A fast spheroplast formation procedure in some 2,5-diketo-D-gluconate- and 2-keto-L-gulonate- producing bacteria

Calcium 2-keto-L-gulonate (Ca-2-KLG, a key intermediate in vitamin C synthesis) is produced from calcium 2,5-diketo D-gluconate (Ca-2,5-DKG) by a variety of bacteria. A few bacterial species which efficiently convert glucose to Ca-2,5-DKG have been isolated in our laboratory. Our bacterial collection included species that possess the genes for production of Ca-2-KLG from Ca-2,5-DKG; however, the yield of the former is poor. A procedure for the preparation of spheroplasts in Ca-2,5-DKG- and Ca-2-KLG-producing bacteria was developed for the construction of recombinants (fusants), combining the genes for conversion of glucose to Ca-2-KLG efficiently by protoplast fusion. The standard procedure for spheroplast formation in Gram negative bacteria by the Tris-sucrose-EDTA-lysozyme system did not work in the organisms under investigation. The need for an alternative method was necessary. Our results show that, while the Tris-NaCl-EDTA-lysozyme system (pH 8.3) worked very well with bacterial strains of Gluconobacter oxydans (ATCC9937) and Acetobacter melanogenus (NCIM2259), the Tris-sucrose-EDTA-lysozyme system worked well for Erwinia herbicola (ATCC21998), Pseudomonas chlororaphis (NCIM2041) and Corynebacterium species (ATCC31090). However, none of these systems produced spheroplasts in Brevibacterium ketosoreductum (ATCC21914), for which a separate system is under development.

Inhibition of biopterin synthesis and DOPA production in PC-12 pheochromocytoma cells induced by 6-aminonicotinamide

Pheochromocytoma cells (clone PC-12) were treated with 6-aminonicotinamide. Tetrahydrobiopterin content and DOPA production of the cells were determined by reverse-phase HPLC and subsequent electrochemical detection. The same chromatographic system was used to determine total biopterin (tetrahydrobiopterin, dihydrobiopterin and quinoide dihydrobiopterin) by fluorescence detection. Tetrahydrobiopterin plays a decisive role as cofactor of tyrosine hydroxylase for the biosynthesis of DOPA and dopamine. Addition of 6-aminonicotinamide to the culture medium resulted in the accumulation of 6-phosphogluconate, suggesting that PC-12 cells synthesize 6-aminonicotinamide-adenine-dinucleotide-phosphate (6-ANADP) by a glycohydrolase localized in the endoplasmic reticulum. This substance is known to be a strong inhibitor of 6-phosphogluconate dehydrogenase and leads to a blockade of the pentose phosphate pathway. In our experiments, the synthesis of biopterins was depressed after application of 6-aminonicotinamide. The decrease of intracellular tetrahydrobiopterin and total biopterin by 6-aminonicotinamide at different concentrations was strongly correlated with a reduced cellular DOPA production. The decreased content of biopterin cofactor was compensated by addition of the precursor sepiapterin, indicating that the NADPH2-dependent reductases in biopterin synthesis are not inhibited by the antimetabolite. However, DOPA production remained suppressed at the same time. After application of NADH2, we observed an increased DOPA production though the decreased biopterin levels remained almost unchanged. The results imply that the first step in the synthesis of biopterin from GTP as well as the recycling pathways of the oxidized cofactor might be the site of action of the antimetabolite.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of an operator sequence for the Bacillus subtilis gnt operon

