Quantifying Lipari–Szabo modelfree parameters from 13CO NMR relaxation experiments

It is proposed to obtain effective Lipari–Szabo order parameters and local correlation times for relaxation vectors of protein ¹³CO nuclei by carrying out a ¹³CO-R₁ auto relaxation experiment, a transverse CSA/dipolar cross correlation and a transverse ¹³CO CSA/¹³CO–¹⁵N CSA/dipolar cross correlation experiment. Given the global rotational correlation time from ¹⁵N relaxation experiments, a new program COMFORD (CO-Modelfree Fitting Of Relaxation Data) is presented to fit the ¹³CO data to an effective order parameter , an effective local correlation time and the orientation of the CSA tensor with respect to the molecular frame. It is shown that the effective is least sensitive to rotational fluctuations about an imaginary axis and most sensitive to rotational fluctuations about an imaginary axis parallel to the NH bond direction. As such, the information is fully complementary to the ¹⁵N relaxation order parameter, which is least sensitive to fluctuations about the NH axis and most sensitive to fluctuations about the axis. The new paradigm is applied on data of Ca²⁺ saturated Calmodulin, and on available literature data for Ubiquitin. Our data indicate that the order parameters rapport on slower, and sometimes different, motions than the ¹⁵N relaxation order parameters. The CO local correlation times correlate well with the calmodulin’s secondary structure. Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at .     

Alternate-site isotopic labeling of ribonucleotides for NMR studies of ribose conformational dynamics in RNA

Heteronuclear NMR spin relaxation studies of conformational dynamics are coming into increasing use to help understand the functions of ribozymes and other RNAs. Due to strong magnetic interactions within the ribose ring, however, these studies have thus far largely been limited to ¹³C and ¹⁵N resonances on the nucleotide base side chains. We report here the application of the alternate-site ¹³C isotopic labeling scheme, pioneered by LeMaster for relaxation studies of amino acid side chains, to nucleic acid systems. We have used different strains of E. coli to prepare mononucleotides containing ¹³C label in one of two patterns: Either C1′ or C2′ in addition to C4′, termed (1′/2′,4′) labeling, or nearly complete labeling at the C2′ and C4′ sites only, termed (2′,4′) labeling. These patterns provide isolated H spin systems on the labeled carbon atoms and thus allow spin relaxation studies without interference from scalar or dipolar coupling. Using relaxation studies of AMP dissolved in glycerol at varying temperature to produce systems with correlation times characteristic of different size RNAs, we demonstrate the removal of errors due to interaction in T ₁ measurements of larger nucleic acids and in T _1ρ measurements in RNA molecules. By extending the applicability of spin relaxation measurements to backbone ribose groups, this technology should greatly improve the flexibility and completeness of NMR analyses of conformational dynamics in RNA.     

Effects of common soil anions and pH on the uptake and accumulation of perchlorate in lettuce

A mechanistic understanding of perchlorate () entry into plants is important for establishing the human health risk associated with consumption of contaminated produce and for assessing the effectiveness of phytoremediation. To determine whether common soil anions affect uptake and accumulation in higher plants, a series of competition experiments using lettuce (Lactuca sativa L.) were conducted between (50 nM) and (4–12 mM), (1–10 mM), or Cl⁻ (5–15 mM) in hydroponic solution. The effects of (0–5 mM) and pH (5.5–7.5) on uptake were also examined. Increasing in solution significantly reduced the amount of taken up by green leaf, butter head, and crisphead lettuces. Sulfate and Cl⁻ had no significant effects on uptake in lettuce over the concentrations tested. Increasing pH significantly reduced the amount of taken up by crisphead and green leaf lettuces, whereas increasing significantly reduced uptake in butter head lettuce. The inhibition by across all lettuce genotypes suggests that may share an ion carrier with , and the decrease in uptake with increasing pH or provides macroscopic evidence for cotransport across the plasma membrane.     

