Role of glutamine synthetase in citric acid fermentation byAspergillus niger

The activity of glutamine synthetase fromAspergillus niger was significantly lowered under conditions of citric acid fermentation. The intracellular pH of the organism as determined by bromophenol blue dye distribution and fluorescein diacetate uptake methods was relatively constant between 6•0–6•5, when the pH of the external medium was varied between 2•3–7•0.Aspergillus niger glutamine synthetase was rapidly inactivated under acidic pH conditions and Mn2+ ions partially protected the enzyme against this inactivation. Mn2+-dependent glutamine synthetase activity was higher at acidic pH (6•0) compared to Mg2+-supported activity. While the concentration of Mg2+ required to optimally activate glutamine synthetase at pH 6•0 was very high (≥ 50 mM), Mn2+ was effective at 4 mM. Higher concentrations of Mn2+ were inhibitory. The inhibition of both Mn2+ and Mg2+-dependent reactions by citrate, 2-oxoglutarate and ATP were probably due to their ability to chelate divalent ions rather than as regulatory molecules. This suggestion was supported by the observation that a metal ion chelator, EDTA also produced similar effects. Of the end-products of the pathway, only histidine, carbamyl phosphate, AMP and ADP inhibitedAspergillus niger glutamine synthetase. The inhibitions were more pronounced when Mn2+ was the metal ion activator and greater inhibition was observed at lower pH values. These results permit us to postulate that glutamine synthesis may be markedly inhibited when the fungus is grown under conditions suitable for citric acid production and this block may result in delinking carbon and nitrogen metabolism leading to acidogenesis.

Preparation and thermal stability of trioxalatocobaltates of bivalent metals KM2+ [Co(C2O4)3]·xH2O

Trioxalatocobaltates of bivalent metals KM2+[Co(C2O4)3]·x H2O, with M2+ = Ba, Sr, Ca and Pb, have been prepared, characterized and their thermal behaviour studied. The compounds decompose to yield potassium carbonate, bivalent metal carbonate or oxide and cobalt oxide as final products. The formation of the final products of decomposition is influenced by the surrounding atmosphere. Bivalent metal cobaltites of the types KM2+CoO3 and M2+CoO3—x are not identified among the final products of decomposition. The study brings out the importance of the decomposition mode of the precursor in producing the desired end products.

Queuing Models for Estimating Aircraft Fleet Availability

The availability of a small fleet of aircraft in a flying-base, repair-depot combination is modeled and studied. First, a deterministic flow model relates parameters of interest and represents the state-of-the art in the planning of such systems. Second, a cyclic queue model shows the effect of the principal uncertainties in operation and repair and shows the consequent decrease in the availability of aircraft at the flying-base. Several options such as increasing fleet size, investments in additional repair facilities, or building reliability and maintainability into the individual aircraft during its life-cycle are open for increasing the availability. A life-cycle cost criterion brings out some of these features. Numerical results confirm Rose's prediction that there exists a minimal cost combination of end products and repair-depot capability to achieve a prescribed operational availability.

Image -asparaginases from Mycobacterium tuberculosis strains H37Rv and H37Ra

M. tuberculosis H37Ra possesses two Image -asparaginases while the H37Rv strain possesses only a single enzyme. These enzymes have been purified and their properties studied. The two Image -asparaginases in H37Ra strain differ from each other in pH optima, heat inactivation, Michaelis constant and effects of inhibitors, while one of them resembles the single Image -asparaginase present in the H37Rv strain. Image -Cysteine inhibits both Image -asparaginases in an allosteric manner probably because it is one of the end-products in Image -asparagine metabolism. This is the first time that a qualitative difference has been reported in the enzyme pattern between the avirulent and virulent strains of M. tuberculosis.