Expression of the Bacillus subtilis gluconate (gnt) operon is negatively regulated by the gnt repressor which is antagonized by D-gluconate or D-glucono-delta-lactone. The repressor specifically binds to a gnt operator near the gnt promoter. From the results of gel retardation assaying of the gnt repressor and various restriction enzyme digests of a fragment carrying the gnt promoter and the gntR gene, the gnt operator was found to be located within a 141-base pair region containing the gnt promoter. Deoxyribonuclease I protection experiments revealed that the gnt repressor protected a gnt promoter region, between -10 and +15, which contains a region showing dyad symmetry with a sequence showing half-symmetry, ATACTTGTA. A 35-base pair synthetic duplex DNA containing this region showing dyad symmetry specifically bound to the gnt repressor. Through cleavage at two AccI sites in the protected region an 8-base pair deletion was introduced into the region showing dyad symmetry, which made expression of the gnt promoter constitutive. A DNA fragment carrying this deletion did not bind to the repressor. These results clearly indicated that the gnt operator sequence is a sequence containing the region showing dyad symmetry located at the transcription initiation site of the gnt operon. It was also suggested that the gnt operon contains only one operator. The similarity in the recognition between the repressor-operator interaction of the gnt operon and those of Escherichia coli TrpR and its operators was discussed.

Selection of glucose-assimilating variants of Acinetobacter calcoaceticus LMD 79.41 in chemostat culture

Glucose metabolism has been studied in two strains of Acinetobacter calcoaceticus. Strain LMD 82.3, was able to grow on glucose and possessed glucose dehydrogenase (EC 1.1.99.17). Glucose oxidation by whole cells was stimulated by PQQ, the prosthetic group of glucose dehydrogenase. PQQ not only increased the rate of glucose oxidation and gluconic acid production but also shortened the lag phase for growth on glucose. Strain LMD 79.41 also possessed glucose dehydrogenase but was unable to grow on glucose. Batch cultures and carbon-limited chemostat cultures growing on acetate in the presence of glucose oxidized the sugar to gluconic acid, which was not further metabolized. However, after prolonged cultivation on mixtures of acetate and glucose, carbon-limited chemostat cultures suddenly acquired the capacity to utilize gluconate. This phenomenon was accompanied by the appearance of gluconate kinase and a repression of isocitrate lyase synthesis. In contrast to the starter culture, cells from chemostats which had been fully adapted to gluconate utilization, were able to utilize glucose as a sole carbon and energy source in liquid and solid media.

Intracellular pH during "chemical hypoxia" in cultured rat hepatocytes. Protection by intracellular acidosis against the onset of cell death

The relationships between extracellular pH (pHo), intracellular pH (pHi), and loss of cell viability were evaluated in cultured rat hepatocytes after ATP depletion by metabolic inhibition with KCN and iodoacetate (chemical hypoxia). pHi was measured in single cells by ratio imaging of 2',7'-biscarboxy-ethyl-5,6-carboxyfluorescein (BCECF) fluorescence using multiparameter digitized video microscopy. During chemical hypoxia at pHo of 7.4, pHi decreased from 7.36 to 6.33 within 10 min. pHi remained at 6.1-6.5 for 30-40 min (plateau phase). Thereafter, pHi began to rise and cell death ensued within minutes, as evidenced by nuclear staining with propidium iodide and coincident leakage of BCECF from the cytoplasm. An acidic pHo produced a slightly greater drop in pHi, prolonged the plateau phase of intracellular acidosis, and delayed the onset of cell death. Inhibition of Na+/H+ exchange also prolonged the plateau phase and delayed cell death. In contrast, monensin or substitution of gluconate for Cl- in buffer containing HCO3- abolished the pH gradient across the plasma membrane and shortened cell survival. The results indicate that intracellular acidosis after ATP depletion delays the onset of cell death, whereas reduction of the degree of acidosis accelerates cell killing. We conclude that intracellular acidosis protects against hepatocellular death from ATP depletion, a phenomenon that may represent a protective adaptation against hypoxic and ischemic stress.

Kinetic studies of Haemophilus influenzae 6-phosphogluconate dehydrogenase

Haemophilus influenzae 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate:NADP+ 2-oxidoreductase (decarboxylating), EC 1.1.1.44) was purified 308-fold to electrophoretic homogeneity with a 16% recovery through a five-step procedure involving salt fractionation and hydrophobic and affinity chromatography. The purified enzyme was demonstrated to be a dimer of Mr 70,000, and to catalyze a sequential reaction process. The enzyme was NADP-specific and kinetic parameters for the oxidation of 6-phosphogluconate were determined for NADP and four structural analogs of NADP. Coenzyme-competitive inhibition by adenosine derivatives was significantly enhanced by the presence of a 2'-phosphoryl group consistent with the observed coenzyme specificity of the enzyme. The purified enzyme was effectively inhibited by 3-aminopyridine adenine dinucleotide phosphate, but at concentrations higher than that observed to inhibit growth of the organism. Rates of inactivation of the enzyme by N-ethylmaleimide were suggestive of sulfhydryl involvement in the reaction catalyzed.