Quantitative Γ-HCNCH: determination of the glycosidic torsion angle χ in RNA oligonucleotides from the analysis of CH dipolar cross-correlated relaxation by solution NMR spectroscopy

A novel NMR pulse sequence is introduced to determine the glycosidic torsion angle χ in ¹³C,¹⁵N-labeled oligonucleotides. The quantitative Γ-HCNCH measures the dipolar cross-correlated relaxation rates (pyrimidines) and (purines). Cross-correlated relaxation rates of a ¹³C,¹⁵N-labeled RNA 14mer containing a cUUCGg tetraloop were determined and yielded χ-angles that agreed remarkably well with data derived from the X-ray structure of the tetraloop. In addition, the method was applied to the larger stemloop D (SLD) subdomain of the Coxsackievirus B3 cloverleaf 30mer RNA and the effect of anisotropic rotational motion was examined for this molecule. It could be shown that the χ-angle determination especially for nucleotides in the anti conformation was very accurate and the method was ideally suited to distinguish between the syn and the anti-conformation of all four types of nucleotides. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Can biological nitrification inhibition (BNI) genes from perennial Leymus racemosus (Triticeae) combat nitrification in wheat farming?

Using a recombinant luminescent Nitrosomonas europaea assay to quantify biological nitrification inhibition (BNI), we found that a wild relative of wheat (Leymus racemosus (Lam.) Tzvelev) had a high BNI capacity and releases about 20 times more BNI compounds (about 30 ATU g⁻¹ root dry weight 24 h⁻¹) than Triticum aestivum L. (cultivated wheat). The root exudate from cultivated wheat has no inhibitory effect on nitrification when applied to soil; however, the root exudate from L. racemous suppressed formation and kept more than 90% of the soil’s inorganic-N in the -form for 60 days. The high-BNI capacity of L. racemosus is mostly associated with chromosome Lr#n. Two other chromosomes Lr#J, and Lr#I also have an influence on BNI production. Tolerance of L. racemosus to is controlled by chromosome 7Lr#1-1. Sustained release of BNI compounds occurred only in the presence of in the root environment. Given the level of BNI production expressed in DALr#n and assuming normal plant growth, we estimated that nearly 87,500,000 ATU of BNI activity ha⁻¹ day⁻¹ could be released in a field of vigorously growing wheat; this amounts to the equivalent of the inhibitory effect from the application of 52.5 g of the synthetic nitrification inhibitor nitrapyrin (one AT unit of BNI activity is equivalent to 0.6 μg of nitrapyrin). At this rate of BNI production it would take only 19 days for a BNI-enabled wheat crop to produce the inhibitory power of a standard commercial application of nitrapyrin, 1 kg ha⁻¹. The synthetic nitrification inhibitor, dicyandiamide, blocked specifically the AMO (ammonia monooxygenase) pathway, while the BNI from L. racemosus blocked the HAO (hydroxylamine oxidoreductase) pathway in Nitrosomonas. Here we report the first finding of high production of BNI in a wild relative of any cereal and its successful introduction and expression in cultivated wheat. These results demonstrate the potential for empowering the new generation of wheat cultivars with high-BNI capacity to control nitrification in wheat-production systems. Responsible Editor: Hans Lambers.     

(H)NCAHA and (H)CANNH experiments for the determination of vicinal coupling constants related to the ϕ-torsion angle

Summary A set of three-dimensional triple-resonance experiments is described which provide , , and coupling constants. The pulse sequences generate E.COSY-like multiplet patterns and comprise a magnetization transfer from the amide proton to the α-proton or vice versa via the directly bound heteronuclei. For residues with the ¹H^α spin resonating close to the H₂O signal, a modified HNCA experiment can be employed to measure the vicinal ¹H^N,¹H^α couplings. Ambiguities associated with the conversion of values into ϕ-angle constraints for protein structure determination can be resolved with the knowledge of the heteronuclear ³J-couplings. In favourable cases, stereospecific assignments of glycine α-protons can be obtained by employing the experiments described here in combination with NOE data. The methods are applied to flavodoxin from Desulfovibrio vulgaris.     

The effect of temperature on post-feeding ammonia excretion and oxygen consumption in the southern catfish

The post-prandial rates of ammonia excretion (TAN) and oxygen consumption in the southern catfish (Silurus meridionalis) were assessed at 2 h intervals post-feeding until the rates returned to those of the fasting rates, at 17.5, 22.5, 27.5, and 32.5°C, respectively. Both fasting TAN and increased with temperature, and were lower than those previously reported for many fish species. The relationship between fasting TAN (mmol NH₃–N kg⁻¹ h⁻¹) and temperature (T, °C) was described as: fasting TAN = 0.144e ^0.0266T (r = 0.526, n = 27, P < 0.05). The magnitude of ammonia excretion and its ratio to total N intake during the specific dynamic action (SDA) tended to increase initially, and then decrease with increasing temperature. The ammonia quotient (AQ), calculated as mol NH₃–N/mol O₂, following feeding decreased as temperature increased. The relationship between AQ during SDA and temperature was described as: AQ_{during SDA} = 0.303e ^−0.0143T (r = 0.739, n = 21, P < 0.05). Our results suggest that ammonia excretion and oxygen consumption post-feeding are operating independently of each other. Furthermore, it appears that the importance of protein as a metabolic substrate in postprandial fish decreases with temperature.     

