The occurrence of the Entner-Doudoroff pathway in bacteria

The occurrence of the two key enzymes of the Entner-Doudoroff pathway, gluconate-6-phosphate dehydrase and 2-keto-3-deoxygluconate-6-phosphate aldolase, was determined in approximately 150 strains belonging to 37 different bacterial genera. The following results were obtained:

1. 24 out of 37 genera have at least one representative with the Entner-Doudoroff mechanism. It is thus more widespread than previously thought.
2. The Entner-Doudoroff mechanism occurs mainly in gram-negative bacteria with a DNA base composition in the range 52–70% GC. Eighty-five per cent of these organisms contain the system, while only 20% (6 strains) of the gram-negative organisms with less than 52% GC possess both enzymes.
3. This pathway is absent in all gram-positive organisms investigated except in 5 out of 12Nocardia strains.
4. Erwinia and some strains of theAchromobacter-Alcaligenes group are exceptional, since they possess only 2-keto-3-deoxygluconate-6-phosphate aldolase.

     

Aromatic amino acid biosynthesis in Alcaligenes eutrophus H16

1. Mutants derived from the hydrogen bacterium Alcaligenes eutrophus strain H16 auxotrophic for phenylalanine and tyrosine were isolated employing mutagenic agents (EMS, nitrite), the colistine counterselection technique and the “pin-point” isolation method. Three different types of mutants were found: (1) Mutants, requiring phenylalanine or phenylpyruvate for growth, were affected in chorismate mutase as well as prephenate dehydratase. Both activities were regained by reversion to prototrophy. The auxotrophic strains accumulated chorismic acid. (2) Strains with a growth response similar to that of the first group lacked only prephenate dehydratase activity which was partially regained by reversion. Chorismate mutase and prephenate dehydrogenase were derepressed up to two-fold. Mutants grown in minimal medium excreted prephenic acid. (3) The third type of mutants required phenylalanine or phenylpyruvate and grew slowly when supplemented with chorismate or prephenate. The enzymes involved in the specific pathway of phenylalanine and tyrosine were found to be present. Some of them were even more active than in the wild-type.
2. Mutants accumulating chorismic acid or prephenic acid were able to grow on minimal medium when incubated long enough. The chemical instability of the excretion products resulted in their nonenzymatic conversion to subsequent intermediates which were taken up by the cells, allowing growth.
3. A method is described for preparing barium prephenate using the auxotrophic mutant 6B-1 derived from A. eutrophus H16. Prephenic acid, excreted by this strain, was obtained from the culture filtrate with a purity of at least 70% and a yield of approximately 180 mg per 2 l of medium.

     

Effects of high dietary methionine on activities of selected enzymes in the liver of kittens (felis domesticus)

• 1.1. Growing male kittens were fed an 18% casein diet supplemented with 2, 3, or 4% l-methionine (MET) for 6 weeks.
• 2.2. Free MET concentration in liver increased 30-fold and cystathionine two- to three-fold; the activity of adenosyl-MET transferase and cystathionase also increased but remained lower than previously found in rats.
• 3.3. Taurine concentration in liver decreased in cats fed excess MET and appeared to depend on taurine intake.
• 4.4. Alanine aminotransferase activity was high in all groups while serine dehydratase activity was very low.
• 5.5. Pyruvate kinase and malic enzyme activities which are normally low in cat liver increased after excess MET. Also, glucose 6-phosphate and 6-phosphogluconate dehydrogenases increased.
• 6.6. Cat liver metabolism showed limited adaptation to an excess dietary intake of methionine compared to that found in rats.