Characteristics of histidine uptake by human placental microvillous membrane vesicles

L-histidine is an essential amino acid. Its fetal-to-maternal blood concentration ratio is high, suggesting active placental transport. In this study, human placental microvillous membrane vesicles were used to characterize L-histidine transport, heretofore not evaluated in human tissue. L-Histidine uptake by microvillous membrane vesicles was stimulated by an inward sodium gradient, leading to an "overshoot," followed by apparent equilibration. Linear uptake at 22 degrees C was limited to the 1st min. The initial sodium-dependent uptake rate was proportional to the sodium concentration in the medium. The sodium-dependent uptake was markedly diminished or lost when potassium, cesium, or choline was substituted for sodium but not lithium. Replacement of chloride with sulfate or gluconate had little effect. Sodium-stimulated L-histidine uptake was further stimulated by an outward potassium gradient (inside-negative) in the presence of valinomycin. Sodium-dependent uptake kinetic constants for L-histidine were: Km = 0.44 +/- 0.18 mM: Vmax = 536 +/- 94 nmol/mg/30 s (mean +/- SD). 2-(methylamino)isobutyric acid did not inhibit L-histidine uptake. Conversely, L-histidine noncompetitively inhibited sodium-dependent uptake of 2-(methylamino)isobutyric acid and L-cysteine. L-glutamine competitively inhibited sodium-dependent L-histidine uptake. L-histidine uptake was stimulated by preloading the vesicles with either L-histidine or L-glutamine (transstimulation). L-histidine uptake was not sensitive to N-ethylmaleimide treatment but was strongly inhibited by low pH. These findings suggest that L-histidine is transported in the human placenta by a specific sodium-dependent system similar to the "N" system described in rodent hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Fitness effects of a deletion mutation increasing transcription of the 6-phosphogluconate dehydrogenase gene in Escherichia coli

Directed evolution in microbial organisms provides an experimental approach to molecular evolution in which selective forces can be controlled and favorable mutations analyzed at the molecular level. Here we present an analysis of a mutation selected in Escherichia coli in response to growth in a chemostat in which the limiting nutrient was gluconate. The selectively favored mutation, designated gnd+ (862), occurred in the gene gnd coding for 6-phosphogluconate dehydrogenase, used in gluconate metabolism. Although the allele is strongly favored in chemostats in which the limiting nutrient is gluconate, the selective effects of gnd+ (862) are highly dependent on growth conditions. In chemostats in which growth is limited by a mixture of gluconate and either ribose, glucose, or succinate, the gnd+ (862) allele is favored, disfavored, or neutral according to the relative concentrations of the substrates. The gnd+ (862) allele results from a deletion of 385 nucleotide pairs in the region 5' to the promoter of gnd, and one endpoint of the deletion is contiguous with the terminus of an IS5 insertion sequence located near gnd in E. coli K12. The gnd+ (862) allele shows a marked increase in transcription that accounts for most or all of the increased enzyme activity.

