DFT and docking studies of rhodostreptomycins A and B and their interactions with solvated/nonsolvated Mg2+ and Ca2+ ions

The interactions of L-aminoglucosidic stereoisomers such as rhodostreptomycins A (Rho A) and B (Rho B) with cations (Mg²⁺, Ca²⁺, and H⁺) were studied by a quantum mechanical method that utilized DFT with B3LYP/6-311G**. Docking studies were also carried out in order to explore the surface recognition properties of L-aminoglucoside with respect to Mg²⁺ and Ca²⁺ ions under solvated and nonsolvated conditions. Although both of the stereoisomers possess similar physicochemical/antibiotic properties against Helicobacter pylori, the thermochemical values for these complexes showed that its high affinity for Mg²⁺ cations caused the hydration of Rho B. According to the results of the calculations, for Rho A–Ca²⁺(H₂O)₆, ΔH = ?72.21 kcal?mol^?1; for Rho B–Ca²⁺(H₂O)₆, ΔH = ?72.53 kcal?mol^?1; for Rho A–Mg²⁺(H₂O)₆, ΔH = ?72.99  kcal?mol^?1 and for Rho B–Mg²⁺(H₂O)₆, ΔH = ?95.00  kcal?mol^?1, confirming that Rho B binds most strongly with hydrated Mg²⁺, considering the energy associated with this binding process. This result suggests that Rho B forms a more stable complex than its isomer does with magnesium ion. Docking results show that both of these rhodostreptomycin molecules bind to solvated Ca²⁺ or Mg²⁺ through hydrogen bonding. Finally, Rho B is more stable than Rho A when protonation occurs.

Microsolvation and hydration enthalpies of CaC2O4(H2O) n (n = 0-16) and C2O4 2-(H2O) n (n = 0-14): an ab initio study

We studied hydrated calcium oxalate and its ions at the restricted Hartree–Fock RHF/6-31G* level of theory. Performing a configurational search seems to improve the fit of the HF/6-31G* level to experimental data. The first solvation shell of calcium oxalate contains 13 water molecules, while the first solvation shell of oxalate ion is formed by 14 water molecules. The first solvation shell of Ca(II) is formed by six water molecules, while the second shell contains five. At 298.15 K, we estimate the asymptotic limits (infinite dilution) of the total standard enthalpies of hydration for Ca(II), oxalate ion and calcium oxalate as ?480.78, –302.78 and –312.73 kcal mol^?1, resp. The dissociation of hydrated calcium oxalate is an endothermic process with an asymptotic limit of +470.84 kcal mol^?1.

A comparative theoretical investigation into the strength of the trigger-bond in the Na+, Mg2+ and HF complexes involving the nitro group of R–NO2 (R = –CH3, –NH2 and –OCH3) or the C = C bond of (E)-O2N–CH = CH–NO2

A comparative theoretical investigation into the change in strength of the trigger-bond upon formation of the Na⁺, Mg²⁺ and HF complexes involving the nitro group of RNO₂ (R?=? –CH₃, –NH₂, –OCH₃) or the C?=?C bond of (E)-O₂N–CH?=?CH–NO₂ was carried out using the B3LYP and MP2(full) methods with the 6-311++G**, 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. Except for the Mg²⁺?π system with (E)-O₂N–CH?=?CH–NO₂ (i.e., C₂H₂N₂O₄?Mg²⁺), the strength of the trigger-bond X–NO₂ (X?=?C, N or O) was enhanced upon complex formation. Furthermore, the increment of bond dissociation energy of the X–NO₂ bond in the Na⁺ complex was far greater than that in the corresponding HF system. Thus, the explosive sensitivity in the former might be lower than that in the latter. For C₂H₂N₂O₄?Mg²⁺, the explosive sensitivity might also be reduced. Therefore, it is possible that introducing cations into the structure of explosives might be more efficacious at reducing explosive sensitivity than the formation of an intermolecular hydrogen-bonded complex. AIM, NBO and electron density shifts analyses showed that the electron density shifted toward the X–NO₂ bond upon complex formation, leading to a strengthened X–NO₂ bond and possibly reduced explosive sensitivity.