     

Cyclodextrin-Glucanotransferase von Klebsiella pneumoniae

1. When growing with cyclodextrins, Klebsiella pneumoniae M 5 al produces extracellular cyclodextrin glucanotransferase in amounts comparable to those obtained during the growth with potato starch.
2. Intracellular cyclodextrin glucanotransferase-activity was demonstrated to be present in the homogenates of cells grown with cyclodextrins. In addition, an amylomaltase-like enzyme and the maltodextrin phosphorylase could be pointed out. The cyclodextrins are metabolized to glucose-1-phosphate and glucose by the concerted actions of these three enzymes. paraGlucose-1-phosphate is liberated from cyclohexaamylose by the actions of purified cyclodextrin glucanotransferase and purified maltodextrin phosphorylase. The liberation of the sugar phosphate is increased fivefold by addition of glucose as an acceptor. This sugar, however, retards the formation of glucose-1-phosphate from the cyclic compound by the enzymes of the cell extract: In the presence of glucose the amylomaltase is incapable of synthesizing substrates for the phosphorylase from maltose. This experimental result clearly demonstrates that the amylomaltase is involved in the disproportionation of maltosaccharides arising from the cyclodextrins.
3. A NADP⁺-specific glucose dehydrogenase was demonstrated to be present in the cell extracts. This enzyme, which is activated by ADP, may control the energy-depending pool of free glucose. Glucose originates from the disproportionation of maltosaccharides catalyzed by the glucanotransferases.
4. A glucose-1-phosphate-hydrolysing phosphatase, which is shown to be present in the cell extract, seems to be without physiological significance for the metabolism of the cyclodextrins.
5. Preliminary permeation studies make it probable that the cyclodextrins are transported into the cells as such and degraded only within the cells.
6. A scheme for the metabolism of cyclodextrins in Klebsiella pneumoniae M 5 al is proposed.

     

Light-induced effects of several enzymes of carbohydrate metabolism in Phycomyces blakesleeanus

• 1.1. The photoregulation shown by glyceraldehyde 3-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase appears to be independent of the mad gene product(s) and also independent of carotene biosynthesis regulation.
• 2.2. The photoregulation of malate dehydrogenase appeared to be dependent on the mutation of the mad and car S genes.
• 3.3. Pyruvate kinase and lactate dehydrogenase may be classified as light-independent.
• 4.4. The action of ATP and fructose 1,6-bisphosphate on the enzymes studied was generally independent of light/dark grown conditions.
• 5.5. However, the effect of fructose 1,6-bisphosphate on Phycomyces pyruvate kinase appears to be light-dependent.

     

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

1. With fumarate as the terminal electron acceptor and either H₂ or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.
2. Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.
3. Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.
4. In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.
5. During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H₂ or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO₂.
6. The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H₂ or formate were not detected in the bacterium.

     

Metabolism of the anaerobic formation of succinic acid bySaccharomyces cerevisiae

1. Succinic acid is formed in amounts of 0.2–1.7 g/l by fermenting yeasts of the genusSaccharomyces during the exponential growth phase. No differences were observed between the various species, respiratory deficient mutants and wild type strains.
2. At low glucose concentrations the formation of succinic acid depended on the amount of sugar fermented. However, the nitrogen source was found to be of greater importance than the carbon source.
3. Of all nitrogen sources, glutamate yielded the highest amounts of succinic acid. Glutamate led to an oxidative and aspartate to a reductive formation of succinic acid.
4. A reductive formation of succinic acid by the citric acid cycle enzymes was observed with malate. This was partially inhibited by malonate. No evidence was obtained that the glyoxylate cycle is involved in succinic acid formation by yeasts.
5. Anaerobically grown cells ofSaccharomyces cerevisiae contained α-ketoglutarate dehydrogenase. Its activity was found in the 175000 x g sediment after fractionated centrifugation. The specific activity increased 6-fold after growth on glutamate as compared with cells grown on ammonium sulfate.
6. The specific activities of malate dehydrogenase, fumarase, succinate dehydrogenase, succinylcoenzymeA synthetase, α-ketoglutarate dehydrogenase and glutamate dehydrogenase (nicotinamide adenine dinucleotide dependent) were determined in yeast cells grown on glutamate or ammonium sulfate. Similar results were obtained with a wild type strain and a respiratory deficient mutant. The latter did not contain succinate dehydrogenase.
7. In fermenting yeasts succinic acid is mainly formed from glutamate by oxidation.

