A kinetic study on the copper-albumin catalyzed oxidation of ascorbate

Serum albumin can specifically bind one Cu(II)-ion, and is proposed to function as a copper transport protein in vivo. Cu(II)-albumin is rapidly reduced by ascorbate. A second order rate constant of 0.54 mM^–1 min^–1 was estimated for the reaction. The oxidation process is catalytic, the Cu(I)-albumin molecule being reoxidized by molecular oxygen. The reaction was found to follow Michaelis-Menten kinetics, characterized by an apparent K_m-value of 0.89 mM, and a catalytic constant of 0.066 M O₂/min. An apparent inhibition of oxygen uptake was obtained with catalase (but not with superoxide dismutase), suggesting the formation of H₂O₂ in the system. Wilson's disease patients usually have increased amounts of non-ceruloplasmin copper in plasma. The low level of plasma ascorbate observed in such patients could possibly be due, at least in part, to an oxidation by Cu(II)-albumin.     

Opioid receptor binding in rat spinal cord

The interaction of various radioligands with spinal opioid receptors has been characterized under variable experimental conditions. Binding to , , and sites was measured in all (cervical, thoracic, lumbar) segments. The apparent affinity constant (K) of [³H]Ethylketocyclazocine (EKC) was similar in Tris, 2.09 (±1.06)×10⁸ M^–1, and phosphate buffer, 2.16 (±0.02)×10⁸ M^–1, when its interaction with and sites was blocked. Without blocking ligands, EKC binding was resolved in two components:K ₁=1.01 (±0.21)×10⁹ M^–1 andK ₂=0.95 (±0.61)×10⁷ M^–1. Likewise, the binding of [D-Ala², MePhe⁴, Gly(ol)⁵]enkephalin (DAGO) or [D-Ala², D-Leu⁵]-enkephalin (DADLE) alone was represented by a 2-site model. By adjusting the radioligand and receptor concentration or by the addition of blocking ligands, binding was represented by a 1-site model for DAGO,K=4.35 (±1.41)×10⁸ M^–1, and DADLE,K=2.44 (±0.08)×10⁸ M^–1.The abbreviations used are DADLE [D-Ala², D-Leu⁵]enkephalin - DAGO [D-Ala², MePhe⁴, Gly(ol)⁵]enkephalin - EKC ethylketocyclazocine - DYN dynorphin (1–17)     

Human serum albumin coordinates Cu(II) at its N-terminal binding site with 1 pM affinity

The conditional stability constant at pH 7.4 for Cu(II) binding at the N-terminal site (NTS) of human serum albumin (HSA) was determined directly by competitive UV–vis spectroscopy titrations using nitrilotriacetic acid (NTA) as the competitor in 100 mM NaCl and 100 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (Hepes). The log K _NTS^c value of 12.0 ± 0.1 was determined for HSA dissolved in 100 mM NaCl. A false log log K _NTS^c value of 11.4 ± 0.1 was obtained in the 100 mM Hepes buffer, owing to the formation of a ternary Cu(NTA)(Hepes) complex. The impact of the picomolar affinity of HSA for Cu(II) on the availability of these ions in neurodegenerative disorders is briefly discussed.     

