New mutants resistant to glucose repression affected in the regulation of the NADH reoxidation

Spontaneous mutants resistant to vanadate, arsenate or thiophosphate were isolated from a haploid strain of Saccharomyces cerevisiae. These three anions have an inhibitory effect on some mitochondrial functions and at the level of glyceraldehyde 3-phosphate dehydrogenase, a glycolysis enzyme. All the selected mutants had the same phenotype: they were deficient in alcohol dehydrogenase I, the terminal enzyme of the glycolysis, and possessed a high content of cytochrome c oxidase, the terminal enzyme of the respiratory chain. Moreover, cytochrome c oxidase biosynthesis had become insensitive to the catabolite repression, while the biosynthesis of the other enzymes sensitive to this phenomenon were always inhibited by glucose. Metabolic effects of this pleiotropic mutation manifested themselves in the following ways. 1. Growth rate and final cell mass were enhanced, compared to the wild type, when cells were grown on glucose or on glycerol, but not on lactate or ethanol. 2. Growth under anaerobiosis was nil and mutants did not ferment. 3. Mitochondrial respiration of the mutant strains was identical to the wild type with succinate or 2-oxo-glutarate as substrate, and weak with ethanol. But with added NADH, respiration rate of the mutants was higher than that of the wild type and partially insensitive to antimycin, even when cells were grown in repression conditions. It is postulated that in mutants strains, NADH produced at the level of glyceraldehyde 3-phosphate dehydrogenase, failing to be reoxidized via alcohol dehydrogenase, could be reoxidized with a high turnover owing to the enhancement of the amount of cytochrome c oxidase. Since NADH reoxidation is partially insensitive to antimycin, a secondary pathway going from external NADH dehydrogenase to cytochrome c oxidase is suggested.     

The oxidation of external NADH by an intermembrane electron transfer in mitochondria from the ubiquinone-deficient mutant E3-24 of Saccharomyces cerevisiae

Cells of the E3-24 mutant of the strain D273-10B of Saccharomyces cerevisiae, grown in a fermentable substrate not showing catabolite repression of respiration (2% galactose), are able to respire, in spite of their ubiquinone deficiency in mitochondrial membranes. Mitochondria isolated from these mutant cells oxidize exogenous NADH through a pathway insensitive to antimycin A but inhibited by cyanide. Addition of methanolic solutions of ubiquinone homologs stimulates the oxidation rate and restores antimycin A sensitivity in both isolated mitochondria and whole cells. Mersalyl preincubation of isolated mitochondria inhibits both NADH oxidation and NADH-cytochrome c oxido-reductase activity (assayed in the presence of cyanide) with the same pattern. Electrons resulting from the oxidation of exogenous NADH reduce both cytochrome b5 and endogenous cytochrome c. The increase in ionic strength stimulates NADH oxidation, which is also coupled to the ATP synthesis with an ATP/O ratio similar to that obtained with ascorbate plus N,N,N',N'-tetramethyl-p-phenylendiamine (TMPD) as substrate. The effect of cyanide on these activities and on NADH-induced endogenous cytochrome c reduction is also comparable. These results support the existence in vivo and in isolated mitochondria of a energy-conserving pathway for the oxidation of cytoplasmatic NADH not related to the dehydrogenases of the inner membrane, the ubiquinone, and the b-c1 complex, but involving a cytochrome c shuttle between the NADH-cytochrome c reductase of the outer membrane and cytochrome oxidase in the inner membrane.     

Duroquinone-stimulated NADH oxidase and b type cytochromes in the plasma membrane of cauliflower and mung beans

Microsomal membrane preparations of cauliflower inflorescences and mung bean hypocotyls possess duroquinone (DQ)-stimulated NADH oxidase activities at rates of 1–10 nmol NADH · min⁻ · mg⁻. These redox reaction are associated with the endoplasmic reticulum (ER) and the plasma membrane (PM) as shown by the distributions of marker enzymes in sucrose gradients. The NADH oxidase thus partially cosediments with a specific blue light (or ascorbate) reducible b type cytochrome of the PM.Cauliflower membranes are further purified by means of an aqueous polymer two phase method. The NADH oxidase in this presumptive PM fraction is to some extent stimulated by Triton X-100 and insensitive to KCN (1 mM) or quinacrine (0.4 mM). Kinetics for DQ stimulation showed a biphasic saturation curve. These membranes also have a high FeCN reduction capacity induced by NADH but insensitive to DQ.No evidence could be found in the present study for the involvement of the specific b type cytochrome in the NADH dehydrogenase system.     