Bifurcation Analysis of Genetically Engineered Pacemaking in Mammalian Heart

Genetically engineered pacemaking in ventricular cells has been achieved by down-regulation of the time independent inward rectifying current (I _K1), or insertion of the hyperpolarisation-activated funny current (I _f). We analyse the membrane system (i.e. ionic concentrations clamped) of an epicardial Luo-Rudy dynamic cell model using continuation algorithms with the maximum conductance () of I _K1 and I _f as bifurcation parameters. Pacemaker activity can be induced either via Hopf or homoclinic bifurcations. As _K1 is decreased by ≈74%, autorhythmicity emerged via a homoclinic bifurcation, i.e., the periodicity first appear with infinitely large periods. In contrast, the insertion of _f induced periodicity via a subcritical Hopf bifurcation at _f≈ 0.25 mSμF⁻¹. Stable autorhythmic action potentials occurred at _f > 0.329 mSμF⁻¹.     

Pairwise NMR experiments for the determination of protein backbone dihedral angle Φ based on cross-correlated spin relaxation

Novel cross-correlated spin relaxation (CCR) experiments are described, which measure pairwise CCR rates for obtaining peptide dihedral angles Φ. The experiments utilize intra-HNCA type coherence transfer to refocus 2-bond coupling evolution and generate the or multiple quantum coherences which are required for measuring the desired CCR rates. The contribution from other coherences is also discussed and an appropriate setting of the evolution delays is presented. These CCR experiments were applied to ¹⁵N- and ¹³C-labeled human ubiquitin. The relevant CCR rates showed a high degree of correlation with the Φ angles observed in the X-ray structure. By utilizing these CCR experiments in combination with those previously established for obtaining dihedral angle Ψ, we can determine high resolution structures of peptides that bind weakly to large target molecules.     

Inheritance of foliar stable carbon isotope discrimination and third-year height in Pinus taeda clones on contrasting sites in Florida and Georgia

Quantifying foliar stable carbon isotope discrimination (Δ) is a powerful approach for understanding genetic variation in gas exchange traits in large populations. The genetic architecture of Δ and third-year height is described for more than 1,000 clones of Pinus taeda tested on two contrasting sites. for Δ was 0.14 (±0.03), 0.20 (±0.07), and 0.09 (±0.04) at Florida, Georgia, and across sites, respectively. for stable carbon isotope discrimination ranged from 0.25 (±0.03) at the Florida site to 0.33 (±0.03) at the Georgia site, while the across-site estimate of was 0.19 (±0.02). For third-year height, ranged from 0.13 (±0.05) at the Georgia site to 0.20 (±0.06) at the Florida site with an across-site estimate of 0.09 (±0.05). Broad-sense heritability estimates for third-year height were 0.23 (±0.03), 0.28 (±0.03), and 0.13 (±0.02) at the Florida site, Georgia site, and across sites, respectively. Type B total genetic correlation for Δ was 0.70 ± 0.06, indicating that clonal rankings were relatively stable across sites, while for third-year height, rankings of clones were more unstable across the two trials . Third-year height and Δ were negatively correlated at the parental , full-sib family , and clonal levels, suggesting that genetic variation for Δ in P. taeda may be a result of differences in photosynthetic capacity. We conclude that Δ may be a useful selection trait to improve water-use efficiency and for guiding deployment decisions in P. taeda.     

Concentration-Dependent Effects on Intracellular and Surface pH of Exposing <Emphasis Type="Italic">Xenopus</Emphasis> oocytes to Solutions Containing NH<Subscript>3</Subscript>/NH<Subscript>4</Subscript><Superscript>+</Superscript>

