THE GEOTROPIC RESPONSE IN ASTERINA

Upon a surface inclined at angle α Asterina gibbosa orients upward during negatively geotropic creeping until the average angle (θ) of the path is such that Δ sin θ/Δ sin α = const. This is true also in positively geotropic movement. The direction of orientation may be temporarily reversed by mechanical disturbance. The variation of θ is greater at low slopes. Tests with directed impressed pulls, due to an attached cork float, show that the pull upon the tube feet is of primary consequence for the determination of θ. When the component of gravitational pull in the direction of movement reaches a fraction of the total pull which is proportional to the gravitational vector parallel to the surface, the laterally acting component is ineffective. On this basis, it follows that Δ sin θ/Δ sin α = const.     

GEOTROPIC ORIENTATION IN ARTHROPODS : I. MALACOSOMA LARV?.

The geotropic orientation of caterpillars of Malacosoma americana during progression upon a surface inclined at angle α to the horizontal is such that the path makes an average angle θ upward on the plane, of a magnitude proportional to log sin α. More precisely, the product (sin α) (sin θ) is constant. This is traced to the fluctuation of the pull of the head region upon the lateral musculature of the upper side during the side to side swinging implicated in progression.     

ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. II

1. Equations describing the geotropic orientation of young rats as a function of the inclination of the surface on which creeping take place, under standardized conditions, are found to be of similar form but with different values of the contained constants, when several different, genetically stabilized lines or races are compared. The values of these constants are characteristic for the several races. 2. The biological "reality" of the differences between young rats of two races, as given mathematical form in terms of these parameters and coefficients, can be submitted to radical test by investigating their behavior in inheritance. A simple result favorable to the inquiry would be decisive; a complex, non-clear result would not however be definitely unfavorable to the view that "real" differences in behavior are in question. The actual result is of a kind demonstrating (a) the efficiency of the original formulations, and (b), at the same time, the definite inheritance of certain quantitative aspects of geotropic behavior. 3. On the assumption that orientation on a sloping surface is achieved when, within a threshold difference, the tension-excitations on the two sides of the body (legs) are the same, the angle of oriented progression (θ) can be taken as a direct measure of the total excitation. This is consistent with the equation, accurately obeyed by our initial races, Δ cos θ/Δ sin α = - const., where α is the slope of the surface. 4. The total excitation of tension-receptors must be regarded as involving, over a gross interval of time, (1) the total array of receptors with thresholds below a certain value, a function of the stretching force, and (2) the frequency of change of tension. The latter, largely determined (it is assumed) by the frequency of stepping, should be proportional to the speed of progression. This speed is directly proportional to log sin α. Hence Δθ/Δ log sin α. plotted against sin α, should give a picture of the distribution of effective thresholds among the available tension-receptors in terms of the exciting component of gravity. For the races investigated this distribution can be resolved in each case into three groups. 5. A "variability number" is employed which permits the demonstration that the variability of θ as measured is (1) definitely controlled by α, and is (2) a characteristic number for each of the pure races used. 6. By attaching a weight to rats of one race it is found that Δθ/Δα is modified in a manner concordant with the assumption that the three "groups of sense organs" are in fact discrete. 7. In race K these three groups (I, II, III) are large, in race A, small (i, ii, iii). F₁ rats of the cross between these two races show i, ii, III. 8. F₁ individuals back-crossed to A give in the progeny two sorts of individuals, in equal numbers: i, ii, III and i, ii, iii. 9. F₁ individuals back-crossed to K are expected to give in the progeny four types of individuals, I, II; i, II; I, ii; i, ii. In the numbers available these classes are reasonably clear, and occur with equal frequency. 10. It is pointed out that these considerations imply a mode of definition of a gene somewhat different from that commonly employed by tacit assumption; namely, a definition of the effect in inheritance as a function of some controlling, independent variable.     

