Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.1.1.1 (alcohol dehydrogenase)
9,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The physiology of Saccharomyces cerevisiae CBS 8066 was studied in glucose-limited chemostat cultures. Below a dilution rate of 0.30 h-1 glucose was completely respired, and biomass and CO2 were the only products formed. Above this dilution rate acetate and pyruvate appeared in the culture fluid, accompanied by disproportional increases in the rates of oxygen consumption and carbon dioxide production. This enhanced respiratory activity was accompanied by a drop in cell yield from 0.50 to 0.47 g (dry weight) g of glucose-1. At a dilution rate of 0.38 h-1 the culture reached its maximal oxidation capacity of 12 mmol of O2 g (dry weight)-1 h-1. A further increase in the dilution rate resulted in aerobic alcoholic fermentation in addition to respiration, accompanied by an additional decrease in cell yield from 0.47 to 0.16 g (dry weight) g of glucose-1. Since the high respiratory activity of the yeast at intermediary dilution rates would allow for full respiratory metabolism of glucose up to dilution rates close to mumax, we conclude that the occurrence of alcoholic fermentation is not primarily due to a limited respiratory capacity. Rather, organic acids produced by the organism may have an uncoupling effect on its respiration. As a result the respiratory activity is enhanced and reaches its maximum at a dilution rate of 0.38 h-1. An attempt was made to interpret the dilution rate-dependent formation of ethanol and acetate in glucose-limited chemostat cultures of S. cerevisiae CBS 8066 as an effect of overflow metabolism at the pyruvate level. Therefore, the activities of pyruvate decarboxylase, NAD+- and NADP+-dependent acetaldehyde dehydrogenases, acetyl coenzyme A (acetyl-CoA) synthetase, and alcohol dehydrogenase were determined in extracts of cells grown at various dilution rates. From the enzyme profiles, substrate affinities, and calculated intracellular pyruvate concentrations, the following conclusions were drawn with respect to product formation of cells growing under glucose limitation. (i) Pyruvate decarboxylase, the key enzyme of alcoholic fermentation, probably already is operative under conditions in which alcoholic fermentation is absent. The acetaldehyde produced by the enzyme is then oxidized via acetaldehyde dehydrogenases and acetyl-CoA synthetase. The acetyl-CoA thus formed is further oxidized in the mitochondria. (ii) Acetate formation results from insufficient activity of acetyl-CoA synthetase, required for the complete oxidation of acetate. Ethanol formation results from insufficient activity of acetaldehyde dehydrogenases.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Enzymic analysis of the crabtree effect in glucose-limited chemostat cultures of Saccharomyces cerevisiae. 256 99

Growth and metabolite formation were studied in oxygen-limited chemostat cultures of Saccharomyces cerevisiae CBS 8066 and Candida utilis CBS 621 growing on glucose or maltose at a dilution rate of 0.1 h-1. With either glucose or maltose S. cerevisiae could be grown under dual limitation of oxygen and sugar. Respiration and alcoholic fermentation occurred simultaneously and the catabolite fluxes through these processes were dependent on the magnitude of the oxygen feed. C. utilis could also be grown under dual limitation of glucose and oxygen. However, at very low oxygen feed rates (i.e. below 4 mmol l-1 h-1) growth was limited by oxygen only, as indicated by the high residual glucose concentration in the culture. In contrast to S. cerevisiae, C. utilis could not be grown anaerobically at a dilution rate of 0.1 h-1. With C. utilis absence of oxygen resulted in wash-out, despite the presence of ergosterol and Tween-80 in the growth medium. The behaviour of C. utilis with respect to maltose utilization in oxygen-limited cultures was remarkable: alcoholic fermentation did not occur and the amount of maltose metabolized was dependent on the oxygen supply. Oxygen-limited cultures of C. utilis growing on maltose always contained high residual sugar concentrations. These observations throw new light on the so-called Kluyver effect. Apparently, maltose is a non-fermentable sugar for C. utilis CBS 621, despite the fact that it can serve as a substrate for growth of this facultatively fermentative yeast. This is not due to the absence of key enzymes of alcoholic fermentation. Pyruvate decarboxylase and alcohol dehydrogenase were present at high levels in maltose-utilizing cells of C. utilis grown under oxygen limitation. It is concluded that the Kluyver effect, in C. utilis growing on maltose, results from a regulatory mechanism that prevents the sugar from being fermented. Oxygen is not a key factor in this phenomenon since under oxygen limitation alcoholic fermentation of maltose was not triggered.
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PMID:Effects of oxygen limitation on sugar metabolism in yeasts: a continuous-culture study of the Kluyver effect. 801 92