Analysis of ligand-binding to the kringle 4 fragment from human plasminogen

The interaction of the isolated human plasminogen kringle 4 with the four -amino acid ligands -aminocaproic acid (ACA), N-acetyl-l-lysine (AcLys), trans-aminomethyl(cyclohexane)carboxylic acid (AMCHA) and p-benzylaminesulfonic acid (BASA) has been further characterized by ¹H-NMR spectroscopy at 300 and 600 MHz. Pronounced high-field shifts, reaching 3 ppm, are observed for AMCHA resonances upon binding to kringle 4, which underscores the relevance of ligand lipophilic interactions with aromatic side chains at the binding site. Ligand titration curves for the nine His and Trp singlets found in the kringle 4 aromatic spectrum reveal a striking uniformity in the kringle response to the various ligands. The average binding curves exhibit a clear Langmuir absorption isotherm saturation profile and the data were analyzed under the assumption of one (high affinity) binding site per kringle. Equilibrium association constants (K _a ) and first order dissociation rate constants (k _off) were derived from linearized expressions of the Langmuir isotherm and of the spectral line-shapes, respectively. The results for the four ligands, at 295 K, pH^* 7.2, indicate that: (a) AMCHA exhibits the strongest binding (K _a =159 mM ^-1) and ACA the weakest (K _a =21 mM ^–1) with AcLys and BASA falling in between; (b) ACA dissociates readily (k _off = 5.3 × 10³ s^–1) and AMCHA associates the fastest (k _off = 2.0 × 10⁸ M ^–1 s^–1) while the kinetics for BASA exchange is relatively slow (k _off = 0.8 × 10³ s^–1, k _on = 0.6 × 10⁸ M ^–1s^–1); (c) the ligand-binding kinetics is close to diffussion-controlled.Abbreviations ACA -aminocaproic acid - AcLys N-acetyl-l-lysine - AMCHA t-aminomethyl(cyclohexane)carboxylic acid - BASA p-benzylaminesulfonic acid - K4 kringle 4 - NOE nuclear Overhauser effect - ppm parts-per-million - pH^* glass electrode pH reading uncorrected for deuterium isotope effects - K _a ligand-kringle 4 equilibrium association constant - k _off ligand-kringle 4 dissociation rate constant - k _on ligand-kringle 4 association rate constant     

Microcalorimetric study of magnesium-adenosine triphosphate ternary complex

Using an original microcalorimetric method, the existence of the Mg₂ATP ternary chelate has been studied. The thermodynamic parameters of this complex are H=7.2±0.5 kJ mole^–1 andK=49±9 M^–1. These values are compared with those previously obtained for binary chelate Mg ATP^2–. A possible regulation role of Mg₂ATP is discussed.     

Effect of light intensity and ammonium-N on carotenogenesis ofTrentepohlia odorata andDunaliella bardawil

AxenicTrentepohlia odorata was cultured at three different NH₄Cl levels (3.5 × 10^–2, 3.5 × 10^–3, 3.5 × 10^–4 M) and three different light intensities (48, 76, 122 µmol m^–2 s^–1). Chloride had no effect on growth over this range of concentration. High light intensity and high NH₄Cl concentration enhanced the specific growth rate. The carotenoid content increased under a combination of high light intensity and low N concentration. WhenD. bardawil was exposed to the same combination of growth conditions, there was an increase in its carotenoid content. The light saturation and the light inhibition constants (K _s andK _i, respectively) for growth, and the saturation constant (K _m) for NH₄Cl were determined. TheK _s andK _i values were higher inT. odorata (66.7 and> 122 mol m^–2 s^–1, respectively) than inD. bardawil (5.1 and 14.7 µmol m^–2 s^–1, respectively). TheK _m value determined at 122 µmol m^–2 s^–1, however, was lower inT. odorata (0.048 µM) than inD. bardawil (0.062 µM).Author for correspondence     

Interaction of Perch Fucolectin with Lewis Antigens

The interaction of fucolectin of perch Perca fluviatilis (PFL) with a set of Lewis antigens was studied by monitoring changes in its tryptophan fluorescence. PFL bound Le^c (H type 1)-pentasaccharide (K _a = 6.6 × 10^{3 –1}) and H type 6-trisaccharide (K _a = 2.5 × 10^{3 –1}); bound, although less strongly, with Le^b-hexasaccharide (K _a = 4.0 × 10^{2 –1}); and failed to interact with Le^a-, Le^x-, and Le^d-containing oligosaccharides. PFL belongs to a new type of the fucolectins recognizing H-disaccharide Fuc1-2Gal within various antigens, including H type 1/2 and Le^b.     

