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1.
Ilyobacter delafieldii produced an extracellular poly--hydroxybutyrate (PHB) depolymerase when grown on PHB; activity was not detected in cultures grown on 3-hydroxybutyrate, crotonate, pyruvate or lactate. PHB depolymerase activity was largely associated with the PHB granules (supplied as growth substrate), and only 16% was detected free in the culture supernatant. Monomeric 3-hydroxybutyrate was detectable as a product of depolymerase activity. The monomer was fermented to acetate, butyrate and H2. After activation by coenzyme A transfer from acetyl-CoA or butyryl-CoA, the resultant 3-hydroxybutyryl-CoA was oxidized to acetoacetyl-CoA (producing NADH), followed by thiolytic cleavage to yield acetyl-CoA which was further metabolized to acetyl-phosphate, then to acetate with concomitant ATP production. The reducing equivalents (NADH) could be disposed of by the evolution of H2, or by a reductive pathway in which 3-hydroxybutyryl-CoA was dehydrated to crotonyl-CoA and reduced to butyryl-CoA. In cocultures ofI. delafieldii withDesulfovibrio vulgaris on PHB, the H2 partial pressure was much lower than in the pure cultures, and sulfide was produced. Thus interspecies hydrogen transfer caused a shift to increased acetate and H2 production at the expense of butyrate. 相似文献
2.
Félix Busto Joaquin Soler Dolores de Arriaga Eduardo Cadenas 《Archives of microbiology》1984,139(2-3):255-259
Some kinetic properties of the D(-)-lactate dehydrogenase (EC 1.1.1.28) of Escherichia coli have been investigated. There were marked differences between the kinetic properties of the enzyme studied in situ compared with the in vitro D(-)-lactate dehydrogenase. D(-)-Lactate dehydrogenase in situ showed high substrate inhibition with pyruvate over the pH range 6.0–7.0, whereas the enzyme in vitro did not. The pH optimum for pyruvate reduction by the in situ D(-)-lactate dehydrogenase ranged between pH 7.5 and 7.8, whereas the in vitro enzyme showed its pH optimum between pH 6.8 and 7.0. The pK values of the prototropic groups that controlled the enzymatic activity shift to the acidic region for the in vitro enzyme with respect to the in situ enzyme. In vitro D(-)-lactate dehydrogenase exhibits homotropic interactions with its substrate, pyruvate and its coenzyme, NADH, at pH values ranging between pH 6.0 and 8.5, but the in situ enzyme showed homotropic interactions neither with pyruvate nor with NADH at all pH values studied. 相似文献
3.
Summary It was found that dl-lactate, acetate, pyruvate, succinate, fumarate, malate, oxalacetate and L-aspartate stimulated considerably the production of the antitumor L-asparaginase EC-2 by a colicinogenic strain of E. coli in Tryptone medium. While in the absence of these stimulative substances enzyme production was about 0.01 IU/mg dry weight, it reached 0.57–1.18 IU/mg in the presence of the substances named above. Maximum effects were obtained at the concentrations 0.025–0.1 M; at higher concentrations enzyme production decreased. L-asparagine raised the enzyme production from 0.05 IU/mg to 0.70 IU/mg; in order to obtain this effect, however, it was necessary to lower the oxygen absorption rate. Citrate and -ketoglutarate had no stimulatory effect; the effect of L-glutamate was negligible. In the cases of dl-lactate, pyruvate and L-aspartate the dependence of stimulatory effects on the time of addition of the stimulants was studied. It was found that in the case of pyruvate and especially of dl-lactate enzyme production increased rapidly between the 4 and 6 h of cultivation, i.e. at the end of the exponential growth phase; it did not matter whether the stimulant had been added at zero, 2 or 4 h of cultivation. In the case of L-aspartate the situation was principally similar, though the enzyme production started later and increased more slowly. 相似文献
4.
