Studies on the interaction between polyion and counterions by sound velocity (II)

Sound velocities in polyacrylate solutions neutralized by tetraalkylammonium hydroxide were measured at various concentrations of added NACl. From the results, the degree of counterion binding to polyion and the extent of the changes in hydration volume due to ion binding were determined as a function of the degree of neutralization, alpha. The ion binding accompanying the volume changes appeared above about alpha = 0.6 and the ion binding process depended on the charge density of the polyion. The effect of the size of the tetraalkylammonium ion on ion binding was negligibly small.     

Polarographic studies of ion binding in solutions of pepsin. II. Binding of thallous ions

The results of the application of a modified polarographic method to the study of binding of thallous ions in solutions of pepsin are reported. Isoionic solutions of pepsin were converted by using a cation exchange resin to solutions of thallous pepsin. The extent of ion binding was obtained as in the case of cadmium pepsin by assuming that only free, i.e., unbound, ions contribute to the diffusion and migration currents, respectively. However, the relations used previously for computing the degree of ion binding have been refined on the basis of experience acquired in a parallel study of solutions of thallous acrylate and polyacrylate, respectively.     

Experimental data and modelling of apparent molar volumes, isentropic compressibilities and refractive indices in aqueous solutions of glycine + NaCl

Experiments have been performed at 298.15 K to measure the density, sound velocity and refractive index of glycine in aqueous solutions of NaCl over a wide range of both glycine and NaCl concentrations. The values of apparent molar volume and isentropic compressibility of glycine were calculated from the measured data. The results show a positive transfer volume of glycine from an NaCl solution to a more concentrated NaCl solution. This indicates that the size of a glycine molecule is larger in a solution with higher NaCl concentration. The negative values of apparent isentropic compressibility imply that the water molecules around the glycine molecules are less compressible than the water molecules in the bulk solution. These effects are attributed to the doubly charged behaviour of glycine and to the formation of physically bonded ion-pairs between the charged groups of glycine and sodium and chloride ions. The formation of ion-pairs, whose extents of binding reactions depend on the concentrations of both NaCl and glycine, alter the hydration number of glycine. This also explains the reason for the increase in the size of glycine with an increase in the NaCl concentration. A model based on the Pitzer formalism has been developed to correlate the activity coefficient, apparent molar volume and isentropic compressibility of glycine in aqueous solutions of NaCl. The results show that the model can accurately correlate the interactions in aqueous solutions of glycine and NaCl.     

Acoustic Property Reconstruction of a Neonate Yangtze Finless Porpoise's (Neophocaena asiaeorientalis) Head Based on CT Imaging

The reconstruction of the acoustic properties of a neonate finless porpoise’s head was performed using X-ray computed tomography (CT). The head of the deceased neonate porpoise was also segmented across the body axis and cut into slices. The averaged sound velocity and density were measured, and the Hounsfield units (HU) of the corresponding slices were obtained from computed tomography scanning. A regression analysis was employed to show the linear relationships between the Hounsfield unit and both sound velocity and density of samples. Furthermore, the CT imaging data were used to compare the HU value, sound velocity, density and acoustic characteristic impedance of the main tissues in the porpoise’s head. The results showed that the linear relationships between HU and both sound velocity and density were qualitatively consistent with previous studies on Indo-pacific humpback dolphins and Cuvier’s beaked whales. However, there was no significant increase of the sound velocity and acoustic impedance from the inner core to the outer layer in this neonate finless porpoise’s melon.     

The release of monovalent counterions by addition of divalent countemons to aqueous solutions of maleic acid copolymer

Divalent cation binding and the release of monovalent cations accompanying the cation binding were experimentally studied by ion-selective electrode methods in aqueous solutions of copolymer of maleic acid and ethyl vinyl ether. It was found that in the process of Ca2+ addition, all the Ca2+ added was bound to polyions and the initially condensed Na+ was released in proportion to the concentration of the added Ca2+ up to the critical concentration of added Ca2+ at which the condensation of Ca2+ ceases. Values of the structural charge density parameter xi(s), were determined from the end-points of condensation of Ca2+. The process of Na+ release by adding Ca2+ was analyzed on the basis of the counterion condensation theory by using these xi(s) values. In addition, the relationship between the activity coefficient gamma-- of Ca2+ and degree of neutralization alpha in salt-free solutions was obtained from the Manning theory. Agreement between the calculated and experimental values was excellent in both cases.     