Accelerated Recovery of Mitochondrial Membrane Potential by GSK-3β Inactivation Affords Cardiomyocytes Protection from Oxidant-Induced Necrosis

Loss of mitochondrial membrane potential (ΔΨ_m) is known to be closely linked to cell death by various insults. However, whether acceleration of the ΔΨ_m recovery process prevents cell necrosis remains unclear. Here we examined the hypothesis that facilitated recovery of ΔΨ_m contributes to cytoprotection afforded by activation of the mitochondrial ATP-sensitive K⁺ (mK_ATP) channel or inactivation of glycogen synthase kinase-3β (GSK-3β). ΔΨ_m of H9c2 cells was determined by tetramethylrhodamine ethyl ester (TMRE) before or after 1-h exposure to antimycin A (AA), an inducer of reactive oxygen species (ROS) production at complex III. Opening of the mitochondrial permeability transition pore (mPTP) was determined by mitochondrial loading of calcein. AA reduced ΔΨ_m to 15±1% of the baseline and induced calcein leak from mitochondria. ΔΨ_m was recovered to 51±3% of the baseline and calcein-loadable mitochondria was 6±1% of the control at 1 h after washout of AA. mK_ATP channel openers improved the ΔΨ_m recovery and mitochondrial calcein to 73±2% and 30±7%, respectively, without change in ΔΨ_m during AA treatment. Activation of the mK_ATP channel induced inhibitory phosphorylation of GSK-3β and suppressed ROS production, LDH release and apoptosis after AA washout. Knockdown of GSK-3β and pharmacological inhibition of GSK-3β mimicked the effects of mK_ATP channel activation. ROS scavengers administered at the time of AA removal also improved recovery of ΔΨ_m. These results indicate that inactivation of GSK-3β directly or indirectly by mK_ATP channel activation facilitates recovery of ΔΨ_m by suppressing ROS production and mPTP opening, leading to cytoprotection from oxidant stress-induced cell death.     

Influence of Transepithelial Potential Difference on the Sodium Uptake at the Outer Surface of the Isolated Frog Skin

The unidirectional uptake of sodium across the outer surface of the isolated frog skin (J₁₂^Na) was measured in the presence of transepithelial potential difference (Δ_ψ) ranging from +100 to -100 mV. With a sodium concentration of 115 mM in the bathing solutions J₁₂^Na increases significantly when the spontaneous Δ_ψ is reduced to zero by short-circuiting the skin. With an Na concentration of 6 mM a progressive increase J₁₂^Na can be observed when Δ_ψ is decreased in several steps from +100 to -100 mV (serosal side positive and negative, respectively). The observed change J₁₂^Na amounts to a fraction only of that predicted from the shift in Δ_ψ. The results suggest that under open circuit conditions the potential step across the outside surface is at most one half of Δ_ψ and that the resistance across the outside and inside barrier of the skin is ohmic. This is in agreement with measurements of intracellular potentials in the frog skin and with resistance measurements carried out in the toad skin. The data strongly support the view that the saturating component of J_ψ proceeds via a charged carrier system. Exposure to negative values of Δ_ψ of 50 mV or more for times of 24 min or more result in a marked reduction of J₁₂^Na which shows only partial or no reversibility.     

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.     

Identification of Novel α1,3-Galactosyltransferase and Elimination of α-Galactose-containing Glycans by Disruption of Multiple α-Galactosyltransferase Genes in Schizosaccharomyces pombe