Mineral nutrition and in vitro growth of Gerbera hybrida (Asteraceae)

The effects of mineral nutrient were examined on in vitro growth of Gerbera hybrida (G. jamesonii?×?G. viridifolia), specifically Gerbera hybrida cv. Pasadena. Four types of experiments were conducted to quantify the effects of mineral nutrients on four in vitro growth responses (quality, shoot number, leaf number, and shoot height) of gerbera and included groups of mineral nutrients (macros/mesos, micros, and Fe), individual salts (CuSO₄·5H₂O, MnSO₄·4H₂O, ZnSO₄·7H₂O, and Fe/EDTA), and the specific ions NO₃ ^?, NH₄ ⁺, and K⁺. Experiments included mixture-amount designs that are essential for separating the effects of proportion and concentration. Highly significant effects were observed in all experiments, but the mineral nutrients with the largest effects varied among the four growth responses. For example, leaf number was strongly affected by the macronutrient group in one experiment and by NH₄ ⁺ and K⁺, which were in the macronutrient group, in the NO₃ ^?/NH₄ ⁺/K⁺ ion-specific experiment, whereas quality was strongly affected by the micronutrients ZnSO₄ and Fe/EDTA. Because mineral nutrient effects varied significantly with the response measured, defining an appropriate formulation requires a clear definition of “optimal” growth.     

Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

Aims

A 3-year field experiment (October 2004–October 2007) was conducted to quantify N₂O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China.

Methods

Static chamber-GC techniques were used to measure soil N₂O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha^?1 yr^?1 or 150 kg N?ha^?1 per crop); N250 (500 kg N fertilizer ha^?1 yr^?1 kg or 250 kg N?ha^?1 per crop). Nitrate (NO ₃ ^? ) leaching losses were measured at nearby sites using free-drained lysimeters.

Results

The annual N₂O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N?ha^?1 yr^?1 corresponding to an N₂O emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil N₂O fluxes and NO ₃ ^- leaching losses can be described by a significant exponential decaying function.

Conclusions

The N₂O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO ₃ ^? , is an underrated regulating factor of soil N₂O fluxes from cropland, especially in the regions where high NO ₃ ^- leaching losses occur.     

Reductive soil disinfestation (RSD) alters gross N transformation rates and reduces NO and N2O emissions in degraded vegetable soils

Background and aims

Continuous vegetable cultivation in greenhouses can easily induce soil degradation, which considerably affects the development of sustainable vegetable production. Recently, the reductive soil disinfestation (RSD) is widely used as an alternative to chemical soil disinfestations to improve degraded greenhouse vegetable soils. Considering the importance of nitrogen (N) for plant growth and environment effect, the internal N transformation processes and rates should be well investigated in degraded vegetable soils treated by RSD, but few works have been undertaken.

Methods

Three RSD-treated and three untreated degraded vegetable soils were chosen and a ¹⁵?N tracing incubation experiment differentially labeled with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ was conducted at 25 °C under 50 % water holding capacity (WHC) for 96 h. Soil gross N transformation rates were calculated using a ¹⁵?N tracing model combined with Markov Chain Monte Carlo Metropolis algorithm (Müller et al. 2007), while the emissions of N₂O and NO were also measured.

Results

RSD could significantly enhance the soil microbial NH₄ ⁺ immobilization rate, the heterotrophic and autotrophic nitrification rates, and the NO₃ ^? turnover time. The ratio of heterotrophic nitrification to total inorganic N supply rate (mineralization + heterotrophic nitrification) increased greatly from 5.4 % in untreated vegetable soil to 56.1 % in treated vegetable soil. In addition, low release potential of NO and N₂O was observed in RSD-treated vegetable soil, due to the decrease in the NO and N₂O product ratios from heterotrophic and autotrophic nitrifications. These significant differences in gross N transformation rates, the supply processes and capacity of inorganic N, and the NO and N₂O emissions between untreated and treated vegetable soils could be explained by the elimination of accumulated NO₃ ^?, increased pH, and decreased electrical conductivity (EC) caused by RSD. Noticeably, the NO₃ ^? consumption rates were still significantly lower than the NO₃ ^? production rates in RSD-treated vegetable soil.

Conclusions

Except for improving soil chemical properties, RSD could significantly alter the supply processes of inorganic N and reduce the release potential of N₂O and NO in RSD-treated degraded vegetable soil. In order to retard the re-occurrence of NO₃ ^? accumulation, acidification and salinization and to promote the long-term productivity of greenhouse vegetable fields, the rational use of N fertilizer should be paid great attention to farmers in vegetable cultivation.     

