The kinetics of cyanide binding by human erythrocyte catalase

The kinetics of the binding reaction of cyanide by human erythrocyte catalase at 25 °C has been studied over the pH range 4.2 to 10.2 by means of temperature jump and stopped flow techniques. Catalase reacts with cyanide at a constant rate in the range pH 4.2 to 8.1 which decreases at higher pH. This is most simply explained by the reaction of catalase with unionized hydrogen cyanide molecules. The pH-independent rate constant for the formation of the catalase-cyanide complex is (1.3 ± 0.1) × 10⁶m^?1 s^?1. The association equilibrium constant and the dissociation rate constant for the catalase-cyanide complex were determined from the relaxation amplitudes of temperature jump experiments and by spectrophotometric titration and are (3.1 ± 0.2) × 10⁵m^?1 and 4.2 ± 0.6 s^?1, respectively in the pH-independent region.     

Salt tolerance in suspension cultures of sugar beet : induction of na/h antiport activity at the tonoplast by growth in salt

Cell suspension cultures of sugar beet were grown at various salinities (0-200 millimolar NaCl). Their tolerance to Na⁺ was comparable to that of the intact plant. Tonoplast vesicles were prepared by sucrose density gradient centrifugation of microsomal membranes and shown to be highly purified. The vesicles were subjected to a pH jump in the presence of acridine orange and the rate of recovery of fluorescence after addition of Na⁺ was used as a measure of Na⁺-dependent H⁺ efflux. In the presence of K⁺ and valinomycin, the Na⁺/H⁺ antiport showed saturation kinetics. Increasing Na⁺ in the growth medium did not change the apparent K_m for Na⁺, but increased V_max to about twice the control value, suggesting a specific induction of antiport synthesis by salt.     

Continuous fermentation to produce fungal protein. Effect of growth rate on the biomass yield and chemical composition of Fusarium moniliforme

Fusarium moniliforme was grown on a carob aqueous extract in a chemostat for fungal protein production. The substrate was adjusted to provide 0.5% carob sugars supplemented with inorganic salts. The dilution rate varied from 0.086 to 0.227 hr^?1 under constant conditions of temperature (30°C), pH (4.5), and oxygen saturation (60–80%). A yield of 0.709 g dry mycelium/g consumed carob sugar and a productivity value of 0.687 g dry mycelium/liter hr^?1 were obtained at μ = 0.205 hr^?1. The maintenance coefficient was 0.077 g carob sugar/g dry mycelium hr^?1. While the carbohydrate and purine content of dry mycelium increased at μ values from 0.114 to 0.205 hr^?1 both true (Lowry) and crude (N × 6.25) protein contents decreased at the same μ range. Maximum values of 36.3% true and 47.9% crude protein of dry mycelium were obtained at μ = 0.114 hr^?1, whereas a minimum purine content of 99.8 μmol/g corresponding to 6.42% nucleic acids was recorded at μ = 0.086 hr^?1. It was concluded that a continuous fermentation of carob aqueous extract using F. moniliforme should be operated at growth rates of approximately 0.205 hr^?1 in order to maximize protein production.     

Bacillus mojavensis strain 32A, a bioflocculant-producing bacterium isolated from an Egyptian salt production pond

Bacillus mojavensis strain 32A that exhibited 96.11% flocculation efficiency for clay suspensions was selected from other 15 comparative strains. Under growth condition, strain 32A was able to produce 5.2 g/L of purified biopolymer. Its constituent was mainly polysaccharide and protein with proportional of 98.4-1.6% respectively. FTIR spectrum was confirming its chemical analysis. This biopolymer attain very fast sedimentation rate. The cost-effective biopolymer and CaCl₂ dosages were 3 mg/L and 5 ml/L respectively that posed 89.7% flocculation efficiency. These dosages were suitable only for clay concentrations ?5 g/L. The maximum flocculation efficiency of the biopolymer recorded at pH 1.0 of clay suspension. The too high (>75 °C) or too low (<25 °C) clay suspension temperature was unfavorable for the biopolymer flocculation performance. The biopolymer solution utilized high thermal stability over the temperature range of 5-60 °C. Furthermore, its pH stability recorded at pH range of 5-9.     