The oligosaccharides from fission yeast Schizosaccharomyces pombe contain large amounts of d-galactose (Gal) in addition to d-mannose (Man), in contrast to the budding yeast Saccharomyces cerevisiae. Detailed structural analysis has revealed that the Gal residues are attached to the N- and O-linked oligosaccharides via α1,2- or α1,3-linkages. Previously we constructed and characterized a septuple α-galactosyltransferase disruptant (7GalTΔ) anticipating a complete lack of α-Gal residues. However, the 7GalTΔ strain still contained oligosaccharides consisting of α1,3-linked Gal residues, indicating the presence of at least one more additional unidentified α1,3-galactosyltransferase. In this study we searched for unidentified putative glycosyltransferases in the S. pombe genome sequence and identified three novel genes, named otg1⁺–otg3⁺ (α one, three-galactosyltransferase), that belong to glycosyltransferase gene family 8 in the Carbohydrate Active EnZymes (CAZY) database. Gal-recognizing lectin blotting and HPLC analyses of pyridylaminated oligosaccharides after deletion of these three additional genes from 7GalTΔ strain demonstrated that the resultant disruptant missing 10 α-galactosyltransferase genes, 10GalTΔ, exhibited a complete loss of galactosylation. In an in vitro galactosylation assay, the otg2⁺ gene product had Gal transfer activity toward a pyridylaminated Man₉GlcNAc₂ oligosaccharide and pyridylaminated Manα1,2-Manα1,2-Man oligosaccharide. In addition, the otg3⁺ gene product exhibited Gal transfer activity toward the pyridylaminated Man₉GlcNAc₂ oligosaccharide. Generation of an α1,3-linkage was confirmed by HPLC analysis, α-galactosidase digestion analysis, ¹H NMR spectroscopy, and LC-MS/MS analysis. These results indicate that Otg2p and Otg3p are involved in α1,3-galactosylation of S. pombe oligosaccharides.     

Effect of Steric and Nuclear Changes in Steroids and Triterpenoids on Sexual Reproduction in Phytophthora cactorum

The comparative biological activity of 21 naturally occurring or synthetically derived steroids, 7 tetracyclic and pentacylic triterpenoids, and antheridiol incubated with cultures of Phytophthora cactorum has been examined. There was greater dependence on precise steric features of the sterol side chain than on the extent of nuclear unsaturation in inducing oospore formation. There was no significant effect on oospore formation by changing nuclear unsaturation in ring B from Δ⁵ to Δ⁷ or to Δ^5,7. Converting the unsaturated sterol to its corresponding stanol resulted in a significant reduction in the number of oospores produced. The effectiveness of sterols bearing different side chains in inducing oospores was found to be in the following relative order: 24α-ethyl = trans-Δ²²-24α-ethyl > trans-Δ²²-24β-ethyl = 24α-E-ethylidene = 24α-methyl > 24β-methyl = trans-Δ²²-24β-methyl = 26-methyl = saturated C₇ side chain and C-20 R (17-αH, 20-αH, right-handed conformer) = cis-Δ²²-C₇ side chain and C-20 R > saturated C₇ side chain and C-20 S (17-αH, 20-βH, right-handed conformer) > no sterol = 29-hydroxyporiferasterol = 20α-hydroxycholesterol = 24ξ-hydroxy-24-vinylcholesterol. Of the sterols examined the most significant stereochemical criterion for the induction of oospore formation was absence of bulk on the front face of C-20. This follows from the observation that 20-isocholesterol and 20α-hydroxycholesterol, in which a methyl and hydroxy group, respectively, project to the front in the right handed conformation, were inactive in stimulating production of oospores. None of the triterpenoids studied induced oospore formation to any significant degree. Oospore formation was not induced by antheridiol nor 29-hydroxyporiferasterol in combination or added separately to growing cultures of P. cactorum in the concentration range 0.01 - 10.0 milligrams per liter.     

