Maternal effect for genes encoding 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase in Drosophila melanogaster

We studied the maternal effect for two enzymes of the pentose cycle, 6-phosphogluconate dehydrogenase (6PGD) and glucose-6-phosphate dehydrogenase (G6PD), using a genetic system based on the interaction of Pgd^? and Zw^? alleles, which inactivate 6PGD and G6PD, respectively. The presence and formation of the enzymes was investigated in those individuals that had not received the corresponding genes from the mother. We revealed maternal forms of the enzymes, detectable up to the pupal stage. The activities of “maternal” 6PGD and G6PD per individual increased 20-fold to 30-fold from the egg stage to the 3rd larval instar even in the absence of normal Pgd and Zw genes. Immunologic studies have shown that the increase in 6PGD activity is due to an accumulation of the maternal form of the enzyme molecules. We revealed a hybrid isozyme resulting from an aggregation of the subunits of isozymes controlled by the genes of the mother and embryo itself. These results indicate that the maternal effect in the case of 6PGD is due to a long-lived stable mRNA transmitted with the egg cytoplasm and translated during the development of Drosophila melanogaster.     

Purification and characterization of the molybdoenzymes nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase from Bacillus niacini

The enzymes nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase from Bacillus niacini could be purified to homogeneity by means of anion exchange chromatography, hydrophobic interaction chromatography, gel filtration, and chromatography on hydroxylapatite. During enrichment procedures both enzymes showed a significant loss in specific activity. The molecular weight of nicotinate dehydrogenase and 6-hydroxynicotinate dehydrogenase was determined to be about 300,000 and 120,000, respectively. They were highly substrate specific and transferred electrons only to artificial acceptors of high redox potential. The K _m for their specific substrates was about 1.0 mM for both enzymes, and their pH optimum was determined to be 7.5. For nicotinate dehydrogenase a content of 8.3 mol iron, 1.5 mol acid-labile sulfur, 2.0 mol flavin, and 1.5 mol molybdenum per mol of enzyme was determined. Both enzymes contained FAD and Fe/S center. After inhibition by KCN, thiocyanate was detected, and subsequently the initial nicotinate dehydrogenase activity was restored by the addition of Na₂S indicating the presence of cyanolyzable sulfur. 6-Hydroxynicotinate dehydrogenase seemed to contain the same type of constituents as determined for nicotinate dehydrogenase. A partial immunological identity of the enzymes could be shown by antibodies raised against nicotinate dehydrogenase.Abbreviations DCPIP 2,6-dichlorophenol-indophenol - EEO electroendosmosis - FTTC fluorescein isothiocyanate - HAP hydroxylapatite - 6-HDH 6-hydroxynicotinate dehydrogenase - NBT nitroblue tetrazolium chloride - NDH nicotinate dehydrogenase - MTT thiazolyl blue - PES phenazine ethosulfate - PMSF phenylmethyl sulfonyl fluoride - TEMED N,N,N',N'-tetramethyl-ethylenediamine     

Inhibition of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in sea urchin eggs by palmitoyl-coenzyme a and reversal by polyamines

Palmitoyl-CoA inhibited crude glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in the eggs of the sea urchin, Hemicentrotus pulcherrimus. Fifty percent inhibition of the glucose 6-phosphate dehydrogenase in the supernatant of unfertilized eggs was obtained with 0.43 ± 0.05 μm palmitoyl-CoA, and of 6-phosphogluconate dehydrogenase with 4.41 ± 0.20 μm palmitoyl-CoA. Also, these enzymes in fertilized eggs 30 min after fertilization were inhibited by palmitoyl-CoA almost as much as in unfertilized eggs. Na-Palmitate, coenzyme A, acetyl-CoA, palmitoylcarnitine, and carnitine failed to exert any inhibitory effect on the activities of these dehydrogenases. The intracellular concentration of long-chain fatty acyl-CoA in unfertilized eggs (3.08 ± 0.33 nmol/10⁶ eggs) was high enough for the inhibition of these enzymes, and decreased following fertilization to a low level (1.49 ± 0.08 nmol/10⁶ eggs 30 min after fertilization). Spermine and spermidine canceled the inhibition of these enzymes by palmitoyl-CoA. In view of the inhibition of glucose 6-phosphate dehydrogenase and of 6-phosphogluconate dehydrogenase by palmitoyl-CoA, these dehydrogenases in the pentose monophosphate cycle are probably inhibited in unfertilized eggs by long-chain fatty acyl-CoA and released from the inhibited state by both the decrease in the level of long-chain acyl-CoA and the increase in the level of polyamines following fertilization.     