The 40s Ω-loop plays a critical role in the stability and the alkaline conformational transition of cytochrome<Emphasis Type="Italic"> c</Emphasis>

The structural and redox properties of a non-covalent complex reconstituted upon mixing two non-contiguous fragments of horse cytochrome c, the residues 1–38 heme-containing N-fragment with the residues 57–104 C-fragment, have been investigated. With respect to native cyt c, the complex lacks a segment of 18 residues, corresponding, in the native protein, to an omega ()-loop region. The fragment complex shows compact structure, native-like -helix content but a less rigid atomic packing and reduced stability with respect to the native protein. Structural heterogeneity is observed at pH 7.0, involving formation of an axially misligated low-spin species and consequent partial displacement of Met80 from the sixth coordination position of the heme-iron. Spectroscopic data suggest that a lysine (located in the Met80-containing loop, namely Lys72, Lys73, or Lys79) replaces the methionine residue. The residues 1–38/57–104 fragment complex shows an unusual biphasic alkaline titration characterized by a low (pK_a1=6.72) and a high pK_a-associated state transition (pK_a2=8.56); this behavior differs from that of native cyt c, which shows a monophasic alkaline transition (pK_a=8.9). The data indicate that the 40s -loop plays an important role in the stability of cyt c and in ensuring a correct alkaline conformational transition of the protein.     

Spectroscopic and binding studies of azide to type-2-copper-depleted ascorbate oxidase from zucchini

Summary Binding of azide to type-2-copper-depleted (T2D) zucchini ascorbate oxidase, containing reduced type-3 Cu centers, and met-T2D ascorbate oxidase, containing oxidized type-3 Cu centers, has been studied spectroscopically. In both cases titration with azide in 0.1 M phosphate pH 6.8 produces a broad near-ultraviolet band with maximum at 455 nm (e 2500 M^–1 cm^–1, with respect to the met-T2D enzyme) and shoulder at 390 nm (e 1700 M^–1 cm^–1), that are assigned to(azide)Cu(II) ligand-to-metal charge transfer (LMCT) transitions. This is accompanied by a reduction of absorbance at 330 nm in the met-T2D) enzyme adduct (e –1400 M^–1 cm^–1). A broad circular dichroic band of negative sign between 370–480 nm corresponds to the LMCT absorption band. Analysis of the titration data indicates that one azide ion binds independently to each of the binuclear T3 Cu couples with low affinity (K = 50 M^–1). The ESR signal of the T1 Cu observed in frozen solutions of the T2D enzyme is also perturbed by the addition of azide. The analogies in the azide-binding characteristics between ascorbate oxidase and laccase are discussed.     

Using a chelate-buffered nutrient solution to establish the critical solution activity of Mn2+ required by barley (Hordeum vulgare L.)

Relatively little is known about the responses of plants to micronutrients when these nutrients are maintained at the very low levels found in soils of low fertility. We have determined the requirement of barley (Hordeum vulgare L. cv Herta) for ionic Mn²⁺ in plant culture solutions using the chelating agent HEDTA as a buffer for micronutrient metal ions. The chemical activity of Mn²⁺ was varied approximately 10,000-fold from log(Mn²⁺)=–10.8 to –6.8 (pMn 10.8 to pMn 6.8), while holding constant the activities of the other micronutrient cations. Growth, appearance, and composition of Herta barley indicated that log(Mn²⁺) of approximately –8.3 would permit optimal dry matter production and normal plant development. The specific accumulation rate of Mn by 15 to 23 day old seedlings was a linear function of the Mn²⁺ activity in solution. At log(Mn²⁺) of about –9.8 or below, barley seedlings were unable to accumulate significant amounts of Mn, and at some harvests, suffered a net loss of Mn to solution. Seedlings younger than 11 days old were ineffective accumulators of several cations, including Mn, Fe, Zn, Cu, Mg, and Ca. Differences in Mn availability did not influence uptake of other cations, except that Cu uptake by roots increased with increasing Mn uptake.Abbreviations MES 2-(N-morpholino)-ethanesulphonic acid - HEDTA N-(2-hydroxyethyl)ethylene-dinitrilotriacetic acid - DTPA diethylenetrinitrilopentaacetic acid     

Ethanol acetylation by mycelium-bound carboxylesterase of Aspergillus oryzae: estimation of thermodynamic parameters and integral productivity