     

Effect of cyclic amp on suncus murinus liver serine-aminotransferase and serine dehydratase

• 1.1. Suncus murinus was injected dibutyryl adenosine 3′,5′-cyclic monophosphate (Bt₂cAMP) and assayed serine-glyoxylate aminotransferase (EC 2.6.1.45) and serine dehydratase (EC 4.2.1.13).
• 2.2. Serine dehydratase was induced 4-fold by Bt₂cAMP. The K_m values of the induced enzyme for l-serine and pyridoxal 5′-phosphate was 57 mM and 3.0 μM, respectively. The enzyme had a pH optimum at pH 10.0. These kinetic properties and pH optimum were same as those of the enzyme from the control. Both the holoenzyme and the apoenzyme increased to the same extent by Bt₂cAMP.
• 3.3. Serine-glyoxyate aminotransferase activity was decreased slightly by the Bt₂cAMP injection. The holoenzyme activity was increased, but the apoenzyme decreased. K_m values for l-serine and glyoxylate of this enzyme were 6mM and 0.2 mM, respectively, without change by Bt₂cAMP.

     

The salt relations of marine and halophilic species of the unicellular green alga,Dunaliella

1. Comparisons were made of the effects of salt on the exponential growth rates of two unicellular algae,Dunaliella tertiolecta (marine) andDunaliella viridis (halophilic).
2. The algae contained glycerol in amounts which varied directly with the salt concentration of the growth media. The highest measured glycerol content ofD. tertiolecta was approximately equivalent to 1.4 molal and occurred in algae grown in 1.36 M sodium chloride. The highest glycerol content measured inD. viridis was approximately equivalent to 4.4 molal and occurred in algae grown in 4.25 M sodium chloride. Lower concentrations of free glucose, which varied inversely with extracellular salt concentration, were also detected.
3. It is inferred that Na⁺ is effectively excluded from the two algae. There was some evidence of a moderate uptake of K⁺.
4. Comparisons were made of erude preparations of the glucose-6-phosphate dehydrogenase and an NADP-specific glycerol dehydrogenase from each species and of the effects of salt and glycerol on the activities of these enzymes. It is concluded that the different salt tolerances of the two algae cannot be explained by generalized differences between their enzyme proteins.
5. Although intracellular glycerol must necessarily contribute to the osmotic status of the algae, its primary function in influencing their salt relations is considered to be that of a compatible solute, whereby glycerol maintains enzyme activity under conditions of high extracellular salt concentration and hence low (thermodynamic) water activity.

     

2-Deoxyglucose transport by the frog sartorius: Effects of electrical stimulation and N-carbobenzoxy-glycyl-l-phenylalaninamide

• 1.1. Studies characterizing glucose transport in the frog sartorius were performed.
• 2.2. For nonstimulated and stimulated muscles, intracellular 2-deoxyglucose exceeded 2-deoxyglucose-6-phosphate at 15 min, showed little further increase, and was maintained below the extracellular concentration for 2 hr.
• 3.3. Accumulated 2-deoxyglucose-6-phosphate did not inhibit glucose transport.
• 4.4. Unlike in adipocytes, basal and stimulated 2-deoxyglucose transport showed no difference in sensitivity to N-carbobenzoxy-glycyl-l-phenylalaninamide.
• 5.5. Phenylarsine oxide blocked contraction-enhanced 2-deoxyglucose uptake.
• 6.6. These results suggest that the glucose transporter of the sartorius exhibits auto-regulation, and that basal transport is not regulated by the same process as in adipocytes.

     

Pathway for D-galactonate catabolism in nonpathogenic mycobacteria.

D-Galactonate is catabolized in saprophytic mycobacteria to give pyruvate and glyceraldehyde-3-phosphate by a pathway that involves the sequential reactions of galactonate dehydratase, 2-keto-3-deoxy-galactonate kinase, and 6-phospho-2-keto-3-deoxy-galactonate aldolase.     