Sensitivities of the alternative respiratory components of potato tuber mitochondria to thiol reagents and Ca2+.

Plant mitochondria differ from those of mammals, since they incorporate an alternative electron transport pathway, which branches at ubiquinol to an alternative oxidase (AOX), characteristically inhibited by salicylhydroxamic acid (SHAM). Another feature of plant mitochondria is that besides complex I (EC 1.6.5.3) they possess alternative NAD(P)H-dehydrogenases insensitive to rotenone. Many stress conditions are known to alter the expression of the alternative electron transport pathway in plant mitochondria. In the present study we investigated the effects of some thiol reagents and Ca(2+) on potato mitochondrial respiratory chain presenting different activities of the alternative respiratory components AOX and external NADH dehydrogenase, a condition induced by previous treatment of potato tubers (Solanum tuberosum L., cv. Bintje) to cold stress. The results showed that Ca(2+) presented an inhibitory effect on AOX pathway in potato mitochondria energized with NADH or succinate, which was only now observed when the cytochrome pathway was inhibited by cyanide. When the cytochrome pathway was functional, Ca(2+) stimulated the external NADH dehydrogenase. Diamide was a potent AOX inhibitor and this effect was only now observed when the cytochrome pathway was inactive, as was the case for the calcium ion. Mersalyl inhibited the externally located NADH dehydrogenase and had no effect on AOX activity. The results may represent an important function of Ca(2+) on the alternative mitochondrial enzymes NADH-DH(ext) and AOX.     

Branched respiratory chain in aerobically grown Staphylococcus aureus —oxidation of ethanol by cells and protoplasts

Addition of ethanol and some other primary alcohols, except methanol, to cells and protoplasts (but not membrane particles) considerably stimulated the rate of oxygen consumption. This additional respiration was strongly inhibited by 0.1 mM KCN. The cyanide inhibition curve of endogenous substrate oxidation was slightly biphasic while in the presence of ethanol it became clearly biphasic having K _i values of approx. 0.1 and 0.5 mM. Based on the steady-state cytochrome spectra in the presence of 0.1 mM KCN, we attributed the lower K _i to cytochrome a ₆₀₂. Proteolysis of protoplasts external membrane proteins did not change the rate of endogeneous substrate oxidation but prevented the inhibition of this respiration by low concentrations of KCN and stimulation of oxygen consumption by ethanol. The activity of NAD⁺-dependent ethanol dehydrogenase in the cytoplasm was found to be 520 nmol NADH-x min^–1 x mg^–1 protein. Proteolysis of external membrane proteins apparently inhibits the operation of the cytochrome a ₆₀₂-containing electron transport branch inducing the suppression of electron flow from NADH to oxygen.     

Energy transduction in photosynthetic bacteria VI. Respiratory sites of energy conservation in membranes from dark-grown cells of Rhodopseudomonas capsulata

Membranes prepared from Rhodopseudomonas capsulata grown heterotrophically in the dark perform phosphorylation linked to oxidation of NADH and succinate, with P/2e⁻ ratios of about 0.5 and 0.15, respectively. The localization of the sites of energy conservation was investigated by observing the respiration-induced quenching of the fluorescence of atebrine.

Energization of the membrane can be demonstrated when NADH is oxidized by O₂, ferricyanide or Q₁, when succinate is oxidized by O₂ or by oxidized diaminodurene, and during the oxidation of reduced diaminodurene.

Antimycin A completely inhibits energization between succinate and O₂ or succinate and diaminodurene; however, it only inhibits partially NADH or succinate oxidases and energization between NADH and O₂. KCN inhibits NADH oxidase in a biphasic way: the first level of inhibition is observed at concentrations which block the oxidation of exogenous cytochrome c or of diaminodurene and energization between succinate or ascorbate-diaminodurene and O₂. The second level corresponds to the inhibition of the antimycin-insensitive oxidase.

The results are interpreted as evidence of the presence in these bacteria of a respiratory chain branching after the dehydrogenase system, one arm of the chain being sensitive to antimycin A and low concentrations of KCN and capable of energy conservation, the other being represented by a completely uncoupled system.     