The results collected at different temperatures for ethanol acetylation by cell-bound carboxylesterase from lyophilized cells of Aspergillus oryzae have been used to investigate the kinetics and thermodynamics of this esterification in n-heptane. The occurrence of reversible unfolding followed by irreversible denaturation of the enzyme has been proposed to explain the increase in the starting rate of ethyl acetate formation with temperature observed up to 55 °C and the consequent fall beyond this threshold. The Arrhenius model has been used to estimate the apparent activation enthalpies of both the acetylation reaction (H = 29–33 kJ mol^–1) and reversible enzyme unfolding (H _u = 56–63 kJ mol^–1). The results of residual activity tests performed with cells previously exposed at different temperatures for variable times enabled us also to estimate the first-order rate constant of irreversible denaturation (2.40 × 10^–3 h^–1 < k _d < 8.11 × 10^–3 h^–1) as well as the related thermodynamic parameters (H _d = 22 kJ mol^–1; S _d = –0.29 kJ mol^–1 K^–1). This last phenomenon proved particularly slow for the system under consideration, probably because the biocatalyst link to the mycelium was able to improve its thermostability. In view of future continuous application, the effects of operating time, starting substrate concentration and temperature on the theoretical integral productivity of a fixed-bed column filled with this biocatalyst have been investigated.     

Therlt11 andraec1 mutants ofArabidopsis thaliana lack the activity of a basic-amino-acid transporter

The concentration dependence of the influx ofl-lysine in excised roots ofArabidopsis thaliana seedlings was analyzed for the wild-type (WT) and two mutants,rlt11 andraec1, which had been selected as resistant to lysine plus threonine, and to S-2-aminoethyl-l-cysteine, respectively. In the WT three components were resolved: (i) a high-affinity, low-capacity component [K _m = 2.2 M;V _max = 23 nmol·(g FW)^–1·h^–1]; (ii) a low-affinity, high-capacity component [K _m = 159 M;V _max = 742 nmol·(g FW)^–1·h^–1]; (iii) a component which is proportional to the external concentration, with a constant of proportionalityk = 104 nmol·(g FW)^–1 h^–1];·mM^–1. The influx ofl-lysine in the mutants was lower than in the WT, notably in the concentration range 0.1–0.4 mM, where it was only 7% of that in the WT. In both mutants the reduced influx could be fully attributed to the absence of the low-affinity (high-K _m ) component. This component most likely represents the activity of a specific basic-amino-acid transporter, since it was inhibited by several other basic amino acids (arginine, ornithine, hydroxylysine, aminoethylcysteine) but not byl-valine. The high-affinity uptake ofl-lysine may be due to the activity of at least two general amino acid transporters, as it was inhibitable byl-valine, and could be further dissected into two components with a high affinity (K _i = 1–5 M; and a low affinity (K _i = 0.5–1mM) forl-valine, respectively. Therlt11 andraecl mutant have the same phenotype and the corresponding loci were mapped on chromosome 1, but it is not yet clear whether they are allelic.Abbreviations AEC S-2-aminoethyl-l-cysteine - K _i equilibrium constant - WT wild-type     

Intraparticle mass-transfer resistance and apparent time stability of immobilized yeast alcohol dehydrogenase