Content and synthesis of several abundant glycolytic enzymes in skeletal muscles of normal and dystrophic mice

• 1.1. In both 2- and 3-month-old 129 ReJ mice, the catalytic activity levels of three enzymes involved in glycogen breakdown (phosphorylase, enolase, and aldolase) were found to be 35–50% lower in hind limb muscles of dystrophic mice as compared with normal mice.
• 2.2. The reduced activities of these enzymes in the diseased tissue was directly due to corresponcling reductions in the number of enzyme molecules rather than being due to inactivation of the enzymes in the dystrophic muscle.
• 3.3. Results of short term double isotope incorporation experiments conducted with muscle expiants in vitro suggested that the rates of synthesis of these enzymes, and of most other abundant cytosolic proteins, relative to each other, were similar in hind limb muscles of normal and dystrophic mice.
• 4.4. The present work on murine muscular dystrophy is discussed in terms of our previous studies into the influence of avian muscular dystrophy on the content and synthesis of abundant glycolytic enzymes in chicken skeletal muscles.

     

Intracellular localization and characterization of 3-hydroxykynureninase in human liver

• 1.1. 3-hydroxykynureninase in human liver was present in cytosol and mitoehondria.
• 2.2. The cytosolic enzyme and mitochondrial enzyme had the same physiological and enzymic properties.
• 3.3. The enzyme had a mol. wt of 130,000 by gel filtration and isoelectric point of pH 5.9.
• 4.4. The enzyme was active for 3-hydroxykynurenine and kynurenine, and its activity ratio was 15:1. The apparent K_m values of the enzyme were 7.7 × 10⁻⁵M for 3-hydroxykynurenine, 1.0×10⁻³M for kynurenine and 2.5 × 10⁻⁶M for pyridoxal 5'-phosphate with 3-hydroxykynurenine.
• 5.5. Some other properties of purified enzymes are described.

     

Studies on the enzymatic activities related to varied pattern of diets in the air-breathing cat fish,clarias batrachus (Linn.)

1. Specific activity of amylase, cellulase, protease and lipase in the intestines of the air-breathing catfish, Clarias batrachus (Linn.) has been studied.
2. Excepting amylase and protease, the activity of lipase and cellulase showed practically no changes with change in the nutritional status of the diets.
3. pH optima of all enzymes were between 6.9 and 7.6
4. There is reason to believe from cellulase and high amylase activity in the intestine of the species that its culture operation could be done more economically by giving them a supplementary diet from indigeneously available raw material particularly from plant origin.

     