Mitochondrial Networks in Cardiac Myocytes Reveal Dynamic Coupling Behavior

Oscillatory behavior of mitochondrial inner membrane potential (ΔΨ_m) is commonly observed in cells subjected to oxidative or metabolic stress. In cardiac myocytes, the activation of inner membrane pores by reactive oxygen species (ROS) is a major factor mediating intermitochondrial coupling, and ROS-induced ROS release has been shown to underlie propagated waves of ΔΨ_m depolarization as well as synchronized limit cycle oscillations of ΔΨ_m in the network. The functional impact of ΔΨ_m instability on cardiac electrophysiology, Ca²⁺ handling, and even cell survival, is strongly affected by the extent of such intermitochondrial coupling. Here, we employ a recently developed wavelet-based analytical approach to examine how different substrates affect mitochondrial coupling in cardiac cells, and we also determine the oscillatory coupling properties of mitochondria in ventricular cells in intact perfused hearts. The results show that the frequency of ΔΨ_m oscillations varies inversely with the size of the oscillating mitochondrial cluster, and depends on the strength of local intermitochondrial coupling. Time-varying coupling constants could be quantitatively determined by applying a stochastic phase model based on extension of the well-known Kuramoto model for networks of coupled oscillators. Cluster size-frequency relationships varied with different substrates, as did mitochondrial coupling constants, which were significantly larger for glucose (7.78 × 10⁻² ± 0.98 × 10⁻² s⁻¹) and pyruvate (7.49 × 10⁻² ± 1.65 × 10⁻² s⁻¹) than lactate (4.83 × 10⁻² ± 1.25 × 10⁻² s⁻¹) or β-hydroxybutyrate (4.11 × 10⁻² ± 0.62 × 10⁻² s⁻¹). The findings indicate that mitochondrial spatiotemporal coupling and oscillatory behavior is influenced by substrate selection, perhaps through differing effects on ROS/redox balance. In particular, glucose-perfusion generates strong intermitochondrial coupling and temporal oscillatory stability. Pathological changes in specific catabolic pathways, which are known to occur during the progression of cardiovascular disease, could therefore contribute to altered sensitivity of the mitochondrial network to oxidative stress and emergent ΔΨ_m instability, ultimately scaling to produce organ level dysfunction.     

Immobilised Histidine Tagged β 2-Adrenoceptor Oriented by a Diazonium Salt Reaction and Its Application in Exploring Drug-Protein Interaction Using Ephedrine and Pseudoephedrine as Probes

A new oriented method using a diazonium salt reaction was developed for linking β ₂-adrenoceptor (β ₂-AR) on the surface of macroporous silica gel. Stationary phase containing the immobilised receptor was used to investigate the interaction between β ₂-AR and ephedrine plus pseudoephedrine by zonal elution. The isotherms of the two drugs best fit the Langmuir model. Only one type of binding site was found for ephedrine and pseudoephedrine targeting β ₂-AR. At 37 °C, the association constants during the binding were (5.94±0.05)×10³/M for ephedrine and (3.80±0.02) ×10³/M for pseudoephedrine, with the binding sites of (8.92±0.06) ×10⁻⁴ M. Thermodynamic studies showed that the binding of the two compounds to β ₂-AR was a spontaneous reaction with exothermal processes. The ΔG^θ, ΔH^θ and ΔS^θ for the interaction between ephedrine and β ₂-AR were −(22.33±0.04) kJ/mol, −(6.51±0.69) kJ/mol and 50.94±0.31 J/mol·K, respectively. For the binding of pseudoephedrine to the receptor, these values were −(21.17±0.02) kJ/mol, −(7.48±0.56) kJ/mol and 44.13±0.01 J/mol·K. Electrostatic interaction proved to be the driving force during the binding of the two drugs to β ₂-AR. The proposed immobilised method will have great potential for attaching protein to solid substrates and realizing the interactions between proteins and drugs.     

Function of Interfacial Prolines at the Transmitter-binding Sites of the Neuromuscular Acetylcholine Receptor