Klebsiella aerogenes NCTC418 was cultured anaerobically under glucose-limited conditions in chemostat cultures at various growth rates, ranging from 0.13 h-1 to 0.82 h-1. It was found that the specific uptake rate of glucose varied linearly with the growth rate and that under these conditions glucose was fermented solely to acetate and ethanol plus CO2+H2 and formate.When steady-state cultures were pulsed with cell saturating concentrations of glucose, the specific glucose aptake rate increased immediately and substantially. However, at steady-state growth rates lower than 0.5 h-1, this increase was not accompanied by a change in the growth rate, in contrast to cultures growing at higher rates. It was found that relief of the glucose limitation resulted in a shift in fermentation pattern: at the lower growth rates 50% or more of the extra glucose taken up was fermented to D-lactate.Incubation experiments with sonified cells revcaled that K. aerogenes possessed all the enzymes needed to convert dihydroxyacetone phosphate to methylglyoxal and subsequently to D-lactate, and that the rate at which this overall conversion occurred in vitro was in close agreement with the production rate of D-lactate in vivo. Moreover, it was found that the activities of the enzymes of the methylglyoxal bypass were dependent on the imposed growth rate. At higher growth rates, where cells possessed the potential to increase their growth rate immediately, the activity of methylglyoxal synthase was relatively low.it could be shown that, under low growth rate conditions, the uncoupling effect of the methylglyoxal bypass was highly effective and that, as a consequence thereof, a significant increase in the uptake rate of the energy source was accompanied by only a marginal increase in the rate at which ATP was synthesized. 相似文献
5.
Joo Sang Yeo Jae Yeon Park Sung Ho Yeom Young Je Yoo 《Biotechnology and Bioprocess Engineering》2008,13(1):14-24
Gluconate and glucose were selected as the carbon substrates in the production of poly-3-hydroxybutyrate (PHB). Gluconate
was utilized to maximize the specific growth rate during the first stage of cell growth, whereas glucose was used to maximize
PHB biosynthesis during the second stage of PHB accumulation. The sequential feeding of gluconate and glucose resulted in
a 50% enhancement of PHB productivity as compared to the cultures cultivated on glucose alone. In conjunction with secondary
glucose uptake, the presence of a trace amount of ammonium increased the rate of PHB biosynthesis during the stage of PHB
accumulation. Via the feeding of 0.03 mmol/h of NH4Cl solution prior to the exhaustion of the initial amount of NH4Cl, PHB productivity was significantly enhanced as compared to the cultures raised on glucose alone. The glucose-grown culture
evidenced a higher level of NADPH during the NH4Cl-exausted PHB accumulation stage than was observed in the gluconate-grown culture, which reflects that the reason of higher
PHB production observed when glucose was used as a carbon source. NH4Cl feeding following the depletion of initial NH4Cl resulted in elevated levels of both ATP and NADPH, which increased the PHB biosynthesis rate, and also in a decrease in
the level of NADH, which reflected the alleviation of the inhibitory effects on the cells caused by nitrogen depletion.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
6.
Fermentation of trans-aconitate via citrate,oxaloacetate, and pyruvate by Acidaminococcus fermentans
Growing cells of Acidaminococcus fermentans (DSM 20731 and ATCC 25085) fermented trans-aconitate via citrate, oxaloacetate, and pyruvate to approximately 2 CO2, 1.8 acetate, 0.1 butyrate and 0.9 H2. The carbon and electron recoveries were close to 100%. On citrate no growth was observed and washed cells were unable to
ferment this tricarboxylate. In cell-free extracts, however, citrate as well as trans-aconitate were readily fermented to CO2 and acetate. Under these conditions, also cis-aconitate, oxaloacetate, and pyruvate were formed, whereas butyrate and intermediates of glutamate fermentation, 2-oxoglutatrate
and glutaconate, could not be detected. Citrate Si-lyase, a Mg2+-dependent oxaloacetate decarboxylase, and pyruvate synthase were present in quantities that corresponded to the growth rate
of the organism.