Oxidation of NADH in a Coupled Oxidase-Peroxidase Reaction and its Significance for the Fermentation in Rumen Protozoa of the Genus Isotricha

SYNOPSIS. Cell-free extracts of the anaerobic rumen ciliate Isotricha prostoma possess a strong NADH oxidase activity. Evidence for H₂O₂ as an intermediary product during oxidation of NADH has been obtained. Gatalase activity could not be demonstrated but hydrogen peroxide is removed by a rate limiting NAD peroxidase.
In addition to oxygen several other compounds such as ferricyanide, cytochrome c , menadione and certain dyes may function as electron acceptors during oxidation of NADH. The ferricyanide reductase activity in the Isotricha extracts strongly resembles that of the mitochondrial enzyme from mammalian sources in a number of characteristics.
Partial inhibition of NADH oxidase activity was obtained with the following chelating agents: hydroxylamine, diethyl dithiocarbamate, 2,9-dimethyl-1,10-phenanthroline (DMPH), and 2-thenoyl trifluoroacetone, whereas citrate, tartrate, pyrophosphate, salicylaldoxime, EDTA and 8-hydroxyquinoline had no effect. The peroxidase was blocked completely by 0.42 mM DMPH and this inhibitor was used to block the enzyme in whole cells in experiments on oxygen toxicity. The oxidase was largely insensitive to azide, KCN, and uncouplers. Antimycin A and rotenone caused a partial inhibition of the oxidase when added in very high concentrations. ATP formation occurred during oxidation of NADH, and P/O ratios were 0.1–0.35. Addition of small amounts of oxygen to intact ciliates led to a decrease in the production of hydrogen and butyrate, while the production of acetate was increased and no change in the lactate formation was seen. This shift in fermentation end-products possibly is caused by a competition of oxygen for NADH.     

The alternative respiratory pathway of the yeast Candida parapsilosis: oxidation of exogenous NAD(P)H

The yeast Candida parapsilosis possesses two routes of electron transfer from exogenous NAD(P)H to oxygen. Electrons are transferred either to the classical cytochrome pathway at the level of ubiquinone through an NAD(P)H dehydrogenase, or to an alternative pathway at the level of cytochrome c through another NAD(P)H dehydrogenase which is insensitive to antimycin A. Analyses of mitoplasts obtained by digitonin/osmotic shock treatment of mitochondria purified on a sucrose gradient indicated that the NADH and NADPH dehydrogenases serving the alternative route were located on the mitochondrial inner membrane. The dehydrogenases could be differentiated by their pH optima and their sensitivity to amytal, butanedione and mersalyl. No transhydrogenase activity occurred between the dehydrogenases, although NADH oxidation was inhibited by NADP+ and butanedione. Studies of the effect of NADP+ on NADH oxidation showed that the NADH:ubiquinone oxidoreductase had Michaelis-Menten kinetics and was inhibited by NADP+, whereas the alternative NADH dehydrogenase had allosteric properties (NADH is a negative effector and is displaced from its regulatory site by NAD+ or NADP+).     

Respiratory energy transduction by membrane fragments of the phytopathogenic bacteria Pseudomonas cichorii and Pseudomonas aptata

The energy transduction by respiratory membranes from the fluorescent phytopathogenic bacteria Pseudomonas cichorii and Pseudomonas aptata has been examined. Both species have shown to perform ATP synthesis linked to oxidation of NADH with P/2e^- ratios ranging between 0.25 and 0.42. This phosphorylation activity is largely insensitive to antimycin A (10^-6 M) and KCN (5·10^-6 M) in membranes from P. aptata, a strain deficient in c type complement (Zannoni 1982). In contrast, the phosphorylation efficiency is partially lowered by antimycin A and KCN in P. cichorii a strain containing a branched respiratory chain (Zannoni 1982). Oxidation of NADH by ubiquinone-1 (UQ-1) in antimycin A-treated membranes from these two pseudomonads is not coupled to ATP generation. This finding indicates that both strains contain a nonenergy conserving membrane-bound NADH dehydrogenase.The location of the sites of energy conservation was investigated by respiratory-induced quenching of the fluorescence of atebrine. This approach has confirmed the P/2e^--ratios measurements along with indication of a energy conserving step at the UQ/cyt. b levels of both bacterial strains. This study has also shown that the cytochrome c oxidase activity by P. cichorii is linked to a proton gradient generation which in turn drives ATP synthesis (P/2e^-=0.1). Previous data indicated that a high-potential cytochrome of b type (cyt. b380, Em_7.0=+380 mV) is involved in the cytochrome c oxidase activity of P. cichorii (Zannoni 1982). The possibility that this bacterial strain is endowed with a terminal b type oxidase operating with a proton pump mechanism is therefore suggested.     