d-Xylose Degradation Pathway in the Halophilic Archaeon Haloferax volcanii

The pathway of d-xylose degradation in archaea is unknown. In a previous study we identified in Haloarcula marismortui the first enzyme of xylose degradation, an inducible xylose dehydrogenase (Johnsen, U., and Schönheit, P. (2004) J. Bacteriol. 186, 6198–6207). Here we report a comprehensive study of the complete d-xylose degradation pathway in the halophilic archaeon Haloferax volcanii. The analyses include the following: (i) identification of the degradation pathway in vivo following ¹³C-labeling patterns of proteinogenic amino acids after growth on [¹³C]xylose; (ii) identification of xylose-induced genes by DNA microarray experiments; (iii) characterization of enzymes; and (iv) construction of in-frame deletion mutants and their functional analyses in growth experiments. Together, the data indicate that d-xylose is oxidized exclusively to the tricarboxylic acid cycle intermediate α-ketoglutarate, involving d-xylose dehydrogenase (HVO_B0028), a novel xylonate dehydratase (HVO_B0038A), 2-keto-3-deoxyxylonate dehydratase (HVO_B0027), and α-ketoglutarate semialdehyde dehydrogenase (HVO_B0039). The functional involvement of these enzymes in xylose degradation was proven by growth studies of the corresponding in-frame deletion mutants, which all lost the ability to grow on d-xylose, but growth on glucose was not significantly affected. This is the first report of an archaeal d-xylose degradation pathway that differs from the classical d-xylose pathway in most bacteria involving the formation of xylulose 5-phosphate as an intermediate. However, the pathway shows similarities to proposed oxidative pentose degradation pathways to α-ketoglutarate in few bacteria, e.g. Azospirillum brasilense and Caulobacter crescentus, and in the archaeon Sulfolobus solfataricus.d-Xylose, a constituent of the polymer xylan, is the major component of the hemicellulose plant cell wall material and thus one of the most abundant carbohydrates in nature. The utilization of d-xylose by microorganisms has been described in detail in bacteria and fungi, for which two different catabolic pathways have been reported. In many bacteria, such as Escherichia coli, Bacillus, and Lactobacillus species, xylose is converted by the activities of xylose isomerase and xylulose kinase to xylulose 5-phosphate as an intermediate, which is further degraded mainly by the pentose phosphate cycle or phosphoketolase pathway. Most fungi convert xylose to xylulose 5-phosphate via xylose reductase, xylitol dehydrogenase, and xylulose kinase. Xylulose 5-phosphate is also an intermediate of the most common l-arabinose degradation pathway in bacteria, e.g. of E. coli, via activities of isomerase, kinase, and epimerase (1).Recently, by genetic evidence, a third pathway of xylose degradation was proposed for the bacterium Caulobacter crescentus, in analogy to an alternative catabolic pathway of l-arabinose, reported for some bacteria, including species of Azospirillum, Pseudomonas, Rhizobium, Burkholderia, and Herbasprillum (2, 3). In these organisms l-arabinose is oxidatively degraded to α-ketoglutarate, an intermediate of the tricarboxylic acid cycle, via the activities of l-arabinose dehydrogenase, l-arabinolactonase, and two successive dehydration reactions forming 2-keto-3-deoxy-l-arabinoate and α-ketoglutarate semialdehyde; the latter compound is further oxidized to α-ketoglutarate via NADP⁺-specific α-ketoglutarate semialdehyde dehydrogenase (KGSADH).² In a few Pseudomonas and Rhizobium species, a variant of this l-arabinose pathway was described involving aldolase cleavage of the intermediate 2-keto-3-deoxy-l-arabinoate to pyruvate and glycolaldehyde, rather than its dehydration and oxidation to α-ketoglutarate (4). Because of the presence of some analogous enzyme activities in xylose-grown cells of Azosprillum and Rhizobium, the oxidative pathway and its variant was also proposed as a catabolic pathway for d-xylose. Recent genetic analysis of Caulobacter crecentus indicates the presence of an oxidative pathway for d-xylose degradation to α-ketoglutarate. All genes encoding xylose dehydrogenase and putative lactonase, xylonate dehydratase, 2-keto-3-deoxylonate dehydratase, and KGSADH were found to be located on a xylose-inducible operon (5). With exception of xylose dehydrogenase, which has been partially characterized, the other postulated enzymes of the pathway have not been biochemically analyzed.The pathway of d-xylose degradation in the domain of archaea has not been studied so far. First analyses with the halophilic archaeon Haloarcula marismortui indicate that the initial step of d-xylose degradation involves a xylose-inducible xylose dehydrogenase (6) suggesting an oxidative pathway of xylose degradation to α-ketoglutarate, or to pyruvate and glycolaldehyde, in analogy to the proposed oxidative bacterial pentose degradation pathways. Recently, a detailed study of d-arabinose catabolism in the thermoacidophilic crenarchaeon Sulfolobus solfataricus was reported. d-Arabinose was found to be oxidized to α-ketoglutarate involving d-arabinose dehydrogenase, d-arabinoate dehydratase, 2-keto-3-deoxy-d-arabinoate dehydratase, and α-ketoglutarate semialdehyde dehydrogenase (3).In this study, we present a comprehensive analysis of the complete d-xylose degradation pathway in the halophilic archaeon Haloferax volcanii. This halophilic archaeon was chosen because it exerts several suitable properties for the analyses. For example, it can be cultivated on synthetic media with sugars, e.g. xylose, an advantage for in vivo labeling studies in growing cultures. Furthermore, a shotgun DNA microarray of H. volcanii is available (7) allowing the identification of xylose-inducible genes, and H. volcanii is one of the few archaea for which an efficient protocol was recently described to generate in-frame deletion mutants.Accordingly, the d-xylose degradation pathway was elucidated following in vivo labeling experiments with [¹³C]xylose, DNA microarray analyses, and the characterization of enzymes involved and their encoding genes. The functional involvement of genes and enzymes was proven by constructing corresponding in-frame deletion mutants and their analysis by selective growth experiments on xylose versus glucose. The data show that d-xylose was exclusively degraded to α-ketoglutarate involving xylose dehydrogenase, a novel xylonate dehydratase, 2-keto-3-deoxyxylonate dehydratase, and α-ketoglutarate semialdehyde dehydrogenase.     