Channels at the catalytic site of glycogen phosphorylase b: binding and kinetic studies with the beta-glycosidase inhibitor D-gluconohydroximo-1,5-lactone N-phenylurethane

Regions of low packing density in the vicinity of the catalytic site of glycogen phosphorylase b are described with the aid of a computer program that generates a contour map in which the contour level is inversely proportional to the packing density in the protein. It is shown that, although there is no direct route from the catalytic site to the surface, there are two possible channels that could allow access for substrates following conformational changes in the enzyme. The first channel, channel 1, leads from the catalytic site to the surface close to the nucleoside inhibitor site and requires movements of residues 280-285 and Arg 569 in order to obtain access. Previous crystallographic experiments have shown that in the presence of substrates or R-state inhibitors these parts of the polypeptide chain undergo large conformational changes. The properties of the second channel (channel 2), which is the more extensive channel, have been investigated with the potent beta-glycosidase inhibitor D-gluconohydroximo-1,5-lactone N-phenylurethane (PUG). Crystallographic binding studies at 2.4-A resolution show that the compound binds neatly at the catalytic site of phosphorylase b. The glucopyranosylidene ring, in the half-chair conformation, occupies a similar but not identical position (shift about 0.6 A) to that occupied by other glucosyl compounds bound at the catalytic site.(ABSTRACT TRUNCATED AT 250 WORDS)

Taurine and cell volume maintenance in the shark rectal gland: cellular fluxes and kinetics

Tissue slices of shark rectal gland are studied to examine the kinetics of the cellular fluxes of taurine, a major intracellular osmolyte in this organ. Maintenance of high steady-state cell taurine (50 mM) is achieved by a ouabain-sensitive active Na+-dependent uptake process and a relatively slow efflux. Uptake kinetics are described by two saturable taurine transport components (high-affinity, Km 60 microM; and low-affinity, Km 9 mM). [14C]Taurine uptake is enhanced by external Cl-, inhibited by beta-alanine and unaffected by inhibitors of the Na+/K+/2Cl- co-transport system. Two cellular efflux components of taurine are documented. Incubation of slices in p-chloromercuribenzene sulfonate (1 mM) reduces taurine uptake, increases efflux of taurine and induces cell swelling. Studies of efflux in isotonic media with various cation and anion substitutions demonstrate that high-K+ markedly enhances taurine efflux irrespective of cell volume changes (i.e. membrane stretching is not involved). Moreover, iso-osmotic cell swelling induced in media containing propionate is not associated with enhanced efflux of taurine from the cells. It is suggested that external K+ exerts a specific effect on the cytoplasmic membrane to increase its permeability to taurine.

Apical Na+ permeability of frog skin during serosal Cl- replacement

Gluconate substitution for serosal Cl- reduces the transepithelial short-circuit current (Isc) and depolarizes short-circuited frog skins. These effects could result either from inhibition of basolateral K+ conductance, or from two actions to inhibit both apical Na+ permeability (PapNa) and basolateral pump activity. We have addressed this question by studying whole-and split-thickness frog skins. Intracellular Na+ concentration (CcNa) and PapNa have been monitored by measuring the current-voltage relationship for apical Na+ entry. This analysis was conducted by applying trains of voltage pulses, with pulse durations of 16 to 32 msec. Estimates of PapNa and CcNa were not detectably dependent on pulse duration over the range 16 to 80 msec. Serosal Cl- replacement uniformly depolarized short-circuited tissues. The depolarization was associated with inhibition of Isc across each split skin, but only occasionally across the whole-thickness preparations. This difference may reflect the better ionic exchange between the bulk medium and the extracellular fluid in contact with the basolateral membranes, following removal of the underlying dermis in the split-skin preparations. PapNa was either unchanged or increased, and CcNa either unchanged or reduced after the anionic replacement. These data are incompatible with the concept that serosal Cl- replacement inhibits PapNa and Na,K-pump activity. Gluconate substitution likely reduces cell volume, triggering inhibition of the basolateral K+ channels, consistent with the data and conclusions of S.A. Lewis, A.G. Butt, M.J. Bowler, J.P. Leader and A.D.C. Macknight (J. Membrane Biol. 83:119-137, 1985) for toad bladder. The resulting depolarization reduces the electrical force favoring apical Na+ entry. The volume-conductance coupling serves to conserve volume by reducing K+ solute loss. Its molecular basis remains to be identified.