Plasma membrane H+-ATPase in sorghum roots as affected by potassium deficiency and nitrogen sources

We studied the influence of inorganic nitrogen sources (NO₃ ^? or NH₄ ⁺) and potassium deficiency on expression and activity of plasma membrane (PM) H⁺-ATPase in sorghum roots. After 15 d of cultivation at 0.2 mM K⁺, the plants were transferred to solutions lacking K⁺ for 2 d. Then, K⁺ depletion assays were performed in the presence or absence of vanadate. Further, PMs from K⁺-starved roots were extracted and used for the kinetic characterization of ATP hydrolytic activity and the immunodetection of PM H⁺-ATPase. Two major genes coding PM H⁺-ATPase (SBA1 and SBA2) were analyzed by real-time PCR. PM H⁺-ATPase exhibited a higher V_max and K_m in NH₄ ⁺-fed roots compared with NO₃ ^? -fed roots. The optimum pH of the enzyme was slightly lower in NO₃ ^? -fed roots than in NH₄ ⁺-fed roots. The vanadate sensitivity was similar. The expressions of SBA1 and SBA2 increased in roots grown under NH₄ ⁺. Concomitantly, an increased content of the enzyme in PM was observed. The initial rate of K⁺ uptake did not differ between plants grown with NO₃ ^? or NH₄ ⁺, but it was significantly reduced by vanadate in NH₄ ⁺-grown plants.     

On the properties of Se ⋯N interaction: the analysis of substituent effects by energy decomposition and orbital interaction

The nature and strength of intermolecular Se ?N interaction between selenium-containing compounds HSeX (X = CH₃, NH₂, CF₃, OCH₃, CN, OH, NO₂, Cl, F), and NH₃ have been investigated at the MP2/aug-cc-pVDZ level. The Se ?N interaction is found to be dependent on the substituent groups, which greatly affect the positive electrostatic potential of Se atoms and the accepting electron ability of X-Se σ ^? antibonding orbital. Energy decomposition of the Se ?N interaction reveals that electrostatic and induction forces are comparable in the weak-bonded complexes and induction becomes more significant in the complexes with strong electron-withdrawing substituents. Natural bond orbital (NBO) analysis indicates that the primary source of the induction is the electron transfer from the N lone pair to the X-Se σ ^? antibonding orbital. The geometry of the complex and the interaction directionality of NH₃ to X-Se bond can be regarded as a consequence of the exchange-repulsion. The topological analysis on the electron density reveals the nature of closed-shell interaction in these X-Se ?N contacts. The Se ?N interaction in the complexes with the strong electron-withdrawing substituent has a partly covalent character.     

Habitability of the early earth: Clues from the physiology of nitrogen fixation and photosynthesis

In the absence of direct evidence concerning the nature of the early Earth environments, it is acceptable under the uniformitarian principle to attempt to define primitive habitats from modern procaryotic physiology. Combining the rock and fossil record with present phylogenetic reconstuctions, application of this paleoecological approach to the evolutionary biochemistry and physiology of nitrogen fixation and photosynthesis leads to several inferences about the nature of Archean environments:

1. To stimulate nitrogenase evolution and avoid its repression, the activity of the NH ₄ ⁺ ion was less than 10^?3, and probably lower.
2. To be consistent with a moderately protective ozone screen, while not also repressing nitrogenase activity, incursions of abiotic dissolved oxygen at levels in the range 10^?1.2?10^?3.5 PAL would have been acceptable.
3. To induce the formation and activity of RuBP carboxylase, the pCO₂ was less than 100 PAL.
4. To support Photosystem I activity, sulfide concentrations of at least 10^?4 M were present in the photic zone.
5. To avoid a too-rapid oxidation of sulfide, the pH was probably between 6–7, where H₂S exceeds HS^?.

Evolutionary ‘pressure’ to stimulate the later development of oxygenic photosynthesis (Photosystem II), would require several subsequent habitat modifications:

1. Lowering the sulfide to < 10^?4 M to inhibit Photosystem I.
2. Raising the pH above neutral (HS^? > H₂S), to mediate more rapid oxidation of HS^?.
3. Maintaining either an illumination below 300–400 lux (to avoid photosynthetic O₂ self-repression of nitrogen fixation), or an adequate local source of combined nitrogen (aNH ₄ ⁺ > 10^?4) to repress nitrogen fixation entirely.