The regulation of glucose 6-phosphate dehydrogenase from Dicentrarchus labrax (bass) liver

• 1.1. Kinetic constant values of the reaction catalyzed by bass liver glucose 6-phosphate dehydrogenase show to be modified between 10 and 40°C.
• 2.2. The Arrhenius plot between 10 and 50°C shows two slopes with different activation energies.
• 3.3. These results suggest a regulation of this enzyme by environmental temperature.
• 4.4. Kinetics of ATP inhibition were examined between pH 6.2 and 7.8: patterns and K_i values obtained are affected by the pH variation.
• 5.5. NADH is an effective inhibitor of bass glucose 6-phosphate dehydrogenase but this enzyme does not show NAD-linked activity.
• 6.6. Kinetics of pyridoxal 5′-phosphate inhibition have indicated the presence of a lysine in the catalytic site for NADP⁺.

     

Cytologische Untersuchungen an strahleninduzierten Mutanten vonBrassica oleracea var.capitata

The meiosis of two mutants ofBrassica oleracea var.capitata was analysed which have been isolated after gamma irradiation and hybridization.

1. Univalents appear in different frequencies in the pollen mother cells of both these mutants attributed to a genetically conditioned reduction of the chiasmata frequency resulting in manifold irregularities in the later stages of microsporogenesis. The number of microspores per PMC varies between 1 and 8, the chromosome number of the microspores between 6 and 12. As a consequence of these meiotic disturbances a strong reduction of the fertility of male and female germ cells occurs.
2. In principle, both mutants show the same meiotic behaviour, but the irregularities appear in a stronger degree in mutant 45 as compared with mutant 47. They are obviously caused by the same mutated gene which shows differences in its manifestation in the two mutants due to their different genotypic constitution.
3. The mutant gene belongs to the group of desynaptic genes controlling the process of chiasmata formation. The degree of desynapsis caused by this gene is very weak as compared with ds-genes of other species.

     

Studies on intestinal protease: Isolation,purification and effect of dietary proteins on alkaline protease activity of the air-breathing fish,Clarias batrachus (Linn.)

1. The effect of dietary protein levels on the proteolytic activity in the intestines of the air-breathing fish, Clarias batrachus (Linn.) has been studied
2. Activity of proteolytic enzymes increased significantly in fishes maintained with a 50% protein diet from those maintained with a 25% protein diet; still higher dietary protein percentage showed no further stimulation of enzyme activity.
3. In a study on the determination of sub-cellular localisation, it has been found that protease activity is more prominent in lysosomes than in other organelles of the cell.
4. A sixty fold purification of alkaline protease from the intestine of Clarias batrachus has been achieved by ion exchange chromatography on DEAE cellulose which has been further checked by polyacrylamide gel electrophoresis.

     

The Nonphosphorylative Entner-Doudoroff Pathway in the Thermoacidophilic Euryarchaeon Picrophilus torridus Involves a Novel 2-Keto-3-Deoxygluconate- Specific Aldolase