K+ transport in mitoplasts

K⁺ transport into mitoplasts, prepared by digitonin disruption and removal of the outer membranes from rat liver mitochondria, has been studied. Unidirectional K⁺ influx has been measured by means of ⁴²K, in the presence of the respiratory substrate succinate. K⁺ influx is inhibited by CN^?, antimycin A and dicyclohexylcarbodiimide, but is insensitive to oligomycin. A linear dependence of the reciprocal of the K⁺-influx rate on the reciprocal of the external K⁺ concentration is observed. Under the conditions studied, the apparent K_m for K⁺ of the transport mechanism is approx. 6 mM, while the V_max of K⁺ influx is approx. 5 μ mol K⁺/g protein per min. The rate of K⁺ influx increases with increasing external pH over the range from 6.8 to 8.0. The observed kinetics, pH dependence and inhibitor sensitivity are essentially similar to previously reported characteristics of K⁺ transport into intact rat liver mitochondria. It is concluded that the outer mitochondrial membrane does not have a role in controlling K⁺ flux into rat liver mitochondria.     

Native-State Heterogeneity of β2-Microglobulin as Revealed by Kinetic Folding and Real-Time NMR Experiments

The kinetic folding of β₂-microglobulin from the acid-denatured state was investigated by interrupted-unfolding and interrupted-refolding experiments using stopped-flow double-jump techniques. In the interrupted unfolding, we first unfolded the protein by a pH jump from pH 7.5 to pH 2.0, and the kinetic refolding assay was carried out by the reverse pH jump by monitoring tryptophan fluorescence. Similarly, in the interrupted refolding, we first refolded the protein by a pH jump from pH 2.0 to pH 7.5 and used a guanidine hydrochloride (GdnHCl) concentration jump as well as the reverse pH jump as unfolding assays. Based on these experiments, the folding is represented by a parallel-pathway model, in which the molecule with the correct Pro32 cis isomer refolds rapidly with a rate constant of 5–6 s^? 1, while the molecule with the Pro32 trans isomer refolds more slowly (pH 7.5 and 25 °C). At the last step of folding, the native-like trans conformer produced on the latter pathway isomerizes very slowly (0.001–0.002 s^? 1) into the native cis conformer. In the GdnHCl-induced unfolding assays in the interrupted refolding, the native-like trans conformer unfolded remarkably faster than the native cis conformer, and the direct GdnHCl-induced unfolding was also biphasic, indicating that the native-like trans conformer is populated at a significant level under the native condition. The one-dimensional NMR and the real-time NMR experiments of refolding further indicated that the population of the trans conformer increases up to 7–9% under a more physiological condition (pH 7.5 and 37 °C).     

Sugar uptake and starch biosynthesis by slices of developing maize endosperm

¹⁴C-Sugar uptake and incorporation into starch by slices of developing maize (Zea mays L.) endosperm were examined and compared with sugar uptake by maize endosperm-derived suspension cultures. Rates of sucrose, fructose, and d- and l-glucose uptake by slices were similar, whereas uptake rates for these sugars differed greatly in suspension cultures. Concentration dependence of sucrose, fructose, and d-glucose uptake was biphasic (consisting of linear plus saturable components) with suspension cultures but linear with slices. These and other differences suggest that endosperm slices are freely permeable to sugars. After diffusion into the slices, sugars were metabolized and incorporated into starch. Starch synthesis, but not sugar accumulation, was greatly reduced by 2.5 millimolar p-chloromercuribenzenesulfonic acid and 0.1 millimolar carbonyl cyanide m-chlorophenylhydrazone. Starch synthesis was dependent on kernel age and incubation temperature, but not on external pH (5 through 8). Competing sugars generally did not affect the distribution of ¹⁴C among the soluble sugars extracted from endosperm slices incubated in ¹⁴C-sugars. Competing hexoses reduced the incorporation of ¹⁴C into starch, but competing sucrose did not, suggesting that sucrose is not a necessary intermediate in starch biosynthesis. The bidirectional permeability of endosperm slices to sugars makes the characterization of sugar transport into endosperm slices impossible, however the model system is useful for experiments dealing with starch biosynthesis which occurs in the metabolically active tissue.     

pH and thermal stability studies of chitinase from Trichoderma harzianum: A thermodynamic consideration

The combined effect of pH and temperature on chitinase was investigated using response surface methodology. A central composite design for two variables was employed. The optimal pH and temperature for the least degree of deactivation were found out to be 5.4 and 24°C respectively. The deactivation rate constants and the half life of chitinase were estimated at different pH and temperature combinations. At the optimal pH of 5.4, the rate of the deactivation was found to be the least. Thermodynamic parameters, viz., ΔH^*, ΔS^*, ΔG^* and activation energy of thermal deactivation of chitinase were calculated in the temperature range from 50°C to 60°C.     