Others have shown that exposing oocytes to high levels of (10–20 mM) causes a paradoxical fall in intracellular pH (pH_i), whereas low levels (e.g., 0.5 mM) cause little pH_i change. Here we monitored pH_i and extracellular surface pH (pH_S) while exposing oocytes to 5 or 0.5 mM NH₃/NH₄ ⁺. We confirm that 5 mM causes a paradoxical pH_i fall (−ΔpH_i ≅ 0.2), but also observe an abrupt pH_S fall (−ΔpH_S ≅ 0.2)—indicative of NH₃ influx—followed by a slow decay. Reducing [NH₃/NH₄ ⁺] to 0.5 mM minimizes pH_i changes but maintains pH_S changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates −ΔpH_S at both levels. During removal of 0.5 or 5 mM NH₃/NH₄ ⁺, failure of pH_S to markedly overshoot bulk extracellular pH implies little NH₃ efflux and, thus, little free cytosolic NH₃/NH₄ ⁺. A new analysis of the effects of NH₃ vs. NH₄ ⁺ fluxes on pH_S and pH_i indicates that (a) NH₃ rather than NH₄ ⁺ fluxes dominate pH_i and pH_S changes and (b) oocytes dispose of most incoming NH₃. NMR studies of oocytes exposed to ¹⁵N-labeled show no significant formation of glutamine but substantial accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pH_i and pH_S demonstrate that NH₃ flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane.

Factors affecting denitrification in agricultural headwater streams in Northeast Ohio,USA

As a result of increased anthropogenic nitrogen (N) loading in surface waters of agricultural watersheds, there is enhanced interest to understand and quantify N removal mechanisms. Denitrification, an important N removal mechanism in aquatic systems, may contribute to reducing N pollution in agricultural headwater streams. However, the key factors controlling this process in lotic systems remain unclear. The objective of our study was to examine the factors regulating rates of denitrification in the sediments of agricultural headwater streams in the mid-western USA. Denitrification rates were variable among streams and treatments (<0.1–28.0 μg N g AFDM⁻¹ h⁻¹) and on average, were higher than those reported for similar headwater streams. Carbon quantity and quality, and pH had no effect on denitrification, while temperature and nitrate ( ) concentrations had a positive effect on rates of denitrification. Specifically, controlled denitrification following Michaelis-Menten kinetics. We calculated a value of k_m (1.0 mg -N L^-1) that was comparable to other studies in aquatic sediments but was well below the median in-stream concentrations (5.2–17.4 mg -N L⁻¹) observed at the study sites. Despite high rates of denitrification, this removal mechanism is most likely saturated in the agricultural headwater streams we examined, suggesting that these systems are not effective at removing in-stream N. Handling editor: D. Ryder     

Report on non-temperature related variations in CO<Subscript>2</Subscript> efflux rates from young tree stems in the dormant season

Respiration rates are reported to increase exponentially with temperature. Respiration rates of woody tissues are commonly measured as CO₂ efflux rates () from that tissue. However, this paper describes clear variations in stem that were not related to temperature for the case of a young beech (Fagus sylvatica L.) and oak (Quercus robur L.) tree during the dormant season. The CO₂ concentration ([CO₂]) in the xylem of the beech tree showed similar temperature-independent variations. The trees were grown in a growth chamber in which radiation patterns and temperature were kept constant. was measured with an IRGA connected to cuvettes surrounding a stem segment. Xylem [CO₂] was measured in situ using a CO₂ microelectrode. Depressions in and [CO₂] occurred during the light period, despite equal temperatures in the light and dark period. Explanations found in literature for discrepancies in the exponential relationship between temperature and are the influence of (1) sap flow or (2) decreased cell water content. However, (1) the variations were observed in the dormant season, when no sap flow was observed yet, and (2) reduced cell water content was not likely to be apparent as differences in stem transpiration rates between the dark and light period were not significant. Hence, previously formulated theories failed to explain our results. This work therefore provides a new ground for discussion on other possible causes of daytime depressions in . One might be the refixation of respired CO₂ by corticular photosynthesis in the stem parts adjacent to the stem segment enclosed by the cuvette.     

Determination of heteronuclear three-bond J-coupling constants in peptides by a simple heteronuclear relayed E.COSY experiment

Summary A simple heteronuclear relayed E.COSY pulse sequence with a minimum number of pulses is proposed for the quantitative determination of heteronuclear three-bond J-coupling constants in uniformly ¹³C-enriched polypeptide samples. Numerous heteronuclear three-bond coupling constants, including , , , and , can be determined for each residue from a single heteronuclear relayed E.COSY spectrum. Couplings relevant for stereospecific assignments as well as for the determination of dihedral angles in the amino acid backbone and in side chains are obtained. The method is demonstrated on the uniformly ¹³C-enriched decapeptide antamanide (-Val¹-Pro²-Pro³-Ala⁴-Phe⁵-Phe⁶-Pro⁷-Pro⁸-Phe⁹-Phe¹⁰-).     