Regulation of Alternative Pathway Activity in Plant Mitochondria : Deviations from Q-Pool Behavior during Oxidation of NADH and Quinols

External NADH and succinate were oxidized at similar rates by soybean (Glycine max) cotyledon and leaf mitochondria when the cytochrome chain was operating, but the rate of NADH oxidation via the alternative oxidase was only half that of succinate. However, measurements of the redox poise of the endogenous quinone pool and reduction of added quinones revealed that external NADH reduced them to the same, or greater, extent than did succinate. A kinetic analysis of the relationship between alternative oxidase activity and the redox state of ubiquinone indicated that the degree of ubiquinone reduction during external NADH oxidation was sufficient to fully engage the alternative oxidase. Measurements of NADH oxidation in the presence of succinate showed that the two substrates competed for cytochrome chain activity but not for alternative oxidase activity. Both reduced Q-1 and duroquinone were readily oxidized by the cytochrome oxidase pathway but only slowly by the alternative oxidase pathway in soybean mitochondria. In mitochondria isolated from the thermogenic spadix of Philodendron selloum, on the other hand, quinol oxidation via the alternative oxidase was relatively rapid; in these mitochondria, external NADH was also oxidized readily by the alternative oxidase. Antibodies raised against alternative oxidase proteins from Sauromatum guttatum cross-reacted with proteins of similar molecular size from soybean mitochondria, indicating similarities between the two alternative oxidases. However, it appears that the organization of the respiratory chain in soybean is different, and we suggest that some segregation of electron transport chain components may exist in mitochondria from nonthermogenic plant tissues.     

Maesaquinone: a novel inhibitor of plant mitochondrial respiratory enzymes that react with ubiquinone

The effect of maesaquinone, 2-(14-nonadecenyl)-3,6-dihydroxy-5-methyl-1,4-benzoquinone, on plant mitochondrial respiration has been investigated. In mitochondria isolated from thermogenic Arum maculatum spadices, this compound inhibits both cytochrome and alternative pathway activities. Kinetic analyses reveal that this inhibition is the result of potent effects of maesaquinone on the alternative oxidase (ID50 < 0.3 microM) and complex III (ID50 < 5 microM). Succinate dehydrogenase and external NADH dehydrogenase are also inhibited, albeit to a lesser extent (approximately 30% at 1 microM). These data suggest that maesaquinone specifically affects the interaction of the respective enzymes with ubiquinone.     

Direct Inhibition of Plant Mitochondrial Respiration by Elevated CO2

Doubling the concentration of atmospheric CO2 often inhibits plant respiration, but the mechanistic basis of this effect is unknown. We investigated the direct effects of increasing the concentration of CO2 by 360 [mu]L L-1 above ambient on O2 uptake in isolated mitochondria from soybean (Glycine max L. cv Ransom) cotyledons. Increasing the CO2 concentration inhibited the oxidation of succinate, external NADH, and succinate and external NADH combined. The inhibition was greater when mitochondria were preincubated for 10 min in the presence of the elevated CO2 concentration prior to the measurement of O2 uptake. Elevated CO2 concentration inhibited the salicylhydroxamic acid-resistant cytochrome pathway, but had no direct effect on the cyanide-resistant alternative pathway. We also investigated the direct effects of elevated CO2 concentration on the activities of cytochrome c oxidase and succinate dehydrogenase (SDH) and found that the activity of both enzymes was inhibited. The kinetics of inhibition of cytochrome c oxidase were time-dependent. The level of SDH inhibition depended on the concentration of succinate in the reaction mixture. Direct inhibition of respiration by elevated CO2 in plants and intact tissues may be due at least in part to the inhibition of cytochrome c oxidase and SDH.     

The oxidation of glucose by Acinetobacter calcoaceticus: interaction of the quinoprotein glucose dehydrogenase with the electron transport chain

The coupling of the quinoprotein glucose dehydrogenase to the electron transport chain has been investigated in Acinetobacter calcoaceticus. No evidence was obtained to support a previous suggestion that the soluble form of the dehydrogenase and the soluble cytochrome b associated with it are involved in the oxidation of glucose. Analysis of cytochrome content, and of reduction of cytochromes in membranes by substrates, and of sensitivity to cyanide indicated that glucose, succinate and NADH are all oxidized by way of the same b-type cytochrome(s) and cytochrome oxidases (cytochrome o and cytochrome d). Mixed inhibition studies [with KCN and hydroxyquinoline N-oxide (HQNO)] showed that the b-type cytochrome(s) formed a binary complex with the o-type oxidase and that there was thus no communication between the electron transport chains at the cytochrome level. Measurements of the reduction of ubiquinone-9 by glucose and NADH, and inhibitor studies using HQNO, indicated that the ubiquinone mediates electron transport from both the glucose and NADH dehydrogenases. In some conditions the quinone pool facilitated communication between the 'glucose oxidase' and 'NADH oxidase' electron transport chains, but in normal conditions these chains were kinetically distinct.     