Received: 3 May 1996 / Accepted: 12 August 相似文献
7.
Andreas Jahn Barbara Keuntje Michael Dörffler Werner Klipp Jürgen Oelze 《Applied microbiology and biotechnology》1994,40(5):687-690
In Rhodobacter capsulatus, the hupL gene encoding the large subunit of the uptake-hydrogenase (Hup) enzyme complex was mutated by insertion of an interposon. The mutant neither synthesized an active hydrogenase nor grew photoautotrophically. Under conditions of nitrogen (N) limitation, photoheterotrophic cultures of the wild type and the mutant evolved H2 by activity of the nitrogenase enzyme complex. When grown with glutamate as an N source and either d,l-malate or l-lactate as carbon sources, the efficiency of H2 production by the HupL mutant was higher than 90%, whereas wild-type cultures exhibited efficiencies of 54% (with d,l-malate) and 64% (with l-lactate), respectively. With NH
inf4
sup+
as the N source, efficiencies of H2 production were 70% (mutant) and 52% (wild type).
Correspondence to: J. Oelze 相似文献
8.
K. Sonntag J. Schwinde A. A. de Graaf A. Marx B. J. Eikmanns W. Wiechert H. Sahm 《Applied microbiology and biotechnology》1995,44(3-4):489-495
The carbon flux distribution in the central metabolism of Corynebacterium glutamicum was studied in batch cultures using [1-13C]- and [6-13C]glucose as substrate during exponential growth as well as during overproduction of l-lysine and l-glutamate. Using the 13C NMR data in conjunction with stoichiometric metabolite balances, molar fluxes were quantified and normalised to the glucose uptake rate, which was set to 100. The normalised molar flux via the hexose monophosphate pathway was 40 during exponential growth, whereas it was only 17 during l-glutamate production. During l-lysine production, the normalised hexose monophosphate pathway flux was elevated to 47. Thus, the carbon flux via this pathway correlated with the NADPH demand for bacterial growth and l-lysine overproduction. The normalised molar flux in the tricarboxylic acid cycle at the level of 2-oxoglutarate dehydrogenase was 100 during exponential growth and 103 during l-lysine secretion. During l-glutamate formation, the normalised flux through the tricarboxylic acid cycle was reduced to 60. In contrast to earlier NMR studies with C. glutamicum, no significant activity of the glyoxylate pathway could be detected. All experiments indicated a strong in vivo flux from oxaloacetate back to phosphoenolpyruvate and/or pyruvate, which might be due to phosphoenolpyruvate carboxykinase activity in C. glutamicum. 相似文献
9.
This study aimed at increasing the pyruvate productivity of a multi-vitamin auxotrophic yeast Torulopsis glabrata by redirecting NADH oxidation from adenosine triphosphate (ATP)-production pathway (oxidative phosphorylation pathway) to non-ATP production pathway (fermentative pathway). Two respiratory-deficient mutants, RD-17 and RD-18, were screened and selected after ethidium bromide (EtBr) mutagenesis of the parent strain T. glabrata CCTCC M202019. Compared with the parent strain, cytochrome aa
3 and b in electron transfer chain (ETC) of RD-18 and cytochrome b in RD-17 were disrupted. As a consequence, the activities of key ETC enzymes of the mutant RD-18, including F0F1-ATP synthase, complex I, complex I + III, complex II + III, and complex IV, decreased by 22.2, 41.6, 53.1, 23.6, and 84.7%, respectively. With the deficiency of cytochromes in ETC, a large amount of excessive cytosolic NADH was accumulated, which hampered the further increase of the glycolytic flux. An exogenous electron acceptor, acetaldehyde, was added to the strain RD-18 culture to oxidize the excessive NADH. Compared with the parent strain, the concentration of pyruvate and the glucose consumption rate of strain RD-18 were increased by 26.5 and 17.6%, respectively, upon addition of 2.1 mM of acetaldehyde. The strategy for increasing the glycolytic flux in T. glabrata by redirecting the NADH oxidation pathway may provide an alternative approach to enhance the glycolytic flux in yeast. 相似文献
10.