Glucose-6-phosphate dehydrogenase of Anabaena sp.

The kinetic and molecular properties of cyanobacterial glucose-6-phosphate dehydrogenase, partly purified from Anabaena sp. ATCC 27893, show that it undergoes relatively slow, reversible transitions between different aggregation states which differ in catalytic activity. Sucrose gradient centrifugation and polyacrylamide gel electrophoresis reveal three principal forms, with approximate molecular weights of 120 000 (M ₁), 240 000 (M ₂) and 345 000 (M ₃). The relative catalytic activities are: M ₁M ₂<M ₃. In concentrated solutions of the enzyme, the equilibrium favors the more active, oligomeric forms. Dilution in the absence of effectors shifts the equilibrium in favor of the M ₁ form, with a marked diminution of catalytic activity. This transition is prevented by a substrate, glucose-6-phosphate, and also by glutamine. The other substrate, nicotinamide adenine dinucleotide phosphate (NADP⁺), and (in crude cell-free extracts) ribulose-1,5-diphosphate are negative effectors, which tend to maintain the enzyme in the M ₁ form. The equilibrium state between different forms of the enzyme is also strongly dependent on hydrogen ion concentration. Although the optimal pH for catalytic activity is 7.4, dissociation to the hypoactive M ₁ form is favored at pH values above 7; a pH of 6.5 is optimal for maintenace of the enzyme in the active state. Reduced nicotamide adenine dinucleotide phosphate (NADPH) and adenosine 5-triphosphate (ATP), inhibit catalytic activity, but do not significantly affect the equilibrium state. The relevance of these findings to the regulation of enzyme activity in vivo is discussed.Abbreviations G6PD glucose-6-phosphate dehydrogenase - 6PGD 6-phosphogluconate dehydrogenase - RUDP ribulose-1,5-diphosphate - G6P glucose-6-phosphate - 6PG 6-phosphogluconate     

Glutamate dehydrogenase activity in developing soybean seed: Isolation and characterization of three forms of the enzyme

Three forms of glutamate dehydrogenase have been isolated from developing soybean seed. Their intracellular locations could not be determined directly because organelles and marker enzymes showed abnormal distribution on sucrose density gradient fractionation. By analogy with enzymes from other parts of the plant, glutamate dehydrogenase 2 was shown to be located in chloroplasts and glutamate dehydrogenase 3 in mitochondria. Glutamate dehydrogenase 1 could not be located in this way because it is found only in the seed. The three enzymes are similar in pH optima, molecular weight and substrate specificity with respect to 2-oxoglutarate and l-glutamate. The mitochondrial enzyme is specific for NAD⁺. The chloroplast enzyme shows low activity with NADP⁺ relative to NAD⁺ but uses NADPH readily in the aminating direction. Glutamate dehydrogenase 1 is active with both nucleotides and is the only form to show substantial deaminating activity with NADP⁺. Glutamate dehydrogenases 1 and 2 are activated and stabilized by glutathione and 2-mercaptoethanol whereas enzyme 3 is unaffected. No significant metabolic control of any of the enzymes could be detected. Malate, citrate, adenine nucleotides and long-chain fatty acyl CoA derivatives gave slight inhibition at high concentrations. Amino acids had no effect on activity. A possible role for the enzyme characteristic of the developing seed is discussed in relation to nutrient supply during the accumulation of reserve materials in the seed.     