The pathway of glucose degradation in the thermoacidophilic euryarchaeon Picrophilus torridus has been studied by in vivo labeling experiments and enzyme analyses. After growth of P. torridus in the presence of [1-¹³C]- and [3-¹³C]glucose, the label was found only in the C-1 and C-3 positions, respectively, of the proteinogenic amino acid alanine, indicating the exclusive operation of an Entner-Doudoroff (ED)-type pathway in vivo. Cell extracts of P. torridus contained all enzyme activities of a nonphosphorylative ED pathway, which were not induced by glucose. Two key enzymes, gluconate dehydratase (GAD) and a novel 2-keto-3-deoxygluconate (KDG)-specific aldolase (KDGA), were characterized. GAD is a homooctamer of 44-kDa subunits, encoded by Pto0485. KDG aldolase, KDGA, is a homotetramer of 32-kDa subunits. This enzyme was highly specific for KDG with up to 2,000-fold-higher catalytic efficiency compared to 2-keto-3-deoxy-6-phosphogluconate (KDPG) and thus differs from the bifunctional KDG/KDPG aldolase, KD(P)GA of crenarchaea catalyzing the conversion of both KDG and KDPG with a preference for KDPG. The KDGA-encoding gene, kdgA, was identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) as Pto1279, and the correct translation start codon, an ATG 24 bp upstream of the annotated start codon of Pto1279, was determined by N-terminal amino acid analysis. The kdgA gene was functionally overexpressed in Escherichia coli. Phylogenetic analysis revealed that KDGA is only distantly related to KD(P)GA, both enzymes forming separate families within the dihydrodipicolinate synthase superfamily. From the data we conclude that P. torridus degrades glucose via a strictly nonphosphorylative ED pathway with a novel KDG-specific aldolase, thus excluding the operation of the branched ED pathway involving a bifunctional KD(P)GA as a key enzyme.Comparative analyses of sugar-degrading pathways in members of the domain Archaea revealed that all species analyzed so far degrade glucose and glucose polymers to pyruvate via modification of the classical Embden-Meyerhof (EM) and Entner-Doudoroff (ED) pathways found in bacteria and eukarya. Modified EM pathways were reported for hyperthermophilic archaea, including, e.g., the strictly fermentative Thermococcales and Desulfurococcales, the sulfur-reducing Thermoproteus tenax, and the microaerophilic Pyrobaculum aerophilum. These pathways differ from the classical EM pathway by the presence of several novel enzymes and enzyme families, catalyzing, e.g., the phosphorylation of glucose and fructose-6-phosphate, isomerization of glucose-6-phosphate, and oxidation of glyceraldehyde-3-phosphate (18, 22, 25).Modified ED pathways have been proposed for aerobic archaea, including halophiles, and thermoacidophilic crenarchaea, such as Sulfolobus species, and the euryarchaea Thermoplasma acidophilum and Picrophilus torridus. The anaerobic Thermoproteus tenax, which degrades glucose predominantly via a modified EM pathway, also utilizes—to a minor extent (<20%)—a modified ED pathway for glucose degradation. The following ED pathway modifications have been reported in archaea (25). A semiphosphorylative ED pathway was reported in halophilic archaea. Accordingly, glucose is converted to 2-keto-3-deoxy-6-gluconate (KDG) via glucose dehydrogenase and gluconate dehydratase. KDG is then phosphorylated by KDG kinase to 2-keto-3-deoxy-6-phosphogluconate (KDPG), which is split by KDPG aldolase to pyruvate and glyceraldehyde-3-phosphate (GAP). GAP is further converted to form another pyruvate via common reactions of the EM pathway, i.e., phosphorylative GAP dehydrogenase, phosphoglycerate kinase, phosphoglycerate mutase, enolase, and pyruvate kinase. The net ATP yield of this pathway is 1 ATP/mol glucose.From initial enzyme studies of the thermoacidophilic archaea Sulfolobus solfataricus, Thermoplasma acidophilum, and Thermoproteus tenax, a nonphosphorylative ED pathway was proposed (25). In this modification of the ED pathway, glucose is converted to KDG via glucose dehydrogenase and gluconate dehydratase, as in the semiphosphorylative pathway, but then the steps differ as follows: KDG is cleaved into pyruvate and glyceraldehyde via 2-keto-3-deoxygluconate-specific aldolase (KDGA). The subsequent oxidation of glyceraldehyde to glycerate involves either NAD(P)⁺-dependent dehydrogenases or oxidoreductases. Glycerate is then phosphorylated by a specific kinase to 2-phosphoglycerate, which is finally converted to pyruvate via enolase and pyruvate kinase. This modification of the ED pathway was called “nonphosphorylative” since it is not coupled