The kinetics of glucose-fructose oxidoreductase from Zymomonas mobilis

Glucose-fructose oxidoreductase operates by a classic ping-pong mechanism with a single site for all substrates: glucose, fructose, gluconolactone and sorbitol. The Km values for these substrates were determined. The values of kcat are 200 s-1 and 0.8 s-1 for the forward and reverse directions respectively. The overall catalytic process consists of two half-reactions with alternate reduction of NADP+ and oxidation of NADPH tightly bound to the enzyme. Reduction of enzyme-NADP+ by glucose and oxidation of enzyme-NADPH by gluconolactone involve single first-order processes. The values of the rate constants at saturating substrate are 2100 s-1 and 8 s-1 respectively; deuterium isotope effects indicate that these are for the hydrogen transfer step. Oxidation of enzyme-NADPH by fructose is first order with a limiting rate constant of at least 430 s-1. The reaction of enzyme-NADP+ with sorbitol is biphasic, with rate constants for both phases less than 1 s-1. This behaviour is explained by a mechanism in which the slow cyclisation of the acyclic form of fructose follows its dissociation from the enzyme. The rate-determining steps for the overall reaction are probably dissociation of gluconolactone in the forward direction and hydrogen transfer from sorbitol to enzyme-bound NADP+ in the reverse direction.

Hexose monophosphate pathway activity in normal and hypoxic rat brain

Experiments were undertaken to define the role of the alternative route of glucose metabolism in the hexose monophosphate pathway (HMP) during energy balanced, mild brain hypoxia. In similar hypoxic model in spite of the lack of the deficit of high energy compounds, the significant acceleration of glycolysis and inhibition of macromolecular syntheses (lipid, proteins, and nucleic acids) were previously observed. The HMP activity, although directly coupled to intracellular synthetic processes, has not been defined and little is known about the mechanisms of its regulation under brain hypoxia. HMP activity was examined in the rat brain in vivo by estimation of the increment of 6-phosphogluconate concentration after inhibition of its oxidation as achieved by injection of 6-aminonicotinamide. The activity of this alternative route of glucose metabolism was estimated to be 0.4 mmol/h/kg w.w. in the brain cortex and 0.7 mmol/h/kg w.w. in the brain stem. During 2 h of mild hypoxia (7% O2 in N2) the HMP activity dropped to 30% of control level, whereas during first hour of reoxygenation increased to 200% of control. Increased activity of HMP in posthypoxic brain during reoxygenation also was observed in vitro by measuring the rate of [1-14C]- and [6-14C]glucose conversion to 14CO2 in cerebral cortical slices. The possible mechanism of the rapid changes in the activity of HMP induced by hypoxia is discussed. The results suggest that the brain glucose metabolism under mild hypoxia is reoriented toward energy producing pathway (glycolysis) partially at the expense of HMP. The mechanism of this regulation seems not to be directly triggered by energy deficit. Activity of HMP in the brain is in accord with the intracellular synthetic processes and their demands on the metabolites produced by this pathway. Relying upon that, the posthypoxic stimulation of HMP would indicate the metabolic recovery during reoxygenation.

Prophylaxis and treatment of rhinovirus colds with zinc gluconate lozenges

Following a tolerance study, double-blind placebo controlled trials were conducted to determine the prophylactic effect of zinc gluconate lozenges on rhinovirus challenge and, in a third study, their therapeutic efficacy when given at the start of colds caused by virus inoculation was tested. In the prophylaxis study a total of 57 volunteers received lozenges of either zinc gluconate (23 mg) (29 volunteers) or matched placebo (28 volunteers) every 2 h while awake during a period of four and a half days. They were challenged with 10(2) tissue culture infecting dose (TCID50) of human rhinovirus 2 (HRV-2) on the second day of medication, and were monitored daily for symptoms and signs of colds and laboratory evidence of infection. Zinc reduced the total mean clinical score from 8.2 in the placebo group to 5.7 and the reduction of the mean clinical score was statistically significant on the second day after virus challenge. In the therapeutic study 69 volunteers were inoculated with 10(2) TCID50 of HRV-2 and those who developed cold symptoms were randomly allocated to receive either zinc gluconate lozenges (six volunteers) or matched placebo lozenges (six volunteers) every two hours they were awake for six days. Treatment of colds with zinc reduced the mean daily clinical score and this was statistically significant on the fourth and fifth day of medication. Similarly, medication also reduced the mean daily nasal secretion weight and total tissue count and these reductions were statistically significant on days two and six for nasal secretion weights and days four to six of medication for tissue counts when compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion transport in human colon in vitro