     

Fourier-transform infrared spectroscopy of Pediastrum duplex: characterization of a micro-population isolated from a eutrophic lake

Fourier-transform infrared (FTIR) spectroscopy was carried out on single colonies of Pediastrum duplex present in air-dried preparations of mixed phytoplankton samples isolated from a eutrophic freshwater lake. FTIR absorption spectra had 12 distinct bands over the wavenumber range 3300–900?cm^?1 which were tentatively assigned to a range of chemical groups, including –OH (residual water, wavenumber 3299?cm^?1), –CH2 (lipid, 2924), –C=O (cellulose, 1739), amide (protein, 1650 and 1542), >P=O (nucleic acid, 1077) and –C–O (starch, 1151 and 1077). Measurement of band areas identified residual water, protein and starch as the major detectable constituents. Areas of single bands and combined bands of –CH₂, –C–O and >P=O species normalized to protein (to correct for differences in specimen hydration and thickness) showed wide variation between colonies, indicating environmental heterogeneity. Correlation analysis demonstrated close statistical associations between different molecular species. Particularly high levels of correlation between bands 3/4 (CH₂), 6/7 (amide) and 8/9 (–CH₃) was consistent with their joint origin from the same molecular species. The isolation of bands 11 and 12 in the correlation pattern was confirmed by factor analysis, suggesting that variation in the level of starch is statistically unrelated to other macromolecules being monitored. The use of FTIR spectroscopy to characterize an algal micro-population within mixed phytoplankton has potential for future studies on biodiversity and environmental interactions at the species level.     

The concentration controlled 1D and 2D supramolecular isomers of lanthanide with 2,2’-bipyridyl-3,3’-dicarboxylate and phenanthroline

The reactions of 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂bpdc) and 1,10-phenanthroline (phen) with lanthanide (III) salts in different concentrations under hydrothermal conditions formed two series of supramolecular isomers of 1D zigzag chains of [Ln(bpdc)_1.5(phen)(H₂O)]_n·3nH₂O (1Ln·3H₂O), and 2D frameworks of [Ln(bpdc)_1.5(phen)(H₂O)]_n (2Ln), (Ln = Ho, Er, Tm, and Yb). At lower concentrations, the supramolecular isomers of 1Ln were formed, in which each isomer has a dinuclear centrosymmetric dimeric unit of [Ln₂(phen)₂(H₂O)₂(μ₂-bpdc)₂]²⁺, and the dimeric units are alternately connected by μ₂-bpdc²⁻ to form a 1D zigzag chain of 1Ln. At higher concentrations, the supramolecular isomers of 2Ln were formed. All the compounds of 2Ln are isomorphous, in which two μ₃-bpdc²⁻ bridge two [Ln(phen)(H₂O)]³⁺ units to yield a 1D double-chains of [Ln₂(phen)₂(H₂O)₂(bpdc)₂]_n²ⁿ⁺, and [Ln₂(phen)₂(H₂O)₂(bpdc)₂]_n²ⁿ⁺ chains are further connected by μ₄-bpdc²⁻ to form a 2D network of [Ln(bpdc)_1.5(phen)(H₂O)]_n. The 2D sheets are combined through the intersheet π-π interactions between the adjacent phen molecules to form a 3D structure of 2Ln. The compounds of Er(III), and Yb(III) exhibit corresponding characteristic photoluminescence in the near-infrared (NIR) region, in which 1Ln and 2Ln show obviously different emission intensity due to their different structures.     

Annual nitrous oxide emissions from open-air and greenhouse vegetable cropping systems in China

Aims

A field experiment was conducted to quantify annual nitrous oxide (N₂O) fluxes from control and fertilized plots under open-air and greenhouse vegetable cropping systems in southeast China. We compiled the reported global field annual N₂O flux measurements to estimate the emission factor of N fertilizer for N₂O and its background emissions from vegetable fields.

Methods

Fluxes of N₂O were measured using static chamber-GC techniques over the 2010–2011 annual cycle with multiple cropping seasons.