H-1, C-13, N-15 assignments of the dimeric regulatory subunit (ilvN) of the E. coli AHAS I

Acetohydroxyacid synthase (AHAS) is an enzyme involved in the biosynthesis of the branched chain amino acids viz, valine, leucine and isoleucine. The activity of this enzyme is regulated through feedback inhibition by the end products of the pathway. Here we report the backbone and side-chain assignments of ilvN, the 22 kDa dimeric regulatory subunit of E. coli AHAS isoenzyme I, in the valine bound form. Detailed analysis of the structure of ilvN and its interactions with the catalytic subunit of E. coli AHAS I will help in understanding the mechanism of activation and regulation of the branched chain amino acid biosynthesis.

Regulation of the activity of mung bean (Phaseolus aureus) glutamine synthetase by amino acids and nucleotides

The activity of glutamine synthetase isolated from the germinated seedlings of Phaseolus aureus was regulated by feedback inhibition by alanine, glycine, histidine, AMP, and ADP. When glutamate was the varied substrate, alanine, histidine, and glycine were partial noncompetitive, competitive, and mixed-type inhibitors, respectively. The type of inhibition by these amino acids was confirmed by fractional inhibition analysis. The adenine nucleotides, AMP and ADP, completely inhibited the enzyme activity and were competitive with respect to ATP. Multiple inhibition analyses revealed the presence of separate and nonexclusive binding sites for the amino acids and mutually exclusive sites for adenine nucleotides. Cumulative inhibition was observed with these end products.

Physical chemistry of the reduction of calcium oxide with aluminium in vacuum

The physical chemistry of "aluminothermic" reduction of calcium oxide in vacuum is analyzed. Basic thermodynamic data required for the analysis have been generated by a variety of experiments. These include activity measurements in liquid AI-Ca alloys and determination of the Gibbs energies of formation of calcium aluminates. These data have been correlated with phase relations in the Ca-AI-0 system at 1373 K. The various stages of reduction, the end products and the corresponding equilibrium partial pressures of calcium have been established from thermodynamic considerations. In principle, the recovery of calcium can be improved by reducing the pressure in the reactor. However,, the cost of a high vacuum system and the enhanced time for reduction needed to achieve higher yields makes such a practice uneconomic. Aluminum contamination of calcium also increases at low pressures. The best compromise is to carry the reduction up to the stage where 3CaO-Al,O, is formed as the product. This corresponds to an equilibrium calcium partial pressure of 31.3 Pa at 1373 K and 91.6 Pa at 1460 K. Calcium can be extracted at this pressure using mechanical pumps in approximately 8 to 15 hr, depending on the size and the fill ratio of the retort and porosity of the charge briquettes.

New insights of superoxide dismutase inhibition of pyrogallol autoxidation

Autoxidation of pyrogallol in alkaline medium is characterized by increases in oxygen consumption, absorbance at 440 nm, and absorbance at 600 nm. The primary products are H2O2 by reduction of O-2 and pyrogallol-ortho-quinone by oxidation of pyrogallol. About 20 % of the consumed oxygen was used for ring opening leading to the bicyclic product, purpurogallin-quinone (PPQ). The absorbance peak at 440 nm representing the quinone end-products increased throughout at a constant rate. Prolonged incubation of pyrogallol in alkali yielded a product with ESR signal. In contrast the absorbance peak at 600 nm increased to a maximum and then declined after oxygen consumption ceased. This represents quinhydrone charge-transfer complexes as similar peak instantly appeared on mixing pyrogallol with benzoquinones, and these were ESR-silent. Superoxide dismutase inhibition of pyrogallol autoxidation spared the substrates, pyrogallol, and oxygen, indicating that an early step is the target. The SOD concentration-dependent extent of decrease in the autoxidation rate remained the same regardless of higher control rates at pyrogallol concentrations above 0.2 mM. This gave the clue that SOD is catalyzing a reaction that annuls the forward electron transfer step that produces superoxide and pyrogallol-semiquinone, both oxygen radicals. By dismutating these oxygen radicals, an action it is known for, SOD can reverse autoxidation, echoing the reported proposal of superoxide:semiquinone oxidoreductase activity for SOD. The following insights emerged out of these studies. The end-product of pyrogallol autoxidation is PPQ, and not purpurogallin. The quinone products instantly form quinhydrone complexes. These decompose into undefined humic acid-like complexes as late products after cessation of oxygen consumption. SOD catalyzes reversal of autoxidation manifesting as its inhibition. SOD saves catechols from autoxidation and extends their bioavailability.