Spread of discrete structural changes in synthetic polyanionic gel: a model of propagation of a nerve impulse

Thin fibers of cross-linked polyacrylate gel were prepared by inducing polymerization reaction inside long glass or Tygon tubings. By immersing these gel fibers in salt solutions containing both Ca(2+) and Na(+) at varying ratios, a discontinuous transition from the swollen state to the shrunken was demonstrated. A very sharp boundary was observed between the swollen and shrunken portions of the gel fiber. It was found possible to displace this sharp boundary continuously by application of a weak electric current. Based on the similarity in swelling behavior between nerve fibers and synthetic gel fibers, a non-myelinated nerve fiber carrying an impulse was treated as a cylindrical gel layer consisting of two distinct portions, a swollen (active) portion connected directly to the remaining shrunken (resting) portion. By applying the cable theory to this model of the nerve fiber, mathematical expressions describing the conduction velocity, the maximum rate of potential rise, etc. in terms of the electric parameters of the fiber were derived.     

Effects of phosphate and ADP on shortening velocity during maximal and submaximal calcium activation of the thin filament in skeletal muscle fibers.

The effects of added phosphate and MgADP on unloaded shortening velocity during maximal and submaximal Ca2+ activation of the thin filament were examined in skinned single skeletal fibers from rabbit psoas muscle. During maximal Ca2+ activation, added phosphate (10-30 mM) had no effect on unloaded shortening velocity as determined by the slack-test technique. In fibers activated at submaximal concentrations of Ca2+ in the absence of added phosphate, plots of slack length versus duration of unloaded shortening were biphasic, consisting of an initial high velocity phase of shortening and a subsequent low velocity phase of shortening. Interestingly, in the presence of added phosphate, biphasic slack-test plots were no longer apparent. This result was obtained in control fibers over a range of submaximal Ca2+ concentrations and in maximally Ca2+ activated fibers, which were first treated to partially extract troponin C. Thus, under conditions that favor the appearance of biphasic shortening (i.e., low [Ca2+], troponin C extraction), added phosphate eliminated the low velocity component. In contrast, in fibers activated in the presence of 5 mM added MgADP, biphasic slack-test plots were apparent even during maximal Ca2+ activation. The basis of biphasic shortening is not known but it may be due to the formation of axially compressed cross-bridges that become strained to bear a tension that opposes the relative sliding of the myofilaments. The present findings could be explained if added phosphate and MgADP bind to cross-bridges in a strain-dependent manner. In this case, the results suggest that phosphate inhibits the formation of cross-bridges that bear a compressive strain. Added MgADP, on the other hand, may be expected to detain cross-bridges in strong binding states, thus promoting an increase in the population of cross-bridges bearing a compressive strain. Alterations in the population of strained cross-bridges by added phosphate and MgADP would alter the internal load within the fiber and thus affect the speed of fiber shortening.     

Fluorescence polarization studies of the interactions between protamine and enzymes in aqueous solutions

Fluorescence polarization has been used to study the interaction of dansylated protamine with the enzymes: pepsin, α-chymotrypsin, alkaline phosphatase and invertase. These interactions have been compared with those between dansylated protamine and polyacrylate, or polyvinylsulphate. Each of the various complexes was found to be dissociated by the addition of sodium nitrate and a critical electrolyte concentration (CEC) was determined for each system, to allow assessment of the relative order of binding to the dansylated protamine. This order was: polyvinylsulphate >pepsin >polyacrylate >alkaline phosphatase >α-chymotrypsin. The strength of binding was also assessed by determination of a binding constant, K_a. The values of K_a showed the same relative order of binding as the CEC values. Invertase behaved similarly to the other enzymes, but it was not possible to obtain an unambiguous assessment of the comparative strength of binding. In each case, the stoichiometry of the complex was also determined.     