The binding of Ni2+ to adenylyl-3',5'-adenosine and to poly(adenylic acid)

Studies of the binding of Ni²⁺ to adenylyl-3',5'-adenosine (ApA) at pH 6-0 by ultraviolet spectrophotometry indicate the formation of a 1:1 complex in the presence of a large excess of metal ion. At 25 °C. and ionic strength μ = 0.5 M, the stability constant of Ni(ApA) is evaluated to be K = 2.6 (±0.6) M^?1. The low stability is taken as evidence that the predominant complex species is one in which the ApA acts as a monodentate ligand, mainly through the adenine group. The rate constants for complex formation and dissociation, k_f = 1430 M^?1 s^?1 and k_b = 665 s^?1 (25°C. μ = 0.5M). determined by the temperature-jump relaxation technique, are consistent with this interpretation. The binding strength of Ni²⁺ to poly(adenylic acid) [poly(A)] has been studied at pH 7.0 using murexide as an indicator of the concentration of free Ni²⁺. Within the concentration range [Ni²⁺ = 1 × 10^?5 × 10^?3 M the data can be represented in the form of a linear Scatchard plot. i.e., the process can be described as the binding of Ni²⁺ to one class of independent binding sites. The number of binding sites per monomer is 0.26, and the stability constant K = 8.2×10³ M^?1 (25°C μ = 0.1 M). In kinetic studies of the reaction of Ni²⁺ with poly(A), two relaxation effects due to complex formation were detected, one with a concentration-independent time constant of about 0.4 ms, the other with a concentration-dependent time constant in the millisecond range. The concentration dependence of the longer relaxation time can be accounted for by a three-step mechanism which consists of a fast second-order association reaction followed by two first-order steps. There is evidence, however, that the overall process is more complicated than expressed by the three-step mechanism.     

Enzymatic Saccharification of Lignocelluloses Should be Conducted at Elevated pH 5.2–6.2

This study revealed that cellulose enzymatic saccharification response curves of lignocellulosic substrates were very different from those of pure cellulosic substrates in terms of optimal pH and pH operating window. The maximal enzymatic cellulose saccharification of lignocellulosic substrates occurs at substrate suspension pH 5.2–6.2, not between pH 4.8 and 5.0 as exclusively used in literature using T. reesi cellulase. Two commercial cellulase enzyme cocktails, Celluclast 1.5L and CTec2 both from Novozymes, were evaluated over a wide range of pH. The optimal ranges of measured suspension pH of 5.2–5.7 for Celluclast 1.5L and 5.5–6.2 for CTec2 were obtained using six lignocellulosic substrates produced by dilute acid, alkaline, and two sulfite pretreatments to overcome recalcitrance of lignocelluloses (SPORL) pretreatments using both a softwood and a hardwood. Furthermore, cellulose saccharification efficiency of a SPORL-pretreated lodgepole pine substrate showed a very steep increase between pH 4.7 and 5.2. Saccharification efficiency can be increased by 80 % at cellulase loading of 11.3 FPU/g glucan, i.e., from approximately 43 to 78 % simply by increasing the substrate suspension pH from 4.7 to 5.2 (buffer solution pH from 4.8 to 5.5) using Celluclast 1.5L, or by 70 % from approximately 51 to 87 % when substrate suspension pH is increased from 4.9 to 6.2 (buffer solution pH from 5.0 to 6.5) using CTec2. The enzymatic cellulose saccharification response to pH is correlated to the degree of substrate lignin sulfonation. The difference in pH-induced lignin surface charge, and therefore surface hydrophilicity and lignin–cellulase electrostatic interactions, among different substrates with different lignin content and structure is responsible for the reported different enhancements in lignocellulose saccharification at elevated pH.     