Energy-savvy solid-state and sonochemical synthesis of lithium sodium titanate as an anode active material for Li-ion batteries

Lithium sodium titanate insertion-type anode has been synthesized by classical solid-state (dry) and an alternate solution-assisted (wet) sonochemical synthesis routes. Successful synthesis of the target compound has been realized using simple Na- and Li-hydroxide salts along with titania. In contrast to the previous reports, these energy-savvy synthesis routes can yield the final product by calcination at 650 -750 degrees C for limited duration of 1-10 h. Owing to the restricted calcination duration (dry route for 1-2 h and wet route for 1-5 h), they yield homogeneous nanoscale lithium sodium titanate particles. Sono-chemical synthesis reduces the lithium sodium titanate particle size down to 80-100 nm vis-a-vis solid-state method delivering larger (200-500 nm) particles. Independent of the synthetic methods, the end products deliver reversible electrochemical performance with reversible capacity exceeding 80 mAh.g(-1) acting as a 1.3 V anode for Li-ion batteries. (C) 2015 Elsevier B.V. All rights reserved.

Microbial susceptibility of condensation products of carboxy-terminated polybutadiene and glycerol

Keeping in view the prospects of biodegradable polymers, a polymer was synthesized by the condensation of carboxy-terminated polybutadiene (CTPB) of Mnsim-5000 with glycerol and tested for its microbial susceptibility. The results of end group estimations and viscosity measurements indicated a quantitative reaction between the two reactants under experimental conditions. The clear-zone method was employed in this investigation to test biodegradability. Two strains of Serratia and three strains of Staphylococcus did show a clear zone surrounding the colony. However, the microbial growth was found to diminish after 4 or 5 days.

Synthetic studies toward the PPAP natural products, prolifenones A and B and hyperforin: an Effenberger cyclization approach

A synthetic approach toward the geranylated PPAP natural products, prolifenones A and B. employing Effenberger cyclization as the key step, is delineated. The efficacy of this approach is further expanded through access to an advanced precursor of hyperforin. (C) 2010 Elsevier Ltd. All rights reserved.

Sesbania Mosaic Virus (SeMV) Infectious Clone: Possible Mechanism of 3 ` and 5 ` End Repair and Role of Polyprotein Processing in Viral Replication

Sesbania mosaic virus (SeMV) is a positive stranded RNA virus belonging to the genus Sobemovirus. Construction of an infectious clone is an essential step for deciphering the virus gene functions in vivo. Using Agrobacterium based transient expression system we show that SeMV icDNA is infectious on Sesbania grandiflora and Cyamopsis tetragonoloba plants. The efficiency of icDNA infection was found to be significantly high on Cyamopsis plants when compared to that on Sesbania grandiflora. The coat protein could be detected within 6 days post infiltration in the infiltrated leaves. Different species of viral RNA (double stranded and single stranded genomic and subgenomic RNA) could be detected upon northern analysis, suggesting that complete replication had taken place. Based on the analysis of the sequences at the genomic termini of progeny RNA from SeMV icDNA infiltrated leaves and those of its 3' and 5' terminal deletion mutants, we propose a possible mechanism for 3' and 5' end repair in vivo. Mutation of the cleavage sites in the polyproteins encoded by ORF 2 resulted in complete loss of infection by the icDNA, suggesting the importance of correct polyprotein processing at all the four cleavage sites for viral replication. Complementation analysis suggested that ORF 2 gene products can act in trans. However, the trans acting ability of ORF 2 gene products was abolished upon deletion of the N-terminal hydrophobic domain of polyprotein 2a and 2ab, suggesting that these products necessarily function at the replication site, where they are anchored to membranes.