Two genes coding for isozymes of alcohol dehydrogenase (ADH); designated PsADH1 and PsADH2, have been identified and isolated from Pichia stipitis CBS 6054 genomic DNA by Southern hybridization to Saccharomyces cerevisiae ADH genes, and their physiological roles have been characterized through disruption. The amino acid sequences of the PsADH1 and PsADH2 isozymes are 80.5% identical to one another and are 71.9 and 74.7% identical to the S. cerevisiae ADH1 protein. They also show a high level identity with the group I ADH proteins from Kluyveromyces lactis. The PsADH isozymes are presumably localized in the cytoplasm, as they do not possess the amino-terminal extension of mitochondrion-targeted ADHs. Gene disruption studies suggest that PsADH1 plays a major role in xylose fermentation because PsADH1 disruption results in a lower growth rate and profoundly greater accumulation of xylitol. Disruption of PsADH2 does not significantly affect ethanol production or aerobic growth on ethanol as long as PsADH1 is present. The PsADH1 and PsADH2 isozymes appear to be equivalent in the ability to convert ethanol to acetaldehyde, and either is sufficient to allow cell growth on ethanol. However, disruption of both genes blocks growth on ethanol. P. stipitis strains disrupted in either PsADH1 or PsADH2 still accumulate ethanol, although in different amounts, when grown on xylose under oxygen-limited conditions. The PsADH double disruptant, which is unable to grow on ethanol, still produces ethanol from xylose at about 13% of the rate seen in the parental strain. Thus, deletion of both PsADH1 and PsADH2 blocks ethanol respiration but not production, implying a separate path for fermentation.
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PMID:Pichia stipitis genes for alcohol dehydrogenase with fermentative and respiratory functions. 954 72

Kluyveromyces lactis is an important industrial yeast, as well as a popular laboratory model. There is currently no consensus in the literature on the physiology of this yeast, in particular with respect to aerobic alcoholic fermentation ('Crabtree effect'). This study deals with regulation of alcoholic fermentation in K. lactis CBS 2359, a proposed reference strain for molecular studies. In aerobic, glucose-limited chemostate cultures (D = 0.05-0.40 h-1) growth was entirely respiratory, without significant accumulation of ethanol or other metabolities. Alcoholic fermentation occurred in glucose-grown shake-flask cultures, but was absent during batch cultivation on glucose in fermenters under strictly aerobic conditions. This indicated that ethanol formation in the shake-flask cultures resulted from oxygen limitation. Indeed, when the oxygen feed to steady-state chemostat cultures (D = 0.10 h-1) was lowered, a mixed respirofermentative metabolism only occurred at very low dissolved oxygen concentrations (less than 1% of air saturation). The onset of respirofermentative metabolism as a result of oxygen limitation was accompanied by an increase of the levels of pyruvate decarboxylase and alcohol dehydrogenase. When aerobic, glucose-limited chemostat cultures (D = 0.10 h-1) were pulsed with excess glucose, ethanol production did not occur during the first 40 min after the pulse. However, a slow aerobic ethanol formation was invariably observed after this period. Since alcoholic fermentation did not occur in aerobic batch cultures this is probably a transient response, caused by an imbalanced adjustment of enzyme levels during the transition from steady-state growth at mu = 0.10 h to growth at mu max. It is concluded that in K. lactis, as in other Crabtree-negative yeasts, the primary environmental trigger for occurrence of alcoholic fermentation is oxygen limitation.
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PMID:Regulation of alcoholic fermentation in batch and chemostat cultures of Kluyveromyces lactis CBS 2359. 955 53