The stability and, consequently, the lifetime of immobilized enzymes (IME) are important factors in practical applications of IME, especially so far as design and operation of the enzyme reactors are concerned. In this paper a model is presented which describes the effect of intraparticle diffusion on time stability behaviour of IME, and which has been verified experimentally by the two-substrate enzymic reaction. As a model reaction the ethanol oxidation catalysed by immobilized yeast alcohol dehydrogenase was chosen. The reaction was performed in the batch-recycle reactor at 303 K and pH-value 8.9, under the conditions of high ethanol concentration and low coenzyme (NAD⁺) concentration, so that NAD⁺ was the limiting substrate. The values of the apparent and intrinsic deactivation constant as well as the apparent relative lifetime of the enzyme were calculated.The results show that the diffusional resistance influences the time stability of the IME catalyst and that IME appears to be more stabilized under the larger diffusion resistance.List of Symbols C _A, C_B, C_E mol · m^–3 concentration of coenzyme NAD⁺, ethanol and enzyme, respectively - C _p mol · m³ concentration of reaction product NADH - d _p mm particle diameter - D _eff m² · s^–1 effective volume diffusivity of NAD⁺ within porous matrix - k _d s^–1 intrinsic deactivation constant - K _A, K_A, K_B mol · m^–3 kinetic constant defined by Eq. (1) - K _A ^x mol · m^–3 kinetic constant defined by Eq. (5) - r _A mol · m^–3 · s^–1 intrinsic reaction rate - R m particle radius - R _v mol · m^–3 · s^–1 observed reaction rate per unit volume of immobilized enzyme - t _E s enzyme deactivation time - t _r s reaction time - V mol · m^–3 · s^–1 maximum reaction rate in Eq. (1) - V ^x mol · m^–3 · s^–1 parameter defined by Eq. (4) - V _f m³ total volume of fluid in reactor - w _s kg mass of immobilized enzyme bed - factor defined by Eqs. (19) and (20) - kg · m^–3 density of immobilized enzyme bed - unstableness factor - effectiveness factor - Thiele modulus - relative half-lifetime of immobilized enzyme Index o values obtained with fresh immobilized enzyme     

Complexation of oxoanions and cationic metals by the biscatecholate siderophore azotochelin

Azotochelin is a biscatecholate siderophore produced by the nitrogen-fixing soil bacterium Azotobacter vinelandii. The complexation properties of azotochelin with a series of oxoanions [Mo(VI), W(VI) and V(V)] and divalent cations [Cu(II), Zn(II), Co(II) and Mn(II)] were investigated by potentiometry, UV–vis and X-ray spectroscopy. Azotochelin forms a strong 1:1 complex with molybdate (log K = 7.6 ± 0.4) and with tungstate and vanadate; the stability of the complexes increases in the order Mo < V < W (log K _app^Mo = 7.3 ± 0.4; log K _app^V = 8.8 ± 0.4 and log K _app^W = 9.0 ± 0.4 at pH 6.6). The Mo atom in the 1:1 Mo–azotochelin complex is bound to two oxo groups in a cis position and to the two catecholate groups of azotochelin, resulting in a slightly distorted octahedral configuration. Below pH 5, azotochelin appears to form polynuclear complexes with Mo in addition to the 1:1 complex. Azotochelin also forms strong complexes with divalent metals. Of the metals studied, Cu(II) binds most strongly to azotochelin , followed by Zn(II) , Mn(II) and Co(II) . Since very few organic ligands are known to bind strongly to oxoanions (and particularly molybdate) at circumneutral pH, the unusual properties of azotochelin may be used for the separation and concentration of oxoanions in the laboratory and in the field. In addition, azotochelin may prove useful for the investigation of the biogeochemistry of Mo, W and V in aquatic and terrestrial systems. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Fatty acid-binding to erythrocyte ghost membranes and transmembrane movement

Summary Palmitate binding to human erythrocyte ghost membranes has been investigated with ghost preparations suspended in 0.2% albumin solutions. Free unbound palmitate in the extracellular water phase was measured in equilibrium studies using albumin-filled acid loaded ghosts as small semipermeable bags. The apparent dissociation constant of binding to the membrane is 13.5 nM and the binding capacity 19 nmoles per 7.2 × 109 cells.The 0°C exchange efflux kinetics of palmitate from albumin-filled ghosts is described by a model, which provides estimates of the rate constant of membrane transfer, k₃ = 0.024 s^–1, independent of the molar ratio of palmitate to albumin () and of a mean dissociation rate constant of the palmitate-albumin complex, k₁ = 0.0015 s^–1 at 0.2, allowing for a heterogeneity of the palmitate binding to albumin.The values of a third kinetically determined dependent model constant, Q, the ratio of palmitate bound to the membrane inner surface to palmitate on intracellular albumin, are not different from the Q values obtained by equilibrium experiments.The temperature dependences of k₁ and k₃ in the interval 0°C to 15°C give activation energies of 96 and 103 kJ/mole, respectively. The 0°C exchange efflux increases about 2 fold in response to a rise of pH from 6 to 9. The results suggest a carrier mediated palmitate flux at low with a V_max about 2 pmoles min^–1 cm^–2 at 0°C pH 7.3.     