The neuromuscular acetylcholine (ACh) receptor has two conserved prolines in loop D of the complementary subunit at each of its two transmitter-binding sites (α-ϵ and α-δ). We used single-channel electrophysiology to estimate the energy changes caused by mutations of these prolines with regard to unliganded gating (ΔG₀) and the affinity change for ACh that increases the open channel probability (ΔG_B). The effects of mutations of ProD2 (ϵPro-121/δPro-123) were greater than those of its neighbor (ϵPro-120/δPro-122) and were greater at α-ϵ versus α-δ. The main consequence of the congenital myasthenic syndrome mutation ϵProD2-L was to impair the establishment of a high affinity for ACh and thus make ΔG_B less favorable. At both binding sites, most ProD2 mutations decreased constitutive activity (increased ΔG₀). LRYHQG and RL substitutions reduced substantially the net binding energy (made ΔG_B^ACh less favorable) by ≥2 kcal/mol at α-ϵ and α-δ, respectively. Mutant cycle analyses were used to estimate energy coupling between the two ProD2 residues and between each ProD2 and glycine residues (αGly-147 and αGly-153) on the primary (α subunit) side of each binding pocket. The distant binding site prolines interact weakly. ProD2 interacts strongly with αGly-147 but only at α-ϵ and only when ACh is present. The results suggest that in the low to-high affinity change there is a concerted inter-subunit strain in the backbones at ϵProD2 and αGly-147. It is possible to engineer receptors having a single functional binding site by using a α-ϵ or α-δ ProD2-R knock-out mutation. In adult-type ACh receptors, the energy from the affinity change for ACh is approximately the same at the two binding sites (approximately −5 kcal/mol).     

Controls of Evapotranspiration and CO2 Fluxes from Scots Pine by Surface Conductance and Abiotic Factors

Evapotranspiration (E) and CO₂ flux (F_c) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, F_c, surface conductance (g_c), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, F_c, g_c, and Ω were 1.78 mmol m⁻² s⁻¹, −11.18 µmol m⁻² s⁻¹, 6.27 mm s⁻¹, and 0.31, respectively, with seasonal averages of 0.71 mmol m⁻² s⁻¹, −4.61 µmol m⁻² s⁻¹, 3.3 mm s⁻¹, and 0.16. E and F_c were controlled by combined biological and environmental variables. There was curvilinear dependence of E on g_c and F_c on g_c. Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to F_c, while vapour pressure deficit was the most important environmental factor affecting g_c. Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO₂ (mmol H₂O)⁻¹ and a seasonal average of 7.06 μmol CO₂ (μmol H₂O)⁻¹. Low Ω and its close positive relationship with g_c indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.     

Apolipoprotein A-I Deficiency Increases Cerebral Amyloid Angiopathy and Cognitive Deficits in APP/PS1ΔE9 Mice

A hallmark of Alzheimer disease (AD) is the deposition of amyloid β (Aβ) in brain parenchyma and cerebral blood vessels, accompanied by cognitive decline. Previously, we showed that human apolipoprotein A-I (apoA-I) decreases Aβ₄₀ aggregation and toxicity. Here we demonstrate that apoA-I in lipidated or non-lipidated form prevents the formation of high molecular weight aggregates of Aβ₄₂ and decreases Aβ₄₂ toxicity in primary brain cells. To determine the effects of apoA-I on AD phenotype in vivo, we crossed APP/PS1ΔE9 to apoA-I^KO mice. Using a Morris water maze, we demonstrate that the deletion of mouse Apoa-I exacerbates memory deficits in APP/PS1ΔE9 mice. Further characterization of APP/PS1ΔE9/apoA-I^KO mice showed that apoA-I deficiency did not affect amyloid precursor protein processing, soluble Aβ oligomer levels, Aβ plaque load, or levels of insoluble Aβ in brain parenchyma. To examine the effect of Apoa-I deletion on cerebral amyloid angiopathy, we measured insoluble Aβ isolated from cerebral blood vessels. Our data show that in APP/PS1ΔE9/apoA-I^KO mice, insoluble Aβ₄₀ is increased more than 10-fold, and Aβ₄₂ is increased 1.5-fold. The increased levels of deposited amyloid in the vessels of cortices and hippocampi of APP/PS1ΔE9/apoA-I^KO mice, measured by X-34 staining, confirmed the results. Finally, we demonstrate that lipidated and non-lipidated apoA-I significantly decreased Aβ toxicity against brain vascular smooth muscle cells. We conclude that lack of apoA-I aggravates the memory deficits in APP/PS1ΔE9 mice in parallel to significantly increased cerebral amyloid angiopathy.     