Results

The mean annual N₂O fluxes from the controls were 46.1?±?2.3 μg N₂O-N m^?2 hr^?1 and 68.3?±?4.1 μg N₂O-N m^?2 hr^?1 in the open-air and greenhouse vegetable systems, respectively. For the plots receiving 900 kg?N?ha^?1, annual N₂O emissions averaged 90.6?±?8.9 μg N₂O-N m^?2 hr^?1 and 106.4?±?6.6 μg N₂O-N?m^?2 hr^?1 in the open-air and greenhouse vegetable systems, respectively. By pooling published field N₂O flux measurements taken over or close to a full year, the N₂O emission factor for N fertilizer averaged 0.63?±?0.09 %, with a background emission of 2.67?±?0.80 kg N₂O-N ha^?1 in Chinese vegetable fields. Annual N₂O emissions from Chinese vegetable systems were estimated to be 84.7 Gg N₂O-N yr^?1, consisting of 72.5 Gg N₂O-N yr^?1 and 12.2 Gg N₂O-N yr^?1 in the open-air and greenhouse vegetable systems, respectively.

Conclusions

While N₂O emissions from the greenhouse vegetable cropping system tended to be slightly higher compared to the open-air system in our experiment, the synthesis of literature data suggests that N₂O emissions would be greater at low N-rates but smaller at high N-rates in greenhouse systems than in open-air vegetable cropping systems. The estimates of this study suggest that vegetable cropping systems covering 11.4 % in national total cropping area, contributed 21–25 % to the total N₂O emission from Chinese croplands.     

Ionic balance,proton efflux,nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N₂ fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH ₄ ⁺ , a mixture of NH ₄ ⁺ and NO ₃ ^? producing the highest yields. Growth was severely reduced when solely dependent on N₂ fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N₂-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO ₃ ^? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO ₃ ^? and NH ₄ ⁺ , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH ₄ ⁺ , NO ₃ ^? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO ₃ ^? +NH ₄ ⁺ plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH ₄ ⁺ plants than in the NO ₃ ^? plants. Measured extrusions of H⁺ or OH^? (HCO ₃ ^? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N₂ fixation amounted to 0.45–0.55 meq H⁺. (mmol N_org)^?1. Without acidity control and in the presence of NH ₄ ⁺ , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N₂-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.     

Which root traits determine nitrogen uptake by alpine plant species on the Tibetan Plateau?

Background and aims

Nitrogen (N) is one of the most important limiting factors influencing plant growth and reproduction in alpine and tundra ecosystems. However, in situ observations of the effects of root traits on N absorption by alpine plant species are still lacking.

Methods

We investigated the rates of N uptake and the effect of root characteristics in ten common herbaceous alpine plant species using a ¹⁵N isotope tracer technique and the root systems of plants growing in a semi-arid steppe environment on the Tibetan Plateau. Our objective was to determine the root traits (root biomass, volume, surface area, average diameter, length, specific root length and specific root area) that make the largest contribution to the total uptake of N (¹⁵N–NO₃ ^?, ¹⁵N–NH₄ ⁺ or ¹⁵N–glycine) by alpine plant species.

Results

Monocotyledonous species had higher absorption rates for ¹⁵N–NH₄ ⁺, ¹⁵N–NO₃ ^?, ¹⁵N–glycine and total ¹⁵N than dicotyledonous species (P < 0.05). The root biomass, volume, surface area and average diameter were negatively correlated with the absorption capacity for ¹⁵N–NH₄ ⁺, ¹⁵N–NO₃ ^? and total ¹⁵N across the ten alpine plant species. However, the specific root length and the specific root area had significantly positive effects on the uptake of N.

Conclusions

In contrast with traditional views on the uptake of N, the N uptake rate was not improved by a larger root volume or root surface area for these alpine plant species in a high-altitude ecosystem. Root morphological traits had greater impacts on N absorption than traits related to the root system size in alpine herbaceous plants.