Water and salt permeability of gastric vesicles

Summary Volume-dependent changes in light scatter have been shown to be a linear function of the osmotic gradient imposed upon gastric vesicles purified from hog gastric mucosa. Observation of the light scattered 90° to incident, using the Durrum stop flow system D-110, indicates that the vesicles exposed to hypertonic medium undergo rapid shrinkage due to water loss from the vesicle interior. The rate constant for this water movement is 1.1±0.09 sec^–1 (n=10) and is linearly dependent on temperature between 16 and 36°C. The activation energy of 13.93±0.60 kcal mole^–1 (n=3), calculated from an Arrhenius plot, is inconsistent with water movement facilitated by a large-pore aqueous channel. A slower reswell phase, dependent on solute entry into the intravesicular space, follows the water-dependent shrink phase. KCl entry, studied because of the intravesicular requirement for active K⁺/H⁺ transport, exhibits two entry stages. The faster, described by a single exponential imposed upon a constantly sloping background, has a rate constant of 7.75±0.48×10^–3 sec^–1 (n=15). The slower phase, which typically accounts for 90% of the reswell process, demonstrates a rate constant of 1.94±0.23×10^–4 sec^–1 (n=15). In the presence of valinomycin or nigericin, two fast rate constants and one slow rate constant of swelling are observed. The rate constant of the faster reswell phase is increased from 7.75±0.48×10^–3 sec^–1 (n=15) to 15.74±3.7×10^–3 sec^–1 (n=5) and 17.23±3.4×10^–3 (n=3) by the addition of nigericin (1 g ml^–1) and valinomycin (4.5 m), respectively. The second part of the faster reswell phase is approximately that seen in the control population. Transport-dependent volume changes of significant magnitude can be demonstrated following the addition of ATP to vesicles equilibrated with 150mm KCl. The volume change is a function of HCl leak rate and is abolished by ionophores which eliminate the transport-dependent pH gradient. So ₄ ^–- substitution, which eliminates the overshoot phenomena observed in KCl medium, also eliminates the shrinkage resulting from ATP addition.     

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo

Summary The function of the caecal bulb, and its adaptation to chronic high- or low-Na⁺ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 g·kg^–1 body mass) were also measured.Evidence was found for primary active net absorption of Na⁺, inducing parallel Na-linked absorption of water and Cl^– and secretion of K⁺. Around 20–35% of total Cl^– absorption and K⁺ secretion were independent of Na⁺ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3×10^–3 (G _Cl) and 1.1×10^–3 (G _K) S·cm^–2.Acetate (40mM) stimulated Na⁺ fluxes (8.5–9.9 Eq·cm^–2·h^–1) and Na-linked water fluxes (27–44 l·cm^–2·h^–1). Increased coupling ratios (2.9–4.6 l·Eq^–1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway.Low-Na⁺ maintenance enhanced EPD (49–69 mV, serosa positive) and all net fluxes:J _Na (6.8–11.6);J _K (–3.2––4.3);J _Cl (4.3–5.6 Eq·cm serosal area^–2·h^–1);J _v (28–43 l·cm^–2·h^–1) (mucosal-serosal fluxes positive).Acute aldosterone enhancedJ _Na (10.8–14.0 Eq·cm^–2·h^–1) and EPD (54–66 mV) by 3 h after injection, but had no effect on the Na-linked components ofJ _K orJ _Cl.Abbreviations ECPD, EPD Electrochemical or electrical potential difference - G _Cl ,G _K ionic conductances (Cl^–, K⁺) - J _v ,J _ion net volume or ion flux rate, mucosa-serosa positive;P _d (Cl) diffusive permeability coefficient (of Cl^–) - SEDM standard error of difference between means     