The influence of temperature on glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and the regulation of these enzymes in a mesophilic and a thermophilic cyanobacterium

The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K _m's are for G6PDH: 80M (substrate) and 20M (NADP⁺); for 6PGDH: 90M (substrate) and 25M (NADP⁺). In Synechococcus 6716 the apparent K _m's are for G6PDH: 550M (substrate) and 30M (NADP⁺); for 6PGDH: 40M (substrate) and 10M (NADP⁺). None of the K _m's is influenced by the growth temperature and only the K _m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine     

Glyoxysomal malate dehydrogenase of watermelon cotyledons: De novo synthesis on cytoplasmic ribosomes

The development of glyoxysomal malate dehydrogenase (gMDH, EC 1.1.1.37) during early germination of watermelon seedlings (Citrullus vulgaris Schrad.) was determined in the cotyledons by means of radial immunodiffusion. The active isoenzyme was found to be absent in dry seeds. By density labelling with deuterium oxide and incorporation of [¹⁴C] amino acids it was shown that the marked increase of gMDH activity in the cotyledons during the first 4 days of germination was due to de novo synthesis of the isoenzyme. The effects of protein synthesis inhibitors (cycloheximide and chloramphenicol) on the synthesis of gMDH indicated that the glyoxysomal isoenzyme was synthesized on cytoplasmic ribosomes. Possible mechanisms by which the glyoxysomal malate dehydrogenase isoenzyme reaches its final location in the cell are discussed.Abbreviations mMDH mitochondrial malate dehydrogenase - gMDH glyoxysomal malate dehydrogenase - D₂O deuterium oxide - EDTA ethylenediaminetetraacetic acid, disodium salt     

Effect of astaxanthin and aluminum chloride on erythrocyte G6PD and 6PGD enzyme activities in vivo and on erythrocyte G6PD in vitro in rats

In this study, we investigated the effect of astaxanthin (Ast) and aluminum (Al) on the erythrocyte glucose‐6‐phosphate dehydrogenase (G6PD) and 6‐phosphogluconate dehydrogenase (6PGD) enzymes activities in vivo and on G6PD enzyme in vitro in rats. For in vitro studies, G6PD enzyme was purified from rat erythrocyte by using 2′,5′‐ADP‐Sepharose 4B affinity gel. The effects of Ast and Al³⁺ ion were investigated on the purified enzyme. It was determined that Ast increased the enzyme activity, whereas Al³⁺ inhibited the enzyme activity noncompetitively (IC₅₀ values; 0.679 mM, K_i values 1.32 mM). For in vivo studies, the rats were divided into the groups: control (Cont.), Al, Ast, and Al + Ast. The last three groups were compared with the control group. In Al group, a significant degree of inhibition was observed in the activity of G6PD and 6PGD enzymes when compared with the control group (P < 0.05), whereas there was an increase in the activities of G6PD and 6PGD enzymes in Ast and Al + Ast groups (P < 0.05).     

Primate red cell enzymes: glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase

Glucose-6-phosphate dehydrogenase (E. C.: 1.1.1.49) phenotypes and 6-phosphogluconate dehydrogenase (E. C.: 1.1.1.44) phenotypes were determined by starch-gel electrophoresis of red cell hemolysates of Galago crassicaudatus subspp., Propithecus verreauxi, Lemur spp., Hapalemur griseus, and Macaca mulatta. A single glucose-6-phosphate dehydrogenase (G6PD) phenotype was found in each species. A single 6-phosphogluconate dehydrogenase (6PGD) phenotype was found in Lemur spp., Hapalemur griseus, and Galago crassicaudatus argentatus. In a group of six Propithecus verreauxi, three 6PGD phenotypes, PGD A, PGD AB, and PGD B, were found. Three phenotypes, PGD A, PGD AB, and PGD B, were found in 38 G. c. crassicaudatus. The three phenotypes in each species are apparently the products of two codominant autosomal alleles, PGD^A and PGD^B. The frequency of PGD^A in G. c. crassicaudatus is 0.263. A population of 260 free-ranging macaques displays a polymorphism at the 6PGD locus. Three phenotypes, PGD A, PGD AB, and PGD B, were found. These also appear to be controlled by two codominant autosomal alleles, PGD^A and PGD^B the frequency of PGD^A = 0.913. Additional analysis of three well-defined troops within the macaque population indicated that there are no significant differences between the troops or within the population at the 6PGD locus.     