Cyanide inhibited d- and l-lactate and NADH oxidase activities of membrane particles from Propionibacterium shermanii but only at relatively high concentrations. Inhibition occurred at two different sites in the electron transport pathway. One site, with a half-maximal inhibition concentration (I
0.5) of 2 to 3 mM KCN, is located at the terminal oxidase involved in cytochrome b oxidation; the evidence is consistent with cytochrome d being the major oxidase involved. At high concentrations, cyanide inhibited reduction of cytochrome b by d-lactate (I
0.5 value 20–25 mM cyanide). A proportion of the oxygen-uptake remained uninhibited even by 100 mM cyanide; this proportion was about 80% for succinate, 30% for l-lactate, 15% for d-lactate and 10% for NADH. The oxygen uptake per mol of substrate oxidised increased with increasing cyanide concentration and was accompanied by the formation of hydrogen peroxide as a product of a cyanide-insensitive oxidase system.Abbreviations PMS
Phenazine methosulphate 相似文献
11.
The effect of gene knockout on metabolism in the pflA–, pflB–, pflC–, and pflD– mutants of Escherichia coli was investigated. Batch cultivations of the pfl
– mutants and their parent strain were conducted using glucose as a carbon source. It was found that pflA– and pflB– mutants, but not pflC– and pflD– mutants, produced large amounts of d-lactate from glucose under the microaerobic condition, and the maximum yield was 73%. In order to investigate the metabolic regulation mechanism, we measured enzyme activities for the following eight enzymes: glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), pyruvate kinase, lactate dehydrogenase (LDH), phosphoenolpyruvate carboxylase, acetate kinase, and alcohol dehydrogenase. Intracellular metabolite concentrations of glucose 6-phosphate, fructose 1,6-bisphosphate, phosphoenolpyruvate, pyruvate, acetyl coenzyme A as well as ATP, ADP, AMP, NADH, and NAD+ were also measured. It was shown that the GAPDH and LDH activities were considerably higher in pflA– and pflB– mutants, which implies coupling between NADH production and consumption between the two corresponding reactions. The urgent energy requirement was shown by the lower ATP/AMP level due to both oxygen limitation and pfl gene knockout, which promoted significant stepping-up of glycolysis when using glucose as a carbon source. It was shown that the demand for energy is more important than intracellular redox balance, thus excess NADH produced through GAPDH resulted in a significantly higher intracellular NADH/NAD+ ratio in pfl
– mutants. Consequently, the homolactate production was achieved to meet the requirements of the redox balance and the energy production through glycolysis. The effect of using different carbon sources such as gluconate, pyruvate, fructose, and glycerol was investigated. 相似文献
12.
Sigrun Feldmann Georg A. Sprenger Hermann Sahm 《Applied microbiology and biotechnology》1989,31(2):152-157
Summary Grown anaerobically on d-xylose, Klebsiella planticola ATCC 33531 produced acetate, formate, lactate, CO2 and ethanol as major end-products. A Mu-insertion mutant which lacked pyruvate-formate-lyase showed among its fermentation products more than 70% d-lactate with residual acetate, 2,3-butanediol, and traces of ethanol, formate, and CO2. After the introduction of a plasmid carrying the gene for the enzyme pyruvate decarboxylase from Zymomonas mobilis, this Klebsiella mutant became an efficient ethanol producer. The recombinant strain produced 387 mM ethanol from 275 mM xylose in 80 h, about 83% of the theoretical maximal yield. Furthermore, this mutant consumed more than double the amount of xylose (41 g/l) compared to the wild-type, due to reduced production of inhibiting acids during growth.Dedicated to Professor Dr. Zähner on the occasion of his 60th birthday 相似文献
13.