Controlling propulsive forces in gait initiation in transfemoral amputees

During prosthetic gait initiation, transfemoral (TF) amputees control the spatial and temporal parameters that modulate the propulsive forces, the positions of the center of pressure (CoP), and the center of mass (CoM). Whether their sound leg or the prosthetic leg is leading, the TF amputees reach the same end velocity. We wondered how the CoM velocity build up is influenced by the differences in propulsive components in the legs and how the trajectory of the CoP differs from the CoP trajectory in able bodied (AB) subjects. Seven TF subjects and eight AB subjects were tested on a force plate and on an 8 m long walkway. On the force plate, they initiated gait two times with their sound leg and two times with their prosthetic leg. Force measurement data were used to calculate the CoM velocity curves in horizontal and vertical directions. Gait initiated on the walkway was used to determine the leg preference. We hypothesized that because of the differences in propulsive components, the motions of the CoP and the CoM have to be different, as ankle muscles are used to help generate horizontal ground reaction force components. Also, due to the absence of an active ankle function in the prosthetic leg, the vertical CoM velocity during gait initiation may be different when leading with the prosthetic leg compared to when leading with the sound leg. The data showed that whether the TF subjects initiated a gait with their prosthetic leg or with their sound leg, their horizontal end velocity was equal. The subjects compensated the loss of propulsive force under the prosthesis with the sound leg, both when the prosthetic leg was leading and when the sound leg was leading. In the vertical CoM velocity, a tendency for differences between the two conditions was found. When initiating gait with the sound leg, the downward vertical CoM velocity at the end of the gait initiation was higher compared to when leading with the prosthetic leg. Our subjects used a gait initiation strategy that depended mainly on the active ankle function of the sound leg; therefore, they changed the relative durations of the gait initiation anticipatory postural adjustment phase and the step execution phase. Both legs were controlled in one single system of gait propulsion. The shape of the CoP trajectories, the applied forces, and the CoM velocity curves are described in this paper.     

白鱀豚额隆声衰减和声速的测量

本文用水浴法测试了白鱀豚额隆切片标本沿体轴方向的声压衰减系数和声速。实验表明额隆内有若干点声衰减为负值及零值、意味着声波沿这些点传输时、声压非但不减小反而增大了。再将这些点连接起来看、恰巧和从左、右鼻栓到头前部的水之间的声传输相一致、这两条途径看起来有点像小声道似的。     

Velocity and attenuation of sound in the isolated fetal lung as it is expanded with air.

We measured the velocity and attenuation of audible sound in the isolated lung of the near-term fetal sheep to test the hypothesis that the acoustic properties of the lung provide a measure of the volume of gas it contains. We introduced pseudorandom noise (bandwidth 70 Hz-7 kHz) to one side of the lung and recorded the noise transmitted to the surface immediately opposite, starting with the lung containing only fetal lung liquid and making measurements after stepwise inflation with air until a leak developed. The velocity of sound in the lung fell rapidly from 187 +/- 28.2 to 87 +/- 3.7 m/s as lung density fell from 0.93 +/- 0.01 to 0.75 +/- 0.01 g/ml (lung density = lung weight/gas volume plus lung tissue volume). For technical reasons, no estimate of velocity could be made before the first air injection. Thereafter, as lung density fell to 0.35 +/- 0.01 g/ml, there was a further decline in velocity to 69.6 +/- 4.6 m/s. High-frequency sound was attenuated as lung density decreased from 1.0 to 0.5 g/ml, with little change thereafter down to a density of 0.35 +/- 0.01 g/ml. We conclude that both the velocity of audible sound through the lung and the degree to which high-frequency sound is attenuated in the lung provide information on the degree of inflation of the isolated fetal lung, particularly at high lung densities. If studies of sound transmission through the lung in the intact organism were to confirm these findings, the acoustic properties of the lung could provide a means for monitoring lung aeration during mechanical ventilation of newborn infants.     

Volume and sound velocity changes accompanying the -helix to -form and coil to -helix transitions in aqueous solution

The volume increment per amino acid residue for the α-helix to β-form transition of uncharged poly-L -lysine in aqueous solution was 3.8 ml in water and 4.3 ml in 0.2M and 1M NaBr solutions at 26°C, respectively. The sound velocity of the polymer solution was greater with the β-helix than with the β-form, but the difference was less in dilute salt solutions and disappeared in 1 or 2M NaBr solution. Thus, the β poly-L -lysine solution was slightly more compressible than the α-polymer solution, but this difference was diminished with increasing salt concentration. Both the volume change and the change in adiabatic compressibility of the polymer solution suggest that hydrophobic interactions among the lysyl groups in the β-form reduce the amount of “icebergs” surrounding the polymer molecules as compared with the amount originally present with the α-helix. The coil-to-helix transition of poly-L -glutamic acid in aqueous solution was also accompanied by a decrease in sound velocity. This can be attributed to the reduction of the water of hydration which is less compressible than free water.     