Kinetics of reduction of ferrioxamine B by chromium(II), vanadium(II), and dithionite

Kinetic studies of the reduction of ferrioxamine B (Fe(Hdesf)⁺) by Cr(H₂O)₆²⁺, V(H₂O)₆²⁺, and dithionite have been performed. For Cr(H₂O)₆²⁺ and V(H₂O)₆²⁺, the rate is ?d[Fe(Hdesf)⁺]/dt = k[Fe(Hdesf)⁺][M²⁺]. For Cr(H₂O)₆²⁺, k = 1.19 × 10⁴ M^?1 sec^?1 at 25°C and μ = 0.4 M, and k is independent of pH from 2.6 to 3.5. For V(H₂O)₆²⁺, k = 6.30 × 10² M^?1 sec^?1 at 25°C, μ = 1.0 M, and pH = 2.2. The rate is nearly independent of pH from 2.2 to 4.0. For Cr(H₂O)₆²⁺ and V(H₂O)₆²⁺, the activation parameters are ΔH^≠ = 8.2 kcal mol^?1, ΔS^≠ ?12 eu and ΔH^≠ = 1.7 kcal mol^?1, ΔS^≠ = ?40 eu (at pH 2.2) respectively. Reduction by Cr(H₂O)₆²⁺ is inner-sphere, while reduction by V(H₂O)₆²⁺ is outer-sphere. Reduction by dithionite follows the rate law ?d[Fe(Hdesf)⁺]/dt =kK^{$\text{1}\text{2}$}[Fe(Hdesf)⁺][S₂O₄^2?]^{$\text{1}\text{2}$} where K is the equilibrium constant for dissociation of S₂O₄^2? into SO₂^? radicals. The value of k at 25°C and μ = 0.5 is 2.7 × 10³ M^?1 sec^?1 at pH 5.8, 3.5 × 10³ M^?1 sec^?1 at pH 6.8, and 4.6 × 10³ M^?1 sec^?1 at pH 7.8, and ΔH^≠ = 6.8 kcal mol^?1 and ΔS^≠ = ?19 eu at pH 7.8.     

Anacardic acid-mediated changes in membrane potential and pH gradient across liposomal membranes

We have previously shown that anacardic acid has an uncoupling effect on oxidative phosphorylation in rat liver mitochondria using succinate as a substrate (Life Sci. 66 (2000) 229-234). In the present study, for clarification of the physicochemical characteristics of anacardic acid, we used a cyanine dye (DiS-C3(5)) and 9-aminoacridine (9-AA) to determine changes of membrane potential (ΔΨ) and pH difference (ΔpH), respectively, in a liposome suspension in response to the addition of anacardic acid to the suspension. The anacardic acid quenched DiS-C3(5) fluorescence at concentrations higher than 300 nM, with the degree of quenching being dependent on the log concentration of the acid. Furthermore, the K⁺ diffusion potential generated by the addition of valinomycin to the suspension decreased for each increase in anacardic acid concentration used over 300 nM, but the sum of the anacardic acid- and valinomycin-mediated quenching was additively increasing. This indicates that the anacardic acid-mediated quenching was not due simply to increments in the K⁺ permeability of the membrane. Addition of anacardic acid in the micromolar range to the liposomes with ΔΨ formed by valinomycin-K⁺ did not significantly alter 9-AA fluorescence, but unexpectedly dissipated ΔΨ. The ΔΨ preformed by valinomycin-K⁺ decreased gradually following the addition of increasing concentrations of anacardic acid. The ΔΨ dissipation rate was dependent on the pre-existing magnitude of ΔΨ, and was correlated with the logarithmic concentration of anacardic acid. Furthermore, the initial rate of ΔpH dissipation increased with logarithmic increases in anacardic acid concentration. These results provide the evidence for a unique function of anacardic acid, dissimilar to carbonylcyanide p-trifluoromethoxyphenylhydrazone or valinomycin, in that anacardic acid behaves as both an electrogenic (negative) charge carrier driven by ΔΨ, and a ‘proton carrier’ that dissipates the transmembrane proton gradient formed.     