Effect of water deficit on respiration of conducting bundles in leaf petioles of sugar beet

Isolated fibrovascular bundles from source leaf petioles of sugar beet (Beta vulgaris L.) and hog-weed (Heracleum sosnovskyi L.) were used to study the influence of long-term drought on the oxygen uptake rate and activities of mitochondrial oxidases, i.e., cytochrome oxidase and salicylhydroxamic acid-sensitive alternative oxidase (AO). Under normal soil moisture content (70% of full water-retaining capacity, WRC), the oxygen uptake by sugar beet conducting bundles was characterized by a high rate (> 700 μl O₂/(g fr wt h)) and by distinct cytochrome oxidase-dependent manner of terminal oxidation (up to 80% inhibition of respiration in the presence of 0.5 mM KCN). After long-term water deficit (40% of WRC), the bundle respiration proceeded at nearly the same rate but featured an elevated resistance to cyanide. At early drought stage (10 days), a decrease in the activity of cytochrome-mediated oxidation pathway was largely counterbalanced by activation of mitochondrial AO, whereas long-term dehydration of plants was accompanied by activation of additional oxidative systems insensitive to both KCN and SHAM. Similar but even more pronounced changes in activities of terminal oxidases were discovered in conducting bundles of wild-grown hogweed plants exposed to long-term natural drought. It is supposed that the suppression of cytochrome-mediated oxidation coupled with ATP synthesis in the cells of sugar beet source leaves impedes the translocation of assimilates and their accumulation in the taproot, which represents an important factor of drastic decrease in the yield of this agricultural crop under conditions of water deficit.     

ATP synthesis during exogenous NADH oxidation. A reappraisal

This paper reports a reinvestigation on the pathway for mitochondrial oxidation of exogenous NADH and on the related ATP synthesis, first reported 30 years ago (Lehninger, A.L. (1951) J. Biol. Chem. 190, 345-359). NADH oxidation, both in intact and in water-treated mitochondria, is 90% inhibited by mersalyl, an inhibitor of the outer membrane NADH-cytochrome b5 reductase, and 10% inhibited by rotenone. The mersalyl-sensitive, but not the rotenone-sensitive, portion of NADH oxidation is stimulated by exogenous cytochrome c. Part of ATP synthesis is independent of exogenous NADH and cytochrome c, and is inhibited by rotenone and antimycin A, and is therefore due to oxidation of endogenous substrates. Another part of ATP synthesis is dependent on exogenous NADH and cytochrome c, is insensitive to rotenone and antimycin A, and is due to operation of cytochrome oxidase. It is concluded that (i) oxidation of exogenous NADH in the presence of cytochrome c proceeds mostly through NADH-cytochrome b5 reductase and cytochrome b5 on the outer membrane and then through cytochrome oxidase via the cytochrome c shuttle, and (ii) ATP synthesis during oxidation of exogenous NADH is partly due to oxidation of endogenous substrates and partly to operation of cytochrome oxidase receiving electrons from the outer membrane via cytochrome c.     

During the stationary growth phase, Yarrowia lipolytica prevents the overproduction of reactive oxygen species by activating an uncoupled mitochondrial respiratory pathway

In the branched mitochondrial respiratory chain from Yarrowia lipolytica there are two alternative oxido-reductases that do not pump protons, namely an external type II NADH dehydrogenase (NDH2e) and the alternative oxidase (AOX). Direct electron transfer between these proteins is not coupled to ATP synthesis and should be avoided in most physiological conditions. However, under low energy-requiring conditions an uncoupled high rate of oxygen consumption would be beneficial, as it would prevent overproduction of reactive oxygen species (ROS). In mitochondria from high energy-requiring, logarithmic-growth phase cells, most NDH2e was associated to cytochrome c oxidase and electrons from NADH were channeled to the cytochromic pathway. In contrast, in the low energy requiring, late stationary-growth phase, complex IV concentration decreased, the cells overexpressed NDH2e and thus a large fraction of this enzyme was found in a non-associated form. Also, the NDH2e-AOX uncoupled pathway was activated and the state IV external NADH-dependent production of ROS decreased. Association/dissociation of NDH2e to/from complex IV is proposed to be the switch that channels electrons from external NADH to the coupled cytochrome pathway or allows them to reach an uncoupled, alternative, ΔΨ-independent pathway.     