Ion transport in the human colon was studied in vitro under short-circuit conditions. The proximal, transverse, and distal colon all actively absorbed Na and Cl at similar rates. Tissue conductance was lower in proximal colon, but there were no other regional differences in basal electrophysiologic parameters. There was a gradient of amiloride-sensitive electrogenic Na transport. Whereas amiloride had only a minimal effect in proximal colon, it inhibited 70% of short-circuit current and 50% of net Na absorption in distal colon. Ion substitution experiments demonstrated an electroneutral, coupled Na-Cl cotransport system in proximal and distal colon. Neither amphotericin nor impermeant anions had a consistent stimulatory effect on short-circuit current in human colon. Theophylline (10(-3) M), increased short-circuit current by 4 microEq X cm-2 X h-1, stimulated net Cl secretion, but did not block net Na absorption. Epinephrine, via an alpha 2-adrenergic mechanism, significantly decreased short-circuit current but did not alter Na or Cl transport. These results suggest that all segments of human colon actively absorb Na and Cl, Na absorption occurs by both electrogenic Na absorption and electroneutral Na-Cl cotransport, there is an aboral gradient of increasing electrogenic Na transport, theophylline stimulates secretion in a pattern most consistent with electrogenic Cl secretion, and epinephrine does not increase Na-Cl cotransport in human distal colon. These studies demonstrate that human colon in vitro has distinct transport properties that must be considered both in clinical situations and in comparison to animal models.

The gluconate operon gnt of Bacillus subtilis encodes its own transcriptional negative regulator

The gluconate (gnt) operon of Bacillus subtilis consists of four gnt genes; the second and third genes code for gluconate kinase (gluconokinase, EC 2.7.1.12) and gluconate permease, respectively. A fragment carrying the promoter of this operon (gnt promoter) and the first gene (gntR) was subcloned into a promoter probe vector (pPL603B). Repression of the expression of cat-86 gene, encoded in the vector portion of a constructed plasmid (pgnt21), that is under the control of the gnt promoter was removed by gluconate. The results of deletion analysis and of insertional inactivation of the gntR gene cloned in pgnt21 suggested that the product of the gntR gene, actually synthesized as a 29-kDa protein in vivo, is involved in repression of the gnt promoter. A 4-base-pair insertional mutation within the gntR gene constructed in vitro was introduced into the B. subtilis chromosomal gnt operon by use of linkage of the 4 base pairs to gntK10 in transformation. The introduced mutation gntR1 caused the constitutive expression of the gluconate kinase and gluconate permease genes. S1 nuclease analysis indicated that the mRNA of this operon is synthesized in the gntR1 strain and amounts of mRNA are not changed very much by gluconate, which acts as an inducer in the wild-type gene. These results strongly indicate that the gntR gene codes for a transcriptional negative regulator for the gnt operon.

Gluconate metabolism in germinated spores of Bacillus megaterium QM B1551: primary roles of gluconokinase and the pentose cycle

The metabolic pathway of gluconate, a major product of glucose metabolism during spore germination, was investigated in Bacillus megaterium QM B1551. Compared to the parent, mutant spores lacking gluconokinase could not metabolize gluconate, whereas the revertant simultaneously restored the enzyme activity and the ability to metabolize it, indicating that gluconokinase was solely responsible for the onset of gluconate metabolism. To identify a further metabolic route for gluconate, we determined 14C yields in acetate and CO2 formed from [14C]gluconate, and found that experimental ratios of 14CO2/[14C]acetate obtained from [2-14C]gluconate and [3,4-14C]gluconate were not compatible with the ratios predicted from the Entner-Doudoroff pathway. In contrast, when CO2 release caused by recycling (approx. 30%) was corrected, the ratios almost agreed with those from the pentose cycle. Comparison of specific radioactivities in acetate also supported the conclusion that gluconate was metabolized via the pentose cycle, subsequently metabolized via the Embden-Meyerhof pathway, and finally degraded to acetate and CO2 without a contribution by the Krebs cycle.

Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans

The comparative absorption of zinc after oral administration of three different complexed forms was studied in 15 healthy human volunteers in a double-blind four-period crossover trial. The individuals were randomly divided into four groups. Each group rotated for four week periods through a random sequence of oral supplementation including: zinc picolinate, zinc citrate, and zinc gluconate (equivalent to 50 mg elemental zinc per day) and placebo. Zinc was measured in hair, urine, erythrocyte and serum before and after each period. At the end of four weeks hair, urine and erythrocyte zinc levels rose significantly (p less than 0.005, p less than 0.001, and p less than 0.001) during zinc picolinate administration. There was no significant change in any of these parameters from zinc gluconate, zinc citrate or placebo administration. There was a small, insignificant rise in serum zinc during zinc picolinate, zinc citrate and placebo supplementation. The results of this study suggest that zinc absorption in humans can be improved by complexing zinc with picolinic acid.

Metabolism via the pentose phosphate pathway in rat pheochromocytoma PC12 cells: effects of nerve growth factor and 6-aminonicotinamide

Exposure of rat pheochromocytoma PC12 cells to 0.1 mM 6-aminonicotinamide (6AN) for 24 hours resulted in a 500-fold increase in 6-phosphogluconate indicating active metabolism of glucose via the oxidative enzymes of the pentose phosphate pathway. Amounts of 6-phosphogluconate that accumulated in 6AN-treated cells at 24 hours were significantly increased by treatment of the cells with nerve growth factor (NGF) (100 ng 7S/ml) suggesting that metabolism of glucose via the pentose pathway at this time was enhanced by NGF. This stimulation of metabolism via the pentose pathway is probably a late response to NGF because initial rates of 6-phosphogluconate accumulation in 6AN-treated cells were the same in the presence and absence of NGF. Moreover, amounts of 14CO2 generated from 1-[14CO2]glucose during the initial six hour incubation period were the same in control and NGF-treated cells. Specific activities of hexose phosphates labeled from 1-[14CO2]glucose were also the same in control and NGF-treated cells. The observation that 6AN inhibited metabolism via the pentose phosphate pathway but failed to inhibit NGF-stimulated neurite outgrowth suggests that NADPH required for lipid biosynthesis accompanying NGF-stimulated neurite outgrowth from PC12 cells can be derived from sources other than, or in addition to, the oxidative enzymes of the pentose phosphate pathway.

2-keto-3-deoxygluconate transport system in Erwinia chrysanthemi

In Erwinia chrysanthemi, the gene kdgT encodes a transport system responsible for the uptake of ketodeoxyuronates. We studied the biochemical properties of this transport system. The bacteria could grow on 2,5-diketo-3-deoxygluconate but not on 2-keto-3-deoxygluconate. The 2-keto-3-deoxygluconate entry reaction displayed saturation kinetics, with an apparent Km of 0.52 mM (at 30 degrees C and pH 7). 5-Keto-4-deoxyuronate and 2,5-diketo-3-deoxygluconate appeared to be competitive inhibitors, with Kis of 0.11 and 0.06 mM, respectively. The 2-keto-3-deoxygluconate permease could mediate the uptake of glucuronate with a low affinity. kdgT was cloned on an R-prime plasmid formed by in vivo complementation of a kdgT mutation of Escherichia coli. After being subcloned, it was mutagenized with a mini-Mu-lac transposable element able to form fusions with the lacZ gene. We introduced a kdgT-lac fusion into the E. chrysanthemi chromosome by marker exchange recombination and studied its regulation. kdgT product synthesis was not induced by external 2-keto-3-deoxygluconate in the wild-type strain but was induced by galacturonate and polygalacturonate. Two types of regulatory mutants able to grow on 2-keto-3-deoxygluconate as the sole carbon source were studied. Mutants of one group had a mutation in the operator region of kdgT; mutants of the other group had a mutation in kdgR, a regulatory gene controlling kdgT expression.

