose-limited cultures of C. utilis. The maltose-accelerated death of S. cerevisiae is most likely explained in terms of an uncontrolled uptake of maltose into the cell, resulting in an osmotic burst. Our results also provide evidence that the aerobic alcoholic fermentation that occurs after pulsing sugars to sugar-limited cultures of S. cerevisiae (short-term Crabtree effect) cannot solely be explained in terms of the mechanism of sugar transport. Both glucose and maltose pulses to maltose-limited cultures triggered aerobic alcohol formation. However, glucose transport by S. cerevisiae occurs via facilitated diffusion, whereas maltose entry into this yeast is mediated by a maltose/proton symport system.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320060209
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrogen peroxide as an electron acceptor for mitochondrial respiration in the yeast Hansenula polymorpha (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 7 (1991), S. 137-146 
    Details
    ISSN: 0749-503X
    Keywords: Cytochrome c peroxidase ; hydrogen peroxide ; energetics ; yeast ; anaerobic respiration ; chemostat ; mitochondria ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Chemostat cultures of a catalase-negative mutant of Hansenula polymorpha CBS 4732 were able to decompose hydrogen peroxide at a high rate. This was apparent from experiments in which yeast was grown under carbon limitation in chemostat culture on mixtures of glucose and H2O2. The enzyme responsible for H2O2 degradation is probably the mitochondrial enzyme cytochrome c peroxidase (CCP), which was present at very high activities. This enzyme was partially purified and shown to be specific for reduced cytochrome c as an electron donor; no reaction was observed with NAD(P)H. Thus, reducing equivalents for H2O2 degradation by CCP must be provided by the respiratory chain.That H2O2 can act as an electron acceptor for reducing equivalents could be confirmed with experiments in which cells were incubated with ethanol and H2O2 in the absence of oxygen. This resulted in oxidation of ethanol to equimolar amounts of acetate.Energetic aspects of mitochondrial H2O2 decomposition via CCP and the physiological function of CCP in yeasts are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320070207
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  • 9
    Electronic Resource
    Electronic Resource
    Properties of enzymes which reduce dihydroxyacetone and related compounds in hansenula polymorpha CBS 4732 (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 4 (1988), S. 117-126 
    Details
    ISSN: 0749-503X
    Keywords: Yeasts ; dihydroxyacetone ; acetoin ; diacetyl ; acetol ; methylglyoxal, acetone ; glycerol ; 1,2-propanediol ; 2,3-butanediol ; dehydrogenase ; reductase ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Hansenula polymorpha CBS 4732 grown on a variety of substrates contained very high activities of enzymes catalyzing the NADH-linked reduction of dihydroxyacetone, acetoin, diacetyl, acetol, methylglyoxal and acetone. The enzymes catalyzing these reductions have been purified and their kinetic properties are described. Three different enzymes were found responsible for the above-mentioned activities, namely: (1) dihydroxyacetone reductase; (2) acetone reductase; and (3) alcohol dehydrogenase.So far, the physiological function of dihydroxyacetone reductase and acetone reductase is obscure. The kinetic properties of dihydroxyacetone reductase and the regulation of the synthesis of this enzyme suggest that it does not function as a glycerol dehydrogenase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320040205
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  • 10
    Electronic Resource
    Electronic Resource
    Purification and properties of dihydroxyacetone reductase and 2,3-butanediol dehydrogenase from Candida utilis CBS 621 (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 4 (1988), S. 127-133 
    Details
    ISSN: 0749-503X
    Keywords: Dihydroxyacetone reductase ; 2,3-butanediol dehydrogenase ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Candida utilis CBS 621 contained four different enzymes capable of reducing carbonyl compounds such as dihydroxyacetone, acetoin, diacetyl, acetol, methylglyoxal and acetone, namely alcohol dehydrogenase, acetone reductase, dihydroxyacetone reductase and 2,3-butanediol dehydrogenase. The dihydroxyacetone reductase of C. utilis did not oxidize glycerol, thus providing evidence that this enzyme cannot function as a glycerol-2-dehydrogenase during growth of the yeast on glycerol. This enzyme may, however, play a role in the assimilation of 2,3-butanediol by C. utilis. The organism also contained a separate 2,3-butanediol dehydrogenase which was unable to reduce dihydroxyacetone. Both dihydroxyacetone reductase and 2,3-butanediol dehydrogenase were present at very high activities during growth of C. utilis on a variety of substrates, including 2,3-butanediol.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320040206
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