Regulation of currently identified genes involved in pyruvate metabolism of Kluyveromyces lactis strain CBS 2359 was studied in glucose-limited, ethanol-limited and acetate-limited chemostat cultures and during a glucose pulse added to a glucose-limited steady-state culture. Enzyme activity levels of the pyruvate dehydrogenase complex, pyruvate decarboxylase, alcohol dehydrogenase, acetyl-CoA synthetase and glucose-6-phosphate dehydrogenase were determined in all steady-state cultures. In addition, the mRNA levels of KlADH1-4, KlACS1, KlACS2, KlPDA1, KlPDC1 and RAG1 were monitored under steady-state conditions and during glucose pulses. In K. lactis, as in Saccharomyces cerevisiae, enzymes involved in glucose utilization (glucose-6-phosphate dehydrogenase, pyruvate dehydrogenase, pyruvate decarboxylase) showed the highest expression levels on glucose, whereas enzymes required for ethanol or acetate consumption (alcohol dehydrogenase, acetyl-CoA synthetase) showed the highest enzyme activities on ethanol. In cases where mRNA levels were determined, these corresponded well with the corresponding enzyme activities, suggesting that regulation is mostly achieved at the transcriptional level. Surprisingly, the activity of the K. lactis pyruvate dehydrogenase complex appeared to be regulated at the level of KlPDA1 transcription. The conclusions from the steady-state cultures were corroborated by glucose pulse experiments. Overall, expression of the enzymes of pyruvate metabolism in the Crabtree-negative yeast K. lactis appeared to be regulated in the same way as in Crabtree-positive S. cerevisiae, with one notable exception: the PDA1 gene encoding the E1alpha subunit of the pyruvate dehydrogenase complex is expressed constitutively in S. cerevisiae.
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PMID:Regulation of pyruvate metabolism in chemostat cultures of Kluyveromyces lactis CBS 2359. 1080 23

The effects of ethanol and 1-octanol on growth and fatty acid composition of different strains of Kluyveromyces lactis containing a mutation in the four different alcohol dehydrogenase (KlADH) genes were investigated. In the presence of ethanol and 1-octanol K. lactis reduced the fluidity of its lipids by decreasing the unsaturation index (UI) of its membrane fatty acids. In this way, a direct correlation between nonlethal ethanol concentrations and the decrease in the UI could be observed. At concentrations which totally inhibited cell growth no reaction occurred. These adaptive modifications of the fatty acid pattern of K. lactis to ethanol contrasted with those reported for Saccharomyces cerevisiae and Schizosaccharomyces pombe. Whereas these two yeasts increased the fluidity of their membrane lipids in the presence of ethanol, K. lactis reduced the fluidity (UI) of its lipids. Among the different isogenic adh negative strains tested, the strain containing no ADH (adh0) and that containing only KlADH1 were the most alcohol-sensitive. The strain with only KlADH2 showed nearly the same tolerance as reference strain CBS 2359/152 containing all four ADH genes. This suggests that the KlADH2 product could play an important role in the adaptation/detoxification reactions of K. lactis to high ethanol concentrations.
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PMID:Ethanol tolerance and membrane fatty acid adaptation in adh multiple and null mutants of Kluyveromyces lactis. 1113 Aug 68

Null mutations in the structural gene encoding phosphoglucose isomerase completely abolish activity of this glycolytic enzyme in Kluyveromyces lactis and Saccharomyces cerevisiae. In S. cerevisiae, the pgi1 null mutation abolishes growth on glucose, whereas K.lactis rag2 null mutants still grow on glucose. It has been proposed that, in the latter case, growth on glucose is made possible by an ability of K. lactis mitochondria to oxidize cytosolic NADPH. This would allow for a re-routing of glucose dissimilation via the pentose-phosphate pathway. Consistent with this hypothesis, mitochondria of S. cerevisiae cannot oxidize NADPH. In the present study, the ability of K. lactis mitochondria to oxidize cytosolic NADPH was experimentally investigated. Respiration-competent mitochondria were isolated from aerobic, glucose-limited chemostat cultures of the wild-type K. lactis strain CBS 2359 and from an isogenic rag2Delta strain. Oxygen-uptake experiments confirmed the presence of a mitochondrial NADPH dehydrogenase in K.lactis. This activity was ca. 2.5-fold higher in the rag2Delta mutant than in the wild-type strain. In contrast to mitochondria from wild-type K. lactis, mitochondria from the rag2Delta mutant exhibited high rates of ethanol-dependent oxygen uptake. Subcellular fractionation studies demonstrated that, in the rag2Delta mutant, a mitochondrial alcohol dehydrogenase was present and that activity of a cytosolic NADPH-dependent 'acetaldehyde reductase' was also increased. These observations indicate that two mechanisms may participate in mitochondrial oxidation of cytosolic NADPH by K. lactis mitochondria: (a) direct oxidation of cytosolic NADPH by a mitochondrial NADPH dehydrogenase; and (b) a two-compartment transhydrogenase cycle involving NADP(+)- and NAD(+)-dependent alcohol dehydrogenases.
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PMID:Two mechanisms for oxidation of cytosolic NADPH by Kluyveromyces lactis mitochondria. 1211 36

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