Effect of Fermentation Conditions on Growth of Streptococcus cremoris AM2 and Leuconostoc lactis CNRZ 1091 in Pure and Mixed Cultures

Two strains of mesophilic lactic acid bacteria, Streptococcus cremoris AM2 and Leuconostoc lactis CNRZ 1091, were grown in pure and mixed cultures in the presence or absence of citrate (15 mM) and at controlled (pH 6.5) or uncontrolled pH. Microbial cell densities at the end of growth, maximum growth rates, the pH decrease of the medium resulting from growth, and the corresponding acidification rates were determined to establish comparisons. The control of pH in pure cultures had no effect on L. lactis CNRZ 1091 populations. The final populations of S. cremoris AM2, however, were at least five times higher than when the pH was not controlled (4 × 10⁸ vs. 2 × 10⁹ CFU · ml⁻¹). The pH had no effect on the growth rate of either strain. That of S. cremoris AM2 (0.8 h⁻¹) was about twice that of L. lactis CNRZ 1091. When the pH fell below 5, the growth of both strains decreased or stopped altogether. Citrate had no effect on S. cremoris AM2, while final populations of L. lactis CNRZ 1091 were two to three times higher (3 × 10⁸ CFU · ml⁻¹); it had no effect on the maximum growth rates of the two strains. Citrate attenuated the pH decrease of the medium and reduced the maximum acidification rate of the culture by 50%, due to the growth of S. cremoris AM2. Acidification due to L. lactis CNRZ 1091, however, was very slight. Regardless of the conditions of pH and citrate, the total bacterial population in mixed culture was lower (by 39%) than that of the sum of each pure culture. Mixed culture improved the maximum growth rate of L. lactis CNRZ 1091 (0.6 h⁻¹) by 50%, while that of S. cremoris AM2 was unaffected. The acidification rate of the growth medium in mixed culture, affected by the presence of citrate, resulted from the development and activity of S. cremoris AM2.     

Standard free energy maps for the hydrolysis of ATP as a function of pH and metal ion concentration: comparison of metal ions

The observed equilibrium constant K_obs for the hydrolysis of ATP to ADP and inorganic phosphate has been calculated as a function of pH and metal ion concentration pM (- log [M]) at 25 °C and μ = 0.2 with the use of literature values of the acid dissociation and complex dissociation constants for the phosphates.The resulting standard free energy changes ΔG °′ are presented by means of contour diagrams for the range pH 4–10 and pM 1–7. These maps summarize the results of some 1900 calculations per diagram, and clearly simulate a differential effect of the metal ions of interest, including Mg²⁺, Ca²⁺, Sr²⁺, Mn²⁺, Li⁺, Na⁺ and K⁺, on the equilibrium hydrolysis of ATP.     

Efflux and Influx of Erythrocyte Water

Rabbit erythrocytes were washed in buffered NaCl solutions isotonic with rabbit serum (Δ^t -0.558°C.) and suspended in buffered NaCl solutions of tonicity equidistant from intracellular tonicity (Δ^t = -0.558°C. ± 0.112°C.) of varying pH and incubated at varying temperatures. After incubation, the freezing point depression (Δ^t) was measured on the supernatant. Change in the Δ^t measured change in the water content of the extracellular solutions—water being withdrawn by erythrocytes (W_I) from the hypotonic solutions and added (W_E) to the hypertonic solutions. W_E was always less than W_I and was inversely proportional to the pH in the range 6.5–8.0. W_E was significantly increased by lowering the temperature of the cell suspension to 4°C. W_I was increased by raising or lowering the pH or raising the temperature of the cell suspension. W_E x W_I ≠ k. W_E and W_I were affected differently by changes in pH and temperature. It was concluded that W_E and W_E were probably under different physicochemical control.     

Predictive modeling of β-carotene accumulation by Dunaliella salina as a function of pH,NaCI, and irradiance

Predictive modeling of β-carotene accumulation by Dunaliella salina as a function of NaCI, pH, and irradiance was studied. Modified Logistic, Gompertz, Schnute, Richards, and Stannard models were fitted to describe β-carotene accumulation by the alga under various environmental conditions. Lag time (λ, days), maximum accumulation (A, pg/cell), and the maximum production rate (μ, 1/day) for β-carotene accumulation were calculated by modified Logistic and Gompertz models. Values of λ, A, and μ for β-carotene accumulation varied between 0.26 and 20.14 days, 57.48 to 198.76 pg β-carotene/cell, and 1.80 to 3.68 1/day, respectively. Results revealed that Logistic and Gompertz models could be used to describe the accumulation of β-carotene by D. salina as a function of salt concentrations, pH, and irradiance. The highest asymptotic value was predicted from Logistic and Gompertz models at pH 9.0, 48 kerg/(cm² s) light intensity, and 20% NaCl concentration.     