Ultrasonic study of melittin effects on phospholipid model membranes.

Low dose effects of melittin on dilute suspensions of dipalmitoylphosphatidylcholine multilamellar vesicles are investigated by studying the acoustic properties of the system. The temperature dependencies of sound velocity and absorption have been measured at 7.2 MHz in the temperature range of 20-55 degrees C, for different peptide/lipid molar ratios, R. The most pronounced effects were observed at R = 5 x 10(-3), in the vicinity of the pretransition, with a simultaneous increase in sound absorption and velocity. This indicates that melittin affects the polar head group region of the bilayer resulting in a decrease in mobility of the polar head groups. A nonmonotonic dependence of the main transition temperature, with an initial decrease followed by an increase as melittin is added, is interpreted as a consequence of a destabilizing action of the interfaces between mellitin-affected clusters and the unaffected phase.     

Spatial and spectral dependence of the auditory periphery in the northern leopard frog

We investigated directionalities of eardrum vibration and auditory nerve response in anesthetized northern leopard frogs (Rana pipiens pipiens). Simultaneous measures of eardrum velocities and firing rates from 282 auditory nerve fibers were obtained in response to free-field sounds from eight directions in the horizontal plane. Sound pressure at the external surface of the ipsilateral eardrum was kept constant for each presentation direction (± 0.5 dB). Significant effects of sound direction on eardrum velocity were shown in 90% of the cases. Maximum or minimum eardrum velocity was observed more often when sounds were presented from the lateral and posterior fields, or from the anterior and contralateral fields, respectively. Firing rates of 38% of the fibers were significantly affected by sound direction and maximum or minimum firing rate was observed more frequently when sounds were delivered from the lateral fields, or from the anterior and contralateral fields, respectively. Directionality patterns of eardrum velocity and nerve firing also vary with sound frequency. Statistically significant correlation between eardrum velocity and nerve fiber firing rate was demonstrated in only 45% of the fibers, suggesting that sound transmission to the inner ear through extratympanic pathways plays a non-trivial role in the genesis of directionality of auditory nerve responses.Abbreviations CF characteristic frequency - SVL snout-vent length - TM tympanic membrane     

Acoustic microscopy of cultured cells

The scanning acoustic microscope (SAM) allows one to measure mechanical parameters of living cells with high lateral resolution. By analyzing single acoustic images’ sound attenuation and sound velocity, the latter corresponding to stiffness (elasticity) of the cortical cytoplasm can be determined. In this study, measurements of stiffness distribution in XTH-2 cells were compared with the organization of F-actin and microtubules. Single XTH-2 cells exhibit relatively high stiffness at the free margins; toward the cell center this value decreases and reaches a sudden minimum where the slope of the surface topography enlargens at the margin of the dome-shaped cell center. The steepness of the increase in slope is linearly related to the decrease in sound velocity at this site. Thus, a significant determinant of cell shape is paralleled by an alteration of stiffness. In the most central parts, no interferences could be distinguished, therefore, this region had to be excluded from the calculations. Stiffness distribution roughly coincided with the distribution of F-actin, but no correlation to microtubule arrangement was found. Following the treatment of XTH-2 cells with ionomycin in the presence of calcium (in the culture medium), the cell cortex first contracted as indicated by shape changes and by a marked increase in stiffness (deduced from sound velocity). This contraction phase was followed by a phase of microtubule and F-actin disassembly. Concomittantly, sound velocity decreased considerably, indicating the loss of elasticity in the cell cortex. No structural equivalent to sound attenuation has been identified.     

Acoustic microscopy of cultured cells. Distribution of forces and cytoskeletal elements.