Insulin-like effects of vanadate and selenate on the expression of glucose-6-phosphate dehydrogenase and fatty acid synthase in diabetic rats

Isulin is capable of regulating cellular and metabolic processes as well as gene expression. In recent years, enthusiasm has surfaced for using insulin mimetics to study the mechanism of action of insulin. Vanadata and selenate are two compounds that have been found to mimic the action of insulin on control to blood glucose levels in vivo. Vanadata has also been shown to regulate the expression of several enzymes both in vivo, however, studies concerning selenate's ability to regulate expression have not been reported. In his study we show that administration of vanadate or selenate to streptozotocin-induced diabetic rats not only normalizes blood glucose levels similarly to insulin but also positively affects the expression of two key metabolic enzymes, glucose-6-phosphate dehydrogenase (G6PDH) and fatty acid synthase (FAS). Both G6PDH and FAS activity are significantly decreased in diabetic animals compared to non-diabetic control. Treatment of the diabetic animals with either insulin, vanadate or selenate restored both activities to about 80–90% of control. All treatment conditions exhibited activities significantly higher than those determined for the diabetic group but did not differ significantly from each other. Increases in GPDH or FAS activity are due to increases in mRNA level. Increase in both G6PDH and FAS mRNA was comparable to the observed increase in activity suggesting that regulation of expression by the mimetics occurs pretranslationally.     

Glucose-6-phosphate dehydrogenase in barley roots: kinetic properties and localisation of the isoforms

Two different isoforms of glucose-6-phosphate dehydrogenase (Glc6PDH; EC 1.1.1.49) have been partially purified from barley (Hordeum vulgare L., cv. Alfeo) roots. The procedure included an ammonium sulfate step, Q-Sepharose and Reactive Blue agarose chromatography, and led to 60-fold and 150-fold purification for the two enzymes, respectively. The Glc6PDH 1 isoform accounts for 17% of total activity of the enzyme in roots, and is very sensitive to the effects of NADP⁺/NADPH ratio and dithiothreitol; the Glc6PDH 2 isoform is less affected by reducing power and represents 83% of the total activity. The isoforms showed distinct pH optima, isoelectric points, K _m for glucose-6-phosphate and a different electrophoretic mobility. The kinetic properties for the two enzymes were affected by ATP and metabolites. Both enzymes are inhibited to different extents by ATP when magnesium is omitted from the assay mixture, whereas the addition of ATP-Mg²⁺ had no effect on Glc6PDH activities. The Glc6PDH isoforms are usually present in the plastids and cytosol of plant cells. To verify the intracellular locations of the enzymes purified from barley roots, Glc6PDH was purified from isolated barley root plastids; this isoform showed kinetic parameters coincident with those found for Glc6PDH 1, suggesting a plastid location; the enzyme purified from the soluble fraction had kinetic parameters resembling those of Glc6PDH 2, confirming that this isoform is present in the cytosol of barley roots. Received: 21 June 2000 / Accepted: 28 July 2000     

The increase in activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in skeletal muscles of rats after subcutaneous administration of N,N′-dimethyl-para-phenylenediamine

Summary After subcutaneous administration of N,N-dimethyl-para-phenylenediamine (DPPD) in rats, a myogenic myopathy was produced in the skeletal muscles. In this communication, the results of the application of various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases and biochemical techniques for the estimation of activities of oxidoreductases in the experimental skeletal muscles are presented. The most striking result was the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase which increased dramatically during the early phase of the muscle disease. The increase in activity of the pentose phosphate shunt enzymes was the first pathological alteration and was present as early as 8 h after a single injection of DPPD. Histochemical techniques for demonstration of activity of both enzymes are therefore highly suited for the detection of minor diseases and the early onset of major diseases of the neuromuscular system. Some glycolytic enzymes as well as some enzymes of the aerobic part of the metabolism showed an early decrease or increase in activity indicating a metabolic imbalance in the muscle fibres. There were more fibres with an intermediate pattern of the energy yielding enzymes in the experimental muscle specimens then in specimens from the control groups. The activity of the catabolic hydrolytic enzymes was strongly increased in pathological muscles. The aerobic muscles were more vulnerable to DPPD than the anaerobic muscles.     