Flux through Citrate Synthase Limits the Growth of Ethanologenic Escherichia coli KO11 during Xylose Fermentation 总被引:1,自引:0,他引:1
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S. A. Underwood M. L. Buszko K. T. Shanmugam L. O. Ingram 《Applied microbiology》2002,68(3):1071-1081
Previous studies have shown that high levels of complex nutrients (Luria broth or 5% corn steep liquor) were necessary for rapid ethanol production by the ethanologenic strain Escherichia coli KO11. Although this strain is prototrophic, cell density and ethanol production remained low in mineral salts media (10% xylose) unless complex nutrients were added. The basis for this nutrient requirement was identified as a regulatory problem created by metabolic engineering of an ethanol pathway. Cells must partition pyruvate between competing needs for biosynthesis and regeneration of NAD+. Expression of low-Km Zymomonas mobilis pdc (pyruvate decarboxylase) in KO11 reduced the flow of pyruvate carbon into native fermentation pathways as desired, but it also restricted the flow of carbon skeletons into the 2-ketoglutarate arm of the tricarboxylic acid pathway (biosynthesis). In mineral salts medium containing 1% corn steep liquor and 10% xylose, the detrimental effect of metabolic engineering was substantially reduced by addition of pyruvate. A similar benefit was also observed when acetaldehyde, 2-ketoglutarate, or glutamate was added. In E. coli, citrate synthase links the cellular abundance of NADH to the supply of 2-ketoglutarate for glutamate biosynthesis. This enzyme is allosterically regulated and inhibited by high NADH concentrations. In addition, citrate synthase catalyzes the first committed step in 2-ketoglutarate synthesis. Oxidation of NADH by added acetaldehyde (or pyruvate) would be expected to increase the activity of E. coli citrate synthase and direct more carbon into 2-ketoglutarate, and this may explain the stimulation of growth. This hypothesis was tested, in part, by cloning the Bacillus subtilis citZ gene encoding an NADH-insensitive citrate synthase. Expression of recombinant citZ in KO11 was accompanied by increases in cell growth and ethanol production, which substantially reduced the need for complex nutrients. 相似文献
14.
《Journal of Fermentation and Bioengineering》1994,77(1):97-99
Citrate (si)-synthase (citrate oxaloacetate-lyase, EC 4.1.3.7) was purified as an electrophoretically homogeneous protein from a nitrite-oxidizing chemoautotrophic bacterium, Nitrobacter agilis ATCC 14123. The molecular mass (Mr) of the native enzyme was estimated to be about 250,000 by gel filtration, whereas SDS-PAGE gave two bands with Mr values of 45,000 and 80,000, respectively, suggesting that the enzyme is a tetramer consisting of two different subunits (α: 45,000, β: 80,000). The isoelectric point of the enzyme was 5.4. The pH and temperature optima on the citrate synthase activity were about 7.5–8.0 and 30–35°C, respectively. The citrate synthase was stable in the pH range of 6.0–9.0 and up to 55°C. The apparent Km values for oxaloacetate and acetyl-CoA were about 27 μM and 410 μM, respectively. The activity of citrate synthase was not inhibited by ATP (1 mM), NADH (1 mM) or 2-oxoglutarate (10 mM), but was strongly inhibited by SDS (1 mM). Activation by metal ions was not observed. 相似文献
15.
Bradyrhizobium japonicum, the nitrogen-fixing symbiotic partner of soybean, was grown on various carbon substrates and assayed for the presence of
the glyoxylate cycle enzymes, isocitrate lyase and malate synthase. The highest levels of isocitrate lyase [165–170 nmol min–1 (mg protein)–1] were found in cells grown on acetate or β-hydroxybutyrate, intermediate activity was found after growth on pyruvate or galactose,
and very little activity was found in cells grown on arabinose, malate, or glycerol. Malate synthase activity was present
in arabinose- and malate-grown cultures and increased by only 50–80% when cells were grown on acetate. B. japonicum bacteroids, harvested at four different nodule ages, showed very little isocitrate lyase activity, implying that a complete
glyoxylate cycle is not functional during symbiosis. The apparent K
m of isocitrate lyase for d,l-isocitrate was fourfold higher than that of isocitrate dehydrogenase (61.5 and 15.5 μM, respectively) in desalted crude extracts
from acetate-grown B. japonicum. When isocitrate lyase was induced, neither the V
max nor the d,l-isocitrate K
m of isocitrate dehydrogenase changed, implying that isocitrate dehydrogenase is not inhibited by covalent modification to
facilitate operation of the glyoxylate cycle in B. japonicum.