with net ATP synthesis.However, recent comparative genomic studies and refined enzyme analyses suggest that the crenarchaea Sulfolobus and Thermoproteus utilize a so-called branched ED pathway, in which a semiphosphorylated route is simultaneously operative in addition to the nonphosphorylative route (25, 32). Accordingly, the semiphosphorylated route involves—via KDG kinase—the phosphorylation of KDG to KDPG, which is then cleaved to pyruvate and GAP by means of a bifunctional KDG/KDPG aldolase, KD(P)GA. GAP is then converted to another pyruvate via nonphosphorylative GAP dehydrogenase (GAPN), phosphoglycerate mutase, enolase, and pyruvate kinase. The net ATP yield of the branched ED pathway is zero. In support of this pathway, the genes encoding gluconate dehydratase, bifunctional KD(P)GA, KDG kinase, and GAPN were found to be clustered in Sulfolobus solfataricus (see Discussion) and Thermoproteus tenax. The key enzyme of the proposed branched ED pathway is the bifunctional KD(P)GA, which catalyzes the cleavage of KDG to pyruvate and glyceraldehyde and cleavage of KDPG to pyruvate and glyceraldehyde-3-phosphate. This bifunctional aldolase, which has been characterized from S. solfataricus, was found to be identical to a previously described KDG aldolase of the same organism; however, its catalytic property to also utilize KDPG as a substrate has been recognized only recently. In fact, the bifunctional KD(P)GA showed a higher catalytic efficiency for KDPG than for KDG (1, 14). Crystal structures of bifunctional KD(P)GAs of S. solfataricus and T. tenax have been reported (16, 27, 30; G. Taylor [United Kingdom], unpublished data).The branched ED pathway in S. solfataricus has been reported to be promiscuous and therefore represents an equivalent degradation route for both glucose and its C-4 epimer, galactose. Accordingly, glucose dehydrogenase, gluconate dehydratase, KDG kinase, and bifunctional KD(P)GA were found to catalyze the conversion of both glucose and galactose and the corresponding subsequent intermediates, i.e., gluconate/galactonate, KDG/KDGal (KDGal stands for 2-keto-3-deoxygalactonate), and KDPG/KDPGal (KDPGal stands for 2-keto-3-deoxy-6-phosphogalactonate) (4, 12-14).In contrast to crenarchaea, the modified ED pathway in the thermoacidophilic euryarchaea Thermoplasma acidophilum and Picrophilus torridus has not been studied in detail. Enzyme measurements in cell extracts and the characterization of few enzymes suggest the operation of a nonphosphorylative ED pathway in these organisms (2, 3, 17, 19, 25). However, in vivo evidence for the operation of an ED-type pathway, e.g., by ¹³C-labeling experiments with growing cultures, has not been provided yet. Furthermore, the KDG aldolase activity measured in cell extracts of P. torridus and T. acidophilum has not been purified and characterized, in particular with respect to substrate specificity, and the genes encoding these enzymes have not been identified. The biochemical analysis of this aldolase is crucial to define the enzyme as a KDG-specific aldolase, indicative of a nonphosphorylative ED pathway, or as bifunctional KD(P)GA, indicative of the branched ED pathway as proposed for the crenarchaea Sulfolobus and Thermoproteus.In this communication we studied the sugar-degrading pathway in P. torridus by in vivo labeling experiments with [¹³C]glucose, by enzyme measurements, and by characterization of two key enzymes, gluconate dehydratase and KDG aldolase. The data indicate that P. torridus utilizes a strict nonphosphorylative ED pathway, involving a novel KDG-specific aldolase as a key enzyme, and thus exclude the operation of a branched ED pathway, as in crenarchaea involving a bifunctional KD(P)GA as a key enzyme.     

Growth of a floating aquatic weed,Salvinia under standard conditions

1. Growth of the floating aquatic weed, Salvinia, in sterile culture was exponential for at least 2 weeks under standardized conditions.
2. Increase in light intensity or in CO₂ resulted in increases in growth rate, but did not extend the exponential period of growth.
3. This aquatic plant, like many others, discriminates against calcium relative to strontium.
4. In culture Salvinia exhibited luxury consumption of N and P.
5. Because of high C/N ratios, Salvinia may not be a favorable source of animal food, but might be useful in nutrient removal schemes.
6. In sterile culture, S. molesta produced fewer leaves than S. minima, but maintained a significant increase in leaf area and dry weight. This may be correlated with the ability of the first species to rapidly spread over tropical waterways.