Effetto di Inibitori Della Sintesi Proteica Sull'aumento di Attività Enzimatiche e sul Risveglio del Metabolismo Nell'Endosperma di Semi di Ricino in Germinazione

Abstract

Effects of inhibitors of protein synthesis on the development of metabolic activity in the endosperm during the germination of castor bean seeds. — The effect of chloramphenicol, streptomycin and actinomycin-C on the increase of the activities of glyceroaldehyde-phosphate dehydrogenase, aldolase, glucose-6-phosphate dehydrogenase, fructose 1–6 diphosphate-1-phosphatase, phosphomonoesterase, in the endosperm of germinating castor bean seeds was investigated.

In all cases, the protein synthesis inhibitors depressed the activation of the enzymes tested: in particular, actinomycin (50 μg/ml) completely suppressed the increase of the activities.

The development of the rate of oxygen uptake and the conversion of fats to sugars was strongly affected by the inhibitors.

These data suggest that the increase of the activities of several enzymes in the germinating endosperm is dependent on enzyme synthesis rather than on the conversion from the inactive to the active form of the enzymes.     

Hexose metabolism in pancreatic islets: Succinate dehydrogenase activity in islet homogenates

Succinate dehydrogenase activity was measured in rat pancreatic islet homogenates incubated in the presence of [1,4-¹⁴C]succinate, the reaction velocity being judged through the generation of ¹⁴CO₂ in the auxiliary reactions catalysed by pig heart fumarase and chicken liver NADP-malate dehydrogenase. In the presence of 1·0 mM succinate, the reaction velocity averaged 5·53 ± 0·44 pmol min^?1 μg^?1 islet protein. The K_m for succinate was close to 0·4 mM and the enzymic activity was restricted to mitochondria. These kinetic results indicate that, under the present experimental conditions, the activity of succinate dehydrogenase does not vastly exceed that of either NAD-isocitrate dehydrogenase or the 2-ketoglutarate dehydrogenase complex, at least when the latter enzymes are activated by ADP and/or Ca²⁺. Nevertheless, the activity of succinate dehydrogenase is sufficient to account for the increase in O₂ uptake evoked in intact islets by the monomethyl ester of succinic acid. It could become a rate-limiting step of the Krebs cycle in models of B-cell dysfunction.     

Cooperativity between 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase in the lumen of the endoplasmic reticulum

The functional coupling of 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase was investigated in rat liver microsomal vesicles. The activity of both enzymes was latent in intact vesicles, indicating the intraluminal localization of their active sites. Glucose-6-phosphate, a substrate for hexose-6-phosphate dehydrogenase, stimulated the cortisone reductase activity of 11beta-hydroxysteroid dehydrogenase type 1. Inhibition of glucose-6-phosphate uptake by S3483, a specific inhibitor of the microsomal glucose-6-phosphate transporter, decreased this effect. Similarly, cortisone increased the intravesicular accumulation of radioactivity upon the addition of radiolabeled glucose-6-phosphate, indicating the stimulation of hexose-6-phosphate dehydrogenase activity. A correlation was shown between glucose-6-phosphate-dependent cortisone reduction and cortisone-dependent glucose-6-phosphate oxidation. The results demonstrate a close cooperation of the enzymes based on co-localization and the mutual generation of cofactors for each other.     

Histochemical localization of primary and secondary alcohol dehydrogenases in whole-body, freeze-dried sections of mice

Summary Whole-body sagittal sections of frozen, C57BL/6J, adult, male mice were used for the localization of primary and secondary alcohol dehydrogenases in most tissues of the body. The reduction of Nitro BT with NAD⁺ as coenzyme, as described originally by Hardonk (1965), was utilized for the generation of coloured final reaction deposits. Ethanol was used as a substrate for primary alcohol dehydrogenase; 2-propanol, -methylbenzyl alcohol and 2-butanol were used as substrates for secondary alcohol dehydrogenase. Liver and bronchial epithelium showed the highest activities for both enzymes; oesophageal and upper gastric epithelium showed a high activity of primary alcohol dehydrogenase. Pyrazole, indazole and imidazole inhibited primary, but not secondary, alcohol dehydrogenase. Dimethylsulphoxide and menthol slightly inhibited both enzymes. Oleic acid, sulphydryl agents,p-chloromercuribenzoate, and copper sulphate also inhibited both enzymes. Slight inhibition of secondary dehydrogenase was observed on co-administration of several alcohols.As expected,N-nitrosonornicotine did not function as a substrate for alcohol dehydrogenases. When this compound was present in the histochemical incubation media, no activity was seen at any of the usual sites of these enzymes. The distribution of the alcohol dehydrogenase activities found in this study correlates with the distribution of radioactivity in oesophagus, bronchi and liver after administration of [¹⁴C]nitrosonornicotine. This suggests that the alcohol dehydrogenases may be involved in the metabolism of hydroxylated nitrosonornicotine, a metabolite of the most abundant known carcinogen in cigarette smoke.     