Received: 10 October 1997 / Accepted: 16 January 1998 相似文献
16.
The ldh gene of Corynebacterium glutamicum ATCC 13032 (gene symbol cg3219, encoding a 314 residue NAD+-dependent l-(+)-lactate dehydrogenase, EC 1.1.1.27) was cloned into the expression vector pKK388-1 and over-expressed in an ldhA-null E. coli TG1 strain upon isopropyl-β-D-thiogalactopyranoside (IPTG) induction. The recombinant protein (referred to here as CgLDH)
was purified by a combination of dye-ligand and ion-exchange chromatography. Though active in its absence, CgLDH activity
is enhanced 17- to 20-fold in the presence of the allosteric activator d-fructose-1,6-bisphosphate (Fru-1,6-P2). Contrary to a previous report, CgLDH has readily measurable reaction rates in both directions, with V
max for the reduction of pyruvate being approximately tenfold that of the value for l-lactate oxidation at pH 7.5. No deviation from Michaelis–Menten kinetics was observed in the presence of Fru-1,6-P2, while a sigmoidal response (indicative of positive cooperativity) was seen towards l-lactate without Fru-1,6-P2. Strikingly, when introduced into an lldD
− strain of C. glutamicum, constitutively expressed CgLDH enables the organism to grow on l-lactate as the sole carbon source. 相似文献
17.
Activation of Respiration to Support Dark NO(3) and NH(4) Assimilation in the Green Alga Selenastrum minutum
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Short-term changes in pyridine nucleotides and other key metabolites were measured during the onset of NO3− or NH4+ assimilation in the dark by the N-limited green alga Selenastrum minutum. When NH4+ was added to N-limited cells, the NADH/NAD ratio rose immediately and the NADPH/NADP ratio followed more slowly. An immediate decrease in glutamate and 2-oxoglutarate indicates an increased flux through the glutamine synthase/glutamate oxoglutarate aminotransferase. Pyruvate kinase and phosphoenolpyruvate carboxylase are rapidly activated to supply carbon skeletons to the tricarboxylic acid cycle for amino acid synthesis. In contrast, NO3− addition caused an immediate decrease in the NADPH/NADP ratio that was accompanied by an increase in 6-phosphogluconate and decrease in the glucose-6-phosphate/6-phosphogluconate ratio. These changes show increased glucose-6-phosphate dehydrogenase activity, indicating that the oxidative pentose phosphate pathway supplies some reductant for NO3− assimilation in the dark. A lag of 30 to 60 seconds in the increase of the NADH/NAD ratio during NO3− assimilation correlates with a slow activation of pyruvate kinase and phosphoenolpyruvate carboxylase. Together, these results indicate that during NH4+ assimilation, the demand for ATP and carbon skeletons to synthesize amino acid signals activation of respiratory carbon flow. In contrast, during NO3− assimilation, the initial demand on carbon respiration is for reductant and there is a lag before tricarboxylic acid cycle carbon flow is activated in response to the carbon demands of amino acid synthesis. 相似文献
18.