Measurement of eight scalar and dipolar couplings for methine–methylene pairs in proteins and nucleic acids

A new 3D, spin-state-selective coherence transfer NMR experiment is described that yields accurate measurements for eight scalar or dipolar couplings within a spin system composed of a methylene adjacent to a methine group. Implementations of the experiment have been optimized for proteins and for nucleic acids. The experiments are demonstrated for C–C moieties of the third IgG-binding domain from Streptococcal Protein G (GB3) and for C –C groups in a 24-nt RNA oligomer. Chemical shifts of C, C and H (respectively C , C and H ) are dispersed in the three orthogonal dimensions, and the absence of heteronuclear decoupling leads to distinct and well-resolved E.COSY multiplet patterns. In an isotropic sample, the E.COSY displacements correspond to ¹J_CH, ²J_CH2+²J_CH3, ²J_CH, ¹J_CH2+¹J_CH3, ¹J_CH2–²J_H2H3, ¹J_CH3–²J_H2H3, ³J_HH2 and ³J_HH3 for proteins, and ¹J , ²J J , ²J , ¹J +¹J , ¹J J , ¹J J , ³J and ³J in nucleic acids. The experiment, based on relaxation-optimized spectroscopy, yields best results when applied to residues where the methine–methylene group corresponds to a reasonably isolated spin system, as applies for C, F, Y, W, D, N and H residues in proteins, or the C –C groups in nucleic acids. Splittings can be measured under either isotropic or weakly aligned conditions, yielding valuable structural information both through the ³J couplings and the one-, two- and three-bond dipolar interactions. Dipolar couplings for 10 out of 13 sidechains in GB3 are found to be in excellent agreement with its X-ray structure, whereas one residue adopts a different backbone geometry, and two residues are subject to extensive ₁ rotamer averaging. The abundance of dipolar couplings can also yield stereospecific assignments of the non-equivalent methylene protons. For the RNA oligomer, dipolar data yielded stereospecific assignments for six out of the eight C H₂ groups in the loop region of the oligomer, in all cases confirmed by ¹J ^{1} $$" align="middle" border="0"> J , and H resonating downfield of H .Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s10858-005-0175-z.     

Theoretical study of AlH(2+)n (n=1-7) dications

The structures and stability of 1–7 dications were calculated at the ab initio MP2/aug-cc-pVTZ level of theory. The dications AlH²⁺ 1 and 2 were characterized to be unstable thermodynamically. However, these and the stable dications, 3–7 have considerable kinetic barriers for deprotonation. Each of the structures 3–7 contains one or more two-electron three-center (2e–3c) bonds. Aluminum atoms of these dications carry most of the positive charges, as indicated by NBO charge calculations.Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday     

Genetic transformation of <Emphasis Type="Italic">Gentiana macrophylla</Emphasis> with <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>: growth and production of secoiridoid glucoside gentiopicroside in transformed hairy root cultures

Hairy root cultures of Gentiana macrophylla were established by infecting the different explants four Agrobacterium rhizogenes strains namely A₄GUS, R1000, LBA 9402 and ATCC11325, and hairy root lines were established with A. rhizogenes strain R1000 in 1/2 MS + B₅ medium. Initially, 42 independent hairy root clones were maintained and seven clones belongs to different category were evaluated for growth, morphology, integration and expression of Ri T-DNA genes, and alkaloid contents in dry root samples. On the basis of total root elongation, lateral root density and biomass accumulation on solid media, hairy root clones were separated into three categories. PCR and Southern hybridization analysis revealed both left and right T-DNA integration in the root clones and RT-PCR analysis confirmed the expression of hairy root inducible gene. GUS assay was also performed to confirm the integration of left T-DNA. The accumulation of considerable amounts of the root-specific secoiridoid glucosides gentiopicroside was observed in GM1 ( and ) and the GM2 ( and DNA) type clones in considerably higher amount whether as two but callus-type clones (GM3) accumulated much less or only very negligible amounts of gentiopicroside. Out of four media composition the 1/2 MS + B₅ vitamin media was found most suitable. We found that initial establishment of root cultures largely depends on root:media ratio. Maximum growth rate was recorded in 1:50 root:media ratio. The maximum biomass in terms of fresh weight (33-fold) was achieved in 1/2 MS + B₅ media composition after 35 days in comparison to sixfold increase in control. The biomass increase was most abundant maximum from 15 to 30 days. Influence of A. rhizogenes strains and Ri plasmid of hairy root induction, the possible role of the T_L-DNA and T_R-DNA genes on growth pattern of hairy root, initial root inoculum:media ratio and effect of media composition is discussed.     