Mitochondrial Free Ca2+ Levels and Their Effects on Energy Metabolism in Drosophila Motor Nerve Terminals

Mitochondrial Ca²⁺ uptake exerts dual effects on mitochondria. Ca²⁺ accumulation in the mitochondrial matrix dissipates membrane potential (_ΔΨ_m), but Ca²⁺ binding of the intramitochondrial enzymes accelerates oxidative phosphorylation, leading to mitochondrial hyperpolarization. The levels of matrix free Ca²⁺ ([Ca²⁺]_m) that trigger these metabolic responses in mitochondria in nerve terminals have not been determined. Here, we estimated [Ca²⁺]_m in motor neuron terminals of Drosophila larvae using two methods: the relative responses of two chemical Ca²⁺ indicators with a 20-fold difference in Ca²⁺ affinity (rhod-FF and rhod-5N), and the response of a low-affinity, genetically encoded ratiometric Ca²⁺ indicator (D4cpv) calibrated against known Ca²⁺ levels. Matrix pH (pH_m) and _ΔΨ_m were monitored using ratiometric pericam and tetramethylrhodamine ethyl ester probe, respectively, to determine when mitochondrial energy metabolism was elevated. At rest, [Ca²⁺]_m was 0.22 ± 0.04 μM, but it rose to ∼26 μM (24.3 ± 3.4 μM with rhod-FF/rhod-5N and 27.0 ± 2.6 μM with D4cpv) when the axon fired close to its endogenous frequency for only 2 s. This elevation in [Ca²⁺]_m coincided with a rapid elevation in pH_m and was followed by an after-stimulus _ΔΨ_m hyperpolarization. However, pH_m decreased and no _ΔΨ_m hyperpolarization was observed in response to lower levels of [Ca²⁺]_m, up to 13.1 μM. These data indicate that surprisingly high levels of [Ca²⁺]_m are required to stimulate presynaptic mitochondrial energy metabolism.     

Evidence for unbenignant nature of glucose as a replacement for water in purple membranes

The net angle (θ_α) between the seven helical segments of the bacteriorhodopsin (bR) polypeptide and the normal to the membrane plane of the purple membrane (PM) is ~0° when determined by oriented far-ultraviolet (UV) circular dichroism (OCD) and midinfrared linear dichroism (IRLD). However, θ_α is ~11° when determined by high-resolution electron cryo-microscopy and electron diffraction (EMD). The spectral studies are made with fresh hydrated PM films at ambient temperature, whereas diffraction studies are made with aged glucose-embedded PM at -120 to -268°. The current study presents oriented far-UV OCD results of hydrated PM films embedded with glucose, which can best be interpreted as a change in the magnitude of θ_α (Δθ_α) from 0 to 23° as a consequence of glucose embedment. Possible alternative explanations contrary to this conclusion are discussed and ruled out. Therefore, it is suggested that a θ_α of ~11° as determined by the EMD method may not be an intrinsic structural characteristic of the native PM but an induced one. The differences in the Δθ_α value due to glucose embedment as determined by the two different approaches (23 vs. 11°) may be attributed to the drastic differences in the experimental conditions used, especially temperature. It is expected that at extremely low temperatures protein dynamics would be highly restricted and Δθ_α relatively curtailed. It is concluded that glucose may not be as benign to biological structures as has been assumed in the past.     

Na+/K+-ATPase α-subunit (nkaα) Isoforms and Their mRNA Expression Levels,Overall Nkaα Protein Abundance,and Kinetic Properties of Nka in the Skeletal Muscle and Three Electric Organs of the Electric Eel,Electrophorus electricus