Themis-Dimitrios Kyprianou Hans O. Pörtner Andreas Anestis Basile Kostoglou Konstantinos Feidantsis Basile Michaelidis 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(7):1005-1018
The winter syndrome in the gilthead sea bream Sparus aurata indicates that the species is exposed to critically low temperatures in Mediterranean aquaculture in winter. The present
study of metabolic patterns and molecular stress responses during cold exposure was carried out to investigate this “disease”,
in light of the recent concept of oxygen and capacity limited thermal tolerance. The metabolic profile of fuel oxidation was
examined by determining the activities of the enzymes hexokinase (HK), aldolase (Ald), pyruvate kinase (PK), l-lactate dehydrogenase (l-LDH), citrate synthase (CS), malate dehydrogenase (MDH) and 3-hydroxyacyl CoA dehydrogenase (HOAD) in heart, red and white
muscle after exposure to temperatures of 10, 14 and 18°C. Especially, the increase in LDH activity combined with the accumulation
of l-lactate in tissues indicates that temperatures below 14°C are critical for Sparus aurata and stimulate the anaerobic component of metabolism. Increase in the activity of HOAD suggests that oxidation of free fatty
acids might contribute to ATP turnover at low temperatures. The expression of Hsp70 and Hsp90 in all tissues examined revealed
a cellular stress response during cooling below 18°C. In the light of winter temperatures in S. aurata cultures around 10°C, our data suggest that the fish are exposed to stressful conditions at the low end of their thermal
tolerance window. These conditions likely impair the aerobic capacity of the fish, compromise the rates of growth and reproduction
and may contribute to elicit pathological conditions. 相似文献
19.
ELMER MARTIN MICHAEL W. SIMON FRANK W. SCHAEFER ANTONY J. MUKKADA 《The Journal of eukaryotic microbiology》1976,23(4):600-607
SYNOPSIS. The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania (L. brasiliensis, L. donovani, L. mexicana, and L. tropica) were compared. These organisms possess enzymes of the Embden-Meyerhof pathway but lack lactate dehydrogenase. No evidence could be found for the production of lactic acid by growing cultures and lactic acid could not be detected either in cell-free preparations or after incubation of cell-free extracts with pyruvate and NADH under appropriate conditions. All 4 species possess α-glycerophosphate dehydrogenase and α-glycerophosphate phosphatase which together could regenerate NAD, thus compensating for the absence of lactate dehydrogenase. The oxidative and nonoxidative reactions of the hexose monophosphate pathway are present in all 4 species. Cell-free extracts have pyruvate dehydrogenase activity which allows the entry of pyruvate into and its subsequent oxidation through the tricarboxylic acid cycle. All enzymes of this cycle, including a thiamine pyrophosphate dependent α-ketoglutarate dehydrogenase are present. Both NAD and NADP-linked malate dehydrogenase activities are present. The isocitrate dehydrogenase is NADP specific. There is an active glutamate dehydrogenase which could compete with α-ketoglutarate dehydrogenase for the common substrate (α-ketoglutarate). Replenishment of C4 acids is accomplished by heterotrophic CO2 fixation catalyzed by pyruvate carboxylase. All 4 species have high levels of NADH oxidase activity. Several enzymes thus far not found in any species of Leishmania have been demonstrated. These are: phosphoglucose isomerase, triose phosphate isomerase, fructose-1, 6-diphosphatase, 3-phosphoglycerate kinase, enolase, α-glycerophosphate dehydrogenase, α-glycerophosphate phosphatase, pyruvate dehydrogenase complex, citrate synthase, aconitase, α-ketoglutarate dehydrogenase, glutamate dehydrogenase, and NADH oxidase. 相似文献
20.
Alfons J. M. Stams Diderik R. Kremer Klaas Nicolay Gerard H. Weenk Theo A. Hansen 《Archives of microbiology》1984,139(2-3):167-173
Whole cells of Desulfobulbus propionicus fermented [1-13C]ethanol to [2-13C] and [3-13C]propionate and [1-13C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA: pyruvate transacetylase, acetase kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activity of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence of pyruvate, CoA and ATP and the oxaloacetate-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor.The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.Abbreviations DCPIP
2,6-dichlorophenolindophenol
- PEP
phosphoenolpyruvate 相似文献