Alternative Cyanide-sensitive Oxidase Interacting with Photosynthesis in Synechocystis PCC6803. Ancestor of the Terminal Oxidase of Chlororespiration?

Influence of respiration on photosynthesis in Synechocystis PCC6803 was studied by measuring the redox transients of cytochrome f (cyt f) upon excitation of the cells with repetitive single turnover flashes. Upon the addition of KCN the flash-induced oxidation of cyt f was increased and the rereduction of cyt f+ was accelerated. Dependence of these effects on the concentration of KCN clearly demonstrated the existence of two cyanide-sensitive oxidases interacting with photosynthesis: cyt aa3, which was sensitive to low concentrations of cyanide, and an alternative oxidase, which could be suppressed by using 1 mM KCN. The interaction between the photosynthetic and the respiratory electron transport chains was regulated mainly by the activity of the alternative cyanide-sensitive oxidase. The oxidative pathway involving the alternative cyanide-sensitive oxidase was insensitive to salicyl hydroxamic acid and azide. The close resemblance of the inhibition pattern reported here and that described for chlororespiration in algae and higher plants strongly suggest that an oxidase of the same type as the alternative cyanide-sensitive oxidase of cyanobacteria functions as a terminal oxidase in chloroplasts.     

Pyruvate metabolism in castor-bean mitochondria.

We report the isolation of mitochondria from the endosperm of castor beans (Ricinus communis). These mitochondria oxidized succinate, external NADH, malate and pyruvate with respiratory-control and ADP/O ratios consistent with those found previously with mitochondria from other plant sources. The mitochondria exhibited considerable sensitivity to the electron-transport-chain inhibitors antimycin A and cyanide when oxidizing succinate and external NADH. Pyruvate-dependent O2 uptake was relatively insensitive to these inhibitors, although the residual O2 uptake could be inhibited by salicylhydroxamic acid. We conclude that a cyanide-insensitive alternative terminal oxidase is functional in these mitochondria. However, electrons from the succinate dehydrogenase or external NADH dehydrogenase seem to have no access to this pathway. There is little interconnection between the salicylhydroxamic acid-sensitive and cyanide-sensitive pathways of electron transport. alpha-Cyanocinnamate and its analogues, compound UK5099 [alpha-cyano-beta-(1-phenylindol-3-yl)acrylate] and alpha-cyano-4-hydroxycinnamate, were all found to be potent non-competitive inhibitors of pyruvate oxidation in castor-bean mitochondria. The accumulation of pyruvate by castor-bean mitochondria was determined by using a silicone-oil-centrifugation technique. The accumulation was shown to observe Michaelis-Menten kinetics, with a Km for pyruvate of 0.10 mM and a Vmax. of 0.95 nmol/min per mg of mitochondrial protein. However, the observed rates of pyruvate accumulation were insufficient to account for the pyruvate oxidation rates found in the oxygen-electrode studies. We were able to demonstrate that this is due to the immediate export of the accumulated radiolabel in the form of malate and citrate. Compound UK5099 inhibited the accumulation of [2-14C]pyruvate by castor-bean mitochondria at concentrations similar to those required to inhibit pyruvate oxidation.     

异源表达NADH选择性氧化酶提高光滑球拟酵母酵解速率及丙酮酸生产强度

摘要：【目的】为进一步提高光滑球拟酵母(Torulopsis glabrata)葡萄糖代谢速率及丙酮酸生产强度。【方法】将源于荚膜胞浆菌(Histoplasma capsulatum)的编码选择性氧化酶的AOX1基因过量表达于T. glabrata中,获得了一株线粒体内NADH氧化途径发生改变且胞内总NADH 氧化酶活性提高1.8倍的重组菌株AOX。【结果】与出发菌株CON比较,细胞浓度以及发酵周期降低了20.3%和10.7%,而平均比葡萄糖消耗速率和丙酮酸合成速率分别提高了34.7%和54.1%。其原因