Theileria parva: isolation of macroschizonts from in vitro propagated lymphoblastoid cells of cattle

A method for purifying macroschizonts of Theileria parva from bovine lymphoblastoid cells, propagated in vitro, was developed. This method involved three steps. First, the macroschizonts were liberated by disrupting host cells suspended in growth medium at 4 × 10⁶ cells/ml at 300–400 psi, using the Stansted cell disrupter. This yielded 80–90% disrupted cells while causing minimum damage to the macroschizonts. Second, the host cell nuclei were separated by (a) centrifuging the lysate at 300g for 60 min, (b) resuspending the pellet in 0.02 times the volume of initial host cell suspension in Leibovitz's L15 growth medium, and (c) lysing the host cell nuclei by adding nucleus-lysing buffer (NLB, containing 0.14 M Tris, 0.1 M HCl, 0.12 M glucose, and 0.5 M NaCl adjusted with NaOH to pH 7) to 0.2 times the volume of initial host cell suspension. The resulting chromatin precipitate was removed by adding DE-52 cellulose equilibrated with NLB and allowing the precipitate to sediment. Lastly, the final suspension obtained in the second step was applied on a DE-52 cellulose column which was equilibrated with the elution buffer (NLB with 10% fetal, or newborn, bovine serum, pH 7). Macroschizonts free of intact host cells and naked host cell nuclei were collected in the eluate. The protein yield was 2.7 mg per 10⁹ starting undisrupted host cells, which was 1.7% of the total starting protein.     

Cytoplasmic pH Regulation in Acer pseudoplatanus Cells: I. A P NMR Description of Acid-Load Effects

Modifications of cytoplasmic pH in Acer pseudoplatanus L. cells cultivated in suspension have been induced by acid-loads and studied by using ³¹P nuclear magnetic resonance spectroscopy. The initial drop of cytoplasmic pH, observed in the first minutes of exposure to weak lipophilic acids, was followed by a slow recovery to reach a plateau phase with a pH value lower than the initial one. Conversely, removal of the acid led to a sharp increase of cytoplasmic pH with in most cases an overshoot toward more alkaline values than the initial one and a subsequent decrease to more acidic values. This shows that A. pseudoplatanus cells powerfully regulate their cytoplasmic pH both on the acid side of their normal pH, during the acid-load, and on the alkaline side, after removal of acid. Similar results were obtained with different types of acid-loads, i.e. treatments with propionic or benzoic acid or bubbling with CO₂-enriched air. This indicates that the occurrence of pH regulation does not depend upon the method used to acid-load the cells. The time courses of cytoplasmic pH observed for A. pseudoplatanus and also Catharanthus roseus cells are similar to those recorded for animal cells but different from those described for other plant materials for which no recovery phase was observed. This can be explained by different balances between the initial rate of proton influx brought in by the acids, and the capacity of proton consumption by the regulatory mechanisms. The existence of the recovery phase offers a unique possibility to study the regulation of the cytoplasmic pH of plant cells, as it has been done in animal systems.     

The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M ^{0.17±0.08 (95% CI)}, jump take-off angle (A; degrees) scales as A = 52.5M ^0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M ^1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q₁₀ of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L _f+t; mm) of the femur and tibia of the hind leg, L _f+t = 34.9M ^0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur''s cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur''s cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.     

Cation Transport in Escherichia coli : III. Potassium fluxes in the steady-state

The present study is concerned with the measurement of the unidirectional K flux in E. coli. Methods are described by means of which a fairly dense suspension of cells may be maintained in a well defined steady-state with respect to the intracellular K concentration and the pH of the medium. The kinetics of K⁴² exchange under these conditions are consistent with the presence of a single intracellular K compartment with a unidirectional K flux of 1 pmol/(cm² sec.). This rate is independent of the extracellular K concentration over the range studied. The simultaneous rate of H secretion averages 16 pmols/(cm² sec.) indicating that in the steady-state the efflux of metabolically produced H is not linked mole for mole to K movement.