Integral kinetics of the cleavage of maltose catalysed by α-glucosidase fromSaccharomyces carlsbergensis

Summary A new, sensitive and continuous assay for -glucosidase is described exploiting the different angles of rotation for the substrate maltose and the product glucose. Kinetic experiments revealed a very pronounced product inhibition of -glucosidase fromSaccharomyces carlsbergensis with a K_i of 4.85·10^–3 M for glucose.The K_M of maltose was found to be 37.8·10^–3 M. Taking these values, an integral kinetic curve for the enzymatic hydrolysis of maltose was calculated, which is shown to fit the experimental data.Symbols used k₁ (min^–1) pseudo first-order rate constant (for enzymatic cleavage) - k₂ (min^–1) rate constant (for mutarotation reaction) - I, P (mol/1) inhibitor (product) concentration - k_i (mmol/1) inhibitor constant - K_M (mmol/l) Michaelis constant - [M] ₅₈₉ ³⁰ (degree/m · l/mol) molecular rotation at 30°C and 589 nm - s (mmol/l) substrate concentration - R (mmol/mg · min) reaction rate - V_max (mmol/mg · min) maximal rate - U (mol/min) activity unit (here at 30°C and pH=6.8) Indices O initial value - max maximal value     

Technical communication: Determination of cuprous ions in bacterial leachates and for environmental monitoring

A sensitive and precise spectrophotometric method has been developed for the determination of copper(I) in bacterial leach liquors produced by the action of Thiobacillus ferrooxidans and T. thiooxidans on copper ores. In this method bicinchoninic acid (BCA) has been used as the chromogenic reagent which produces a stable purple complex with Cu(I) which was found to obey Beer's Law and with _max at 560 nm. The coloured complex has a molar extinction coefficient () value of 6.6 × 10³ l mol^–1 cm^–1; specific absorptivity () value of 0.104 ml^–1 g cm^–1 and the Sandell sensitivity (S) value was 0.0096 g cm². Optimal conditions for development of coloration/sensitivity were determined. Interferences due to cations and anions were investigated and various masking agents for alleviating their inhibition were studied. The method has been found very useful in determining ratios of Cu(I) to Cu(II) in bacterial leach liquors and should play a significant role in determining the reaction mechanisms of biological leaching and for environmental monitoring.     

Comparison of plant uptake and plant toxicity of various ions in wheat

The effects of varying solution concentrations of manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga) and lanthanum (La) on plant chemical concentrations, plant uptake and plant toxicity were determined in wheat (Triticum aestivum L.) grown in a low ionic strength (2.7×10^–3 M solution culture). Increasing the solution concentration of Mn, Zn, Cu, B, Fe, Ga and La increased plant concentrations of that ion. Asymptotic maximum plant concentrations were reached for Zn (10 mg kg DM^–1 in the roots), Ga (2 mg kg DM^–1 in the tops and 18 mg kg DM^–1 in the roots) and La (0.4 mg kg DM^–1 in the tops and 4 mg kg DM^–1 in the roots). Plant ion concentrations were, on average, 3 times higher in the roots than the tops for Mn and Zn, 7 times for Cu, 9 times for Fe, 12 times for Ga and 15 times for La. In contrast, B concentrations were higher in the tops than the roots by, on average, 2 times. The estimated toxicity threshold (plant concentration at which a rapid decrease in yield occurred) in the tops was 0.4 mg g DM^–1 for B, 2 for Zn, 0.075 for Cu and 0.09 for La and in the roots 0.2 mg g DM^–1 for B, 5 for Zn, 0.3 for Cu and 3 for La. Plant uptake rates of the ions (as estimated by the slope of the relationship between solution ion concentrations and plant ion concentrations) was in the order B 250 mg kg DM^–1 M ^–1). Plant toxicity was estimated as the reciprocal of the plant concentration that reduced yield by 50% (change in relative yield per mg ion kg DM^–1). The plant toxicity of the ions tested was in the order Mn相似文献