     

Nitrogen Metabolism Genes from Temperate Marine Sediments

In this study, we analysed metagenomes along with biogeochemical profiles from Skagerrak (SK) and Bothnian Bay (BB) sediments, to trace the prevailing nitrogen pathways. NO₃ ^? was present in the top 5 cm below the sediment-water interface at both sites. NH₄ ⁺ increased with depth below 5 cm where it overlapped with the NO₃ ^? zone. Steady-state modelling of NO₃ ^? and NH₄ ⁺ porewater profiles indicates zones of net nitrogen species transformations. Bacterial protease and hydratase genes appeared to make up the bulk of total ammonification genes. Genes involved in ammonia oxidation (amo, hao), denitrification (nir, nor), dissimilatory NO₃ ^? reduction to NH₄ ⁺ (nfr and otr) and in both of the latter two pathways (nar, nap) were also present. Results show ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are similarly abundant in both sediments. Also, denitrification genes appeared more abundant than DNRA genes. 16S rRNA gene analysis showed that the relative abundance of the nitrifying group Nitrosopumilales and other groups involved in nitrification and denitrification (Nitrobacter, Nitrosomonas, Nitrospira, Nitrosococcus and Nitrosomonas) appeared less abundant in SK sediments compared to BB sediments. Beggiatoa and Thiothrix 16S rRNA genes were also present, suggesting chemolithoautotrophic NO₃ ^? reduction to NO₂ ^? or NH₄ ⁺ as a possible pathway. Our results show the metabolic potential for ammonification, nitrification, DNRA and denitrification activities in North Sea and Baltic Sea sediments.     

Culture medium optimization for improved puerarin production by cell suspension cultures of Pueraria tuberosa (Roxb. ex Willd.) DC.

The effects of carbon, nitrogen, phosphate, and copper on cell growth and production of the isoflavone puerarin by suspension cultures of Pueraria tuberosa (Roxb. ex. Willd.) DC were investigated. Among the various sugars evaluated (glucose, galactose, fructose, maltose, and sucrose), use of sucrose in the medium led to the maximum accumulation of puerarin. A sucrose-feeding strategy in which additional sucrose was added to the flasks 15?d into the culture cycle stimulated both cell biomass and puerarin production. The maximum production of puerarin was obtained when a concentration balance of 20:60?mM NH ₄ ⁺ /NO ₃ ^? was used as the nitrogen source. Alteration in the concentration balance of nitrogen components (NH ₄ ⁺ /NO ₃ ^? 60:20?mM) or the use of either NH ₄ ⁺ or NO ₃ ^? alone decreased biomass production and puerarin accumulation compared with the control culture (NH ₄ ⁺ /NO ₃ ^? 20:20?mM). High amounts of phosphate (2.5 and 5?mM) in the medium inhibited puerarin production whereas 0.625?mM phosphate promoted puerarin production (68.3???g/g DW on day?25). An increase in Cu²⁺ concentration from 0.025 to 0.05?mg/l in the P. tuberosa cell culture medium resulted in a 2.2-fold increase in puerarin production (up to 141???g/g DW on day?25) but reduced cell culture biomass.     

Acid-base and gas-transfer properties of the blood of newborn infants

The concentration of HCO ₃ ^? , pH, pO₂, sO₂, and pCO₂ were measured in the total umbilical blood of neonates born in January–February (n = 169) and June–July (n = 172). The former group displayed higher values of pH, pO₂, and sO₂, whereas pCO₂ and the concentration of HCO ₃ ^? were higher in the latter group. There was a 70–80% coincidence of the variants in both groups (the regions of statistical transgressions); seasonal factors were responsible for 20–30% of the differences.     

Changes in the Functional Activity of Phi11 Cro Protein is Mediated by Various Ions

Phi11, a temperate bacteriophage of Staphylococcus aureus, has been found to harbor a cro repressor gene which facilitates Phi11 to adopt the lytic mode of development. The Cro protein has been found to bind very specifically to a 15-bp operator DNA, located in the Phi11 cI–cro intergenic region [1]. To investigate the effects exerted by different ions upon the interaction between Cro and its cognate operator DNA, we have employed gel shift assays as well as circular dichroism spectral analysis. In this communication, we have shown that NH₄ ⁺ and acetate^? ions better facilitated the binding of Cro with its cognate operator as compared to Na⁺, K⁺ and Li⁺. Interestingly, Mg²⁺, carbonate^2? and Citrate^3? have an inhibitory effect upon the binding. The effect of the said ions upon the structure of Cro was also investigated by circular dichroism and it was found that other than Citrate^3? ions, none of the other ions destabilised the protein. On the other hand, Mg²⁺ and carbonate^2? ions maintained the structure of the protein but severely hampered its functional activity. Citrate^3? ions severely unfolded Cro and also inhibited its function. Considering all the data, NH₄ ⁺ and acetate^? ions appeared to be more suitable in maintaining the biological activity of Cro.