This study aimed to obtain the coding cDNA sequences of Na⁺/K⁺-ATPase α (nkaα) isoforms from, and to quantify their mRNA expression in, the skeletal muscle (SM), the main electric organ (EO), the Hunter’s EO and the Sach’s EO of the electric eel, Electrophorus electricus. Four nkaα isoforms (nkaα1c1, nkaα1c2, nkaα2 and nkaα3) were obtained from the SM and the EOs of E. electricus. Based on mRNA expression levels, the major nkaα expressed in the SM and the three EOs of juvenile and adult E. electricus were nkaα1c1 and nkaα2, respectively. Molecular characterization of the deduced Nkaα1c1 and Nkaα2 sequences indicates that they probably have different affinities to Na⁺ and K⁺. Western blotting demonstrated that the protein abundance of Nkaα was barely detectable in the SM, but strongly detected in the main and Hunter’s EOs and weakly in the Sach’s EO of juvenile and adult E. electricus. These results corroborate the fact that the main EO and Hunter’s EO have high densities of Na⁺ channels and produce high voltage discharges while the Sach’s EO produces low voltage discharges. More importantly, there were significant differences in kinetic properties of Nka among the three EOs of juvenile E. electricus. The highest and lowest V _max of Nka were detected in the main EO and the Sach’s EO, respectively, with the Hunter’s EO having a V _max value intermediate between the two, indicating that the metabolic costs of EO discharge could be the highest in the main EO. Furthermore, the Nka from the main EO had the lowest K_m (or highest affinity) for Na⁺ and K⁺ among the three EOs, suggesting that the Nka of the main EO was more effective than those of the other two EOs in maintaining intracellular Na⁺ and K⁺ homeostasis and in clearing extracellular K⁺ after EO discharge.     

Predicting Thermodynamic Properties of PBXTHs with New Quantum Topological Indexes

Novel group quantitative structure-property relationship (QSPR) models on the thermodynamic properties of PBXTHs were presented, by the multiple linear regression (MLR) analysis method. Four thermodynamic properties were studied: the entropy (S^θ), the standard enthalpy of formation (Δ_fH^θ), the standard Gibbs energy of formation (Δ_fG^θ), and the relative standard Gibbs energy of formation (Δ_RG^θ). The results by the formula indicate that the calculated and predicted data in this study are in good agreement with those in literature and the deviation is within the experimental errors. To validate the estimation reliability for internal samples and the predictive ability for other samples, leave-one-out (LOO) cross validation (CV) and external validation were performed, and the results show that the models are satisfactory.     

Removal and Recovery of Toxic Silver Ion Using Deep-Sea Bacterial Generated Biogenic Manganese Oxides

Products containing silver ion (Ag⁺) are widely used, leading to a large amount of Ag⁺-containing waste. The deep-sea manganese-oxidizing bacterium Marinobacter sp. MnI7-9 efficiently oxidizes Mn²⁺ to generate biogenic Mn oxide (BMO). The potential of BMO for recovering metal ions by adsorption has been investigated for some ions but not for Ag⁺. The main aim of this study was to develop effective methods for adsorbing and recovering Ag using BMO produced by Marinobacter sp. MnI7-9. In addition, the adsorption mechanism was determined using X-ray photoelectron spectroscopy analysis, specific surface area analysis, adsorption kinetics and thermodynamics. The results showed that BMO had a higher adsorption capacity for Ag⁺ compared to the chemical synthesized MnO₂ (CMO). The isothermal absorption curves of BMO and CMO both fit the Langmuir model well and the maximum adsorption capacities at 28°C were 8.097 mmol/g and 0.787 mmol/g, for BMO and CMO, respectively. The change in enthalpy (ΔH^θ) for BMO was 59.69 kJ/mol indicating that it acts primarily by chemical adsorption. The change in free energy (ΔG^θ) for BMO was negative, which suggests that the adsorption occurs spontaneously. Ag⁺ adsorption by BMO was driven by entropy based on the positive ΔS^θ values. The Ag⁺ adsorption kinetics by BMO fit the pseudo-second order model and the apparent activation energy of E_a is 21.72 kJ/mol. X-ray photoelectron spectroscopy analysis showed that 15.29% Ag⁺ adsorbed by BMO was transferred to Ag(0) and meant that redox reaction had happened during the adsorption. Desorption using nitric acid and Na₂S completely recovered the Ag. The results show that BMO produced by strain MnI7-9 has potential for bioremediation and reutilization of Ag⁺-containing waste.