A set of HA-detected experiments for measuring scalar and residual dipolar couplings

A new set of HCACO based three-dimensional NMR experiments for measuring residual dipolar couplings in proteins is presented. Using spin-state selection and editing in three dimensions, the experiments allow accurate measurement of intraresidual , and scalar and residual dipolar couplings of ¹⁵N/¹³C labeled proteins in D₂O and dilute liquid crystals with minimal spectral crowding. The presented experiments are especially suitable for small or medium sized proline-rich proteins, or proteins that require high pH solvent conditions, making ¹H^N detected experiments unattractive. In addition, the tetrahedral coordination of C is superior to the planar peptide bond for determination of local alignments in partially structured polypeptides. For the efficient use of spectrometer time and to avoid complications arising from the varying magnitude of the alignment tensor during relatively long experiments, the and couplings can also be measured simultaneously in an E.COSY like manner with high accuracy. The pulse sequences are balanced for cross-correlation effects and minimized for relaxation losses. The pulse sequences are tested with a sample of ¹⁵N/¹³C human ubiquitin. We find internuclear vector directions determined from the dipolar couplings to have an excellent correlation with those of ubiquitins refined solution structure.     

Phosphorus concentration in sediment, water and tissues of␣three submerged macrophytes of Myall Lake, Australia

Phosphorus content in sediment, water and tissues of three macrophyte species growing in Myall Lake, Australia were studied from January to November, 2004. The sites investigated were North–West (NW), North–East (NE), South–West (SW) bays and Central deep area of the lake (CL). The objective of this study was to investigate how total phosphorus (TP) in plant tissues relate to phosphorus pools and the role played by the aquatic macrophyte species under investigation in phosphorus recycling in the lake. Of the four investigated sites of the lake, TP in plant tissues were significantly higher in North–West and South–West bays compared to the rest. Najas marina had significantly higher TP content (e.g., 1.55 and 1.44 mg/g dw.; P < 0.05) for NW and SW respectively, than the other two species. N. marina is a rooted macrophyte while charophytes (C. fibrosa and Nitella hyalina) are pseudo-rooted macrophytes. Total phosphorus in the sediment and water column were significantly higher in Central deep area of the lake compared to the other three bays (P < 0.05, n 5). Soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) in sediment pore water correlated significantly with phosphorus content in the tissue of N. marina ( ; ) as well as TP in sediment (␣ and ). Using the two-compartmental uptake model, it was observed that, sediment was the main compartment through which Ni. hyalina obtained phosphorus while for the other two species, water column was the uptake route for the phosphorus. These correlations suggest that, water column and sediments are important pathways for phosphorus uptake in plants.     

Immobilization of the recombinant invertase INVB from <Emphasis Type="Italic">Zymomonas mobilis</Emphasis> on Nylon-6

The recombinant invertase INVB (re-INVB) from Zymomonas mobilis was immobilized on microbeads of Nylon-6, by means of covalent bonding. The enzyme was strongly and successfully bound to the support. The activity of the free and immobilized enzyme was determined, using 10% (w/v) sucrose, at a temperature ranging between 15 and 60 °C and a pH ranging between 3.5 and 7. The optimal pH and temperature for the immobilized enzyme were 5.5 and 25 °C, respectively. Immobilization of re-INVB on Nylon-6 showed no significant change in the optimal pH, but a difference in the optimal temperature was evident, as that for the free enzyme was shown to be 40 °C. The values for kinetic parameters were determined as: 984 and 98 mM for of immobilized and free re-INVB, respectively. values for immobilized and free enzymes were 6.1 × 10² and 1.2 × 10⁴ s⁻¹, respectively, and immobilized re-INVB showed of 158.73 μmol h min⁻¹ mg⁻¹. Immobilization of re-INVB on Nylon-6 enhanced the thermostability of the enzyme by 50% at 30 °C and 70% at 40 °C, when compared to the free enzyme. The immobilization system reported here may have future biotechnological applications, owing to the simplicity of the immobilization technique, the strong binding of re-INVB to the support and the effective thermostability of the enzyme.