6-Phosphogluconate dehydrogenase in cell free extracts of Escherichia coli K-12

Summary Investigations into the properties of 6-PG dehydrogenase in cell free extracts of Escherichia coli revealed a pH optimum at pH 9.5 with a sharp decline on both sides of the optimum. The addition of 1.0×10^-2 m MgCl₂ produced maximal activity, whereas higher concentrations caused inhibition. The K _m values were 2.5×10^-4 m for 6-phosphogluconate and 2.5×10^-5 m for NADP⁺ as substrate. The enzyme was extremely stable for at least 5 hours if stored at 4°C in Tris–NaCl–MgCl₂ buffer at pH 7.5. 6-PG dehydrogenase activity was shown to be proportional to cell free extract concentration over the range 0–0.3 mg protein. An assay method based on the new optimal conditions has been established and has been shown to be 33% more sensitive than a number of commonly used methods.Meinem hochverehrten Lehrer Herrn Professor A. Rippel zum 80. Geburtstage.     

Glucose-6-phosphate dehydrogenase in cell free extracts of Zymomonas mobilis

Summary Glucose-6-phosphate dehydrogenase activity in cell free extracts o Zymomonas mobilis showed marked differences when compared with the corresponding enzyme of Escherichia coli. It exhibited 3 times higher activity and the reaction rate over 10 min gave linearity only up to a cell free protein concentration of 0.15 mg protein. This different behaviour was not a function of environmental growth conditions of the culture nor of the nine different assay methods employed. A constant relationship existed between the specific G-6-P dehydrogenase protein and the total protein concentration in the cell free extract. The enzyme was stable for at least 5 h at 4°C in Tris-NaCl-MgCl₂-buffer.An investigation of the properties of G-6-P dehydrogenase from Z. mobilis revealed a pH optimum of 8.7 with a rapid decline towards the acidic and a small decrease towards the alkaline side. The K _m values were 5×10^-4 m for glucose-6-phosphate and 3.6×10^-5 m NADP⁺. The addition of 1×10^-2 m MgCl₂ produced optimal activity but higher concentrations inhibited the enzyme reaction.These results were discussed with those from other sources and found to be unique for Zymomonas mobilis.Meinem hochverehrten Lehrer Herrn Professor A. Rippel zum 80. Geburtstage.     

Exopolysaccharide Production and Peculiarities of C6-Metabolism in Acinetobacter sp. Grown on Carbohydrate Substrates

An Acinetobacter sp. strain grown on carbohydrate substrates (mono- and disaccharides, molasses, starch) was shown to synthesize exopolysaccharides (EPS). Glucose catabolism proved to proceed via the Embden–Meyerhof–Parnas and Entner–Doudoroff pathways. Pyruvate entered the tricarboxylic acid cycle due to pyruvate dehydrogenase activity. Pyruvate carboxylation by pyruvate carboxylase was the anaplerotic reaction providing for the synthesis of intermediates for the constructive metabolism of Acinetobacter sp. grown on C₆-substrates. The C₆-metabolism in Acinetobacter sp. was limited by coenzyme A. Irrespective of the carbohydrate growth substrate (glucose, ethanol), the activities of the key enzymes of both C₂- and C₆-metabolism was high, except for the isocitrate lyase activity in glucose-grown bacteria. Isocitrate lyase activity was induced by C₂-compounds (ethanol or acetate). After their addition to glucose-containing medium, both substrates were utilized simultaneously, and an increase was observed in the EPS synthesis, as well as in the EPS yield relative to biomass. The mechanisms responsible for enhancing the EPS synthesis in Acinetobacter sp. grown on a mixture of C₂- and C₆-substrates are discussed.