Influence of accompanying anion on intestinal radiocalcium absorption

To assess directly the effect of ionic dissociation on the bioavailability of calcium, we used the double isotope inverse convolution method to compare the absorption of calcium gluconate and calcium pyrrolidone carboxylate, an organic, highly dissociated salt. Two tests were performed at a 2 day interval, using in random sequence either salt as a carrier. Forty-eight subjects of various age and clinical condition were studied. The use of the more dissociated salt consistently and significantly increased fractional absorption in a rather constant ratio. Moreover, it slowed absorption in normal subjects whatever their age, and accelerated it in patients with chronic renal failure or osteoporosis, leading to inferences on the alteration of calcium absorption in these conditions.

[Intestinal absorption of calcium gluconate and oseine-mineral complex: an evaluation by conventional analyses]

Calcium (Ca) preparations are widely used in the treatment of osteoporosis, usually as soluble salts. Tolerance might be improved by prescription of slowly dissolved Ca preparations, since Ca is also absorbed distally, even in the colon. In this regard the use of natural forms of Ca might be advantageous, but natural products cannot be labeled reliably for easy evaluation of their absorption. To study the intestinal absorption of an osseino-mineral complex (Ossopan) in comparison with Ca-gluconate, healthy males were investigated by means of conventional blood and urinary measurements before and after ingestion of either substance containing 1.58 g Ca. All subjects were placed on a standard diet 2 days before and during test day. Ca-gluconate (n = 7) evoked a marked and transient rise in plasma ionized calcium; total plasma calcium and urinary calcium followed a parallel course, while plasma and urinary phosphate decreased. After administration of osseino-mineral complex (n = 6), a slow but sustained elevation of plasma ionized calcium was observed while total calcium remained unchanged when corrected by the plasma proteins. Plasma phosphate and proteins increased, as did urinary phosphate. Comparing the 24-hour urine of the test day with that of the previous day, the rise in calcium excretion was slightly greater in the subjects treated by osseino-mineral complex than in those who were given Ca-gluconate, while phosphate excretion increased in the first group and decreased in the second. It is concluded that the bioavailability of Ca in osseino-mineral complex is as good as, if not better than, that of Ca-gluconate.(ABSTRACT TRUNCATED AT 250 WORDS)

Equilibrium and kinetic studies on the binding of gluconolactone to almond beta-glucosidase in the absence and presence of glucose

The binding of glucono-1,5-lactone (gluconolactone) with almond beta-glucosidase was studied at pH 5.0 and 25 degrees C, in the absence and presence of glucose, by monitoring the enzyme fluorescence as a probe. From the results of fluorometric titration, the dissociation constant Kd and the maximum fluorescence intensity increase (percent) of the enzyme-gluconolactone complex relative to the enzyme alone, delta Fmax, were determined to be 12.7 microM and 14.7%, respectively. From the study of the temperature dependence of Kd, delta G degrees, delta H degrees and delta S degrees for the binding were evaluated to be -6.7 kcal mol-1, -3.5 kcal mol-1, and 10.8 e.u. (cal mol-1 deg-1), respectively, at 25 degrees C. The analysis of the fluorometric titration data in the presence of glucose revealed that these ligands bind competitively to the enzyme, probably at the same site. The results of a stopped-flow kinetic study are consistent with the following two-step mechanism: (formula; see text) which indicates that gluconolactone (L) and the enzyme (E) transiently form a loosely bound complex, ELtr (k-1/k+1 = 4.5 mM), in the first rapid bimolecular association step, and ELtr is converted into a more tightly bound complex EL (k+2 = 94 s-1, k-2 = 0.36 s-1) in the subsequent slow unimolecular process. The fluorescence intensity increase occurs solely in the latter step.