The scanning acoustic microscope (SAM) allows one to measure mechanical parameters of living cells with high lateral resolution. By analyzing single acoustic images' sound attenuation and sound velocity, the latter corresponding to stiffness (elasticity) of the cortical cytoplasm can be determined. In this study, measurements of stiffness distribution in XTH-2 cells were compared with the organization of F-actin and microtubules. Single XTH-2 cells exhibit relatively high stiffness at the free margins; toward the cell center this value decreases and reaches a sudden minimum where the slope of the surface topography enlargens at the margin of the dome-shaped cell center. The steepness of the increase in slope is linearly related to the decrease in sound velocity at this site. Thus, a significant determinant of cell shape is paralleled by an alteration of stiffness. In the most central parts, no interferences could be distinguished, therefore, this region had to be excluded from the calculations. Stiffness distribution roughly coincided with the distribution of F-actin, but no correlation to microtubule arrangement was found. Following the treatment of XTH-2 cells with ionomycin in the presence of calcium (in the culture medium), the cell cortex first contracted as indicated by shape changes and by a marked increase in stiffness (deduced from sound velocity). This contraction phase was followed by a phase of microtubule and F-actin disassembly. Concomittantly, sound velocity decreased considerably, indicating the loss of elasticity in the cell cortex. No structural equivalent to sound attenuation has been identified.     

Differential pulse polarography: a method of directly measuring uptake of metal ions by live bacteria without separation of biomass and medium

Abstract The technique of differential pulse polarography is shown here for the first time to be applicable to monitoring directly the uptake of metal ions from solution by live bacteria in the chamber of the polarograph. The potential at which the polarographic current peak is observed is characteristic of the metal, whereas peak height is proportional to metal concentration. Adding solutions of Cd(II) or Zn(II) to a suspension of Pseudomonas cepacia in 50 mM Hepes buffer (pH 7.4) in the chamber gave polarographic peaks of lower amplitude than those observed when these metal solutions were added to buffer alone, due to metal binding or uptake by cells. Langmuir plots gave binding capacities of 0.13 and 0.20 mmol metal (Dd or Zn, respectively) per g (dry weight) biomass. Ni(II) uptake was biphasic. Metal uptake increased with pH. The value of polarography for rapid assessment of metal removal by cells and the ability to measure uptake from multi-metal solutions is demonstrated.     

Raman spectroscopic studies on the interaction between counterion and polyion

The interaction between alkali metal ions and the polyacrylate ion was investigated by means of Raman spectroscopy. in comparison with the Raman spectra of propionate salts. The Raman bands due to the metal-oxygen bond were not apparent and no significant difference was observed among the Raman spectra of several univalent salts of polyacrylate. except in the case of the lithium salt. The apparent degree of dissociation of lithium polyacrylate, as determined from the relative intensity of a specific band characteristic of the carboxylate ion, was lower than those of the other alkali metal salts. It is concluded from the Raman data that the electrostatic interaction between counterions and a polyion is not specifically modified by forces of a nonionic nature. Moreover, it is pointed out that the local conformation of polyacrylate changes gradually with the degree of neutralization, but that the change is not like a conformational transition between globular and random coil forms.     

Effect of cation and anion of an electrolyte on apparent molar volume, isentropic compressibility and refractive index of glycine in aqueous solutions

Experiments at 298.15 K have been performed to measure the density, velocity of sound and refractive index in three water+glycine+electrolyte systems. The electrolytes studied were KCl, KNO3 and NaNO3. The values of apparent molar volume and isentropic compressibility of glycine in aqueous electrolyte solutions were calculated from the measured data. The results obtained in this study and those reported previously for water+glycine+NaCl system have been comparatively studied. The results show that the nature of both the cation and the anion of an electrolyte influence the behaviour of glycine in aqueous solutions. For all four electrolytes studied, the comparison shows a positive volume transfer for glycine from an electrolyte solution to a more concentrated solution of the same electrolyte. The results also show a negative apparent isentropic compressibility for glycine in the presence of the electrolytes studied. These effects indicate that the volume of a glycine molecule is larger in solutions with higher electrolyte concentration and the water molecules around the glycine molecules are less compressible than the water molecules in the bulk solution. These effects were attributed to the doubly charged behaviour of glycine and to the formation of physically bonded ion-pairs between the charged groups of glycine and the cation and the anion of the electrolyte.     

Oligomeric states of the detergent-solubilized human serum paraoxonase (PON1)

Human plasma paraoxonase (HuPON1) is a high density lipoprotein (HDL)-bound enzyme exhibiting antiatherogenic properties. The molecular basis for the binding specificity of HuPON1 to HDL has not been established. Isolation of HuPON1 from HDL requires the use of detergents. We have determined the activity, dispersity, and oligomeric states of HuPON1 in solutions containing mild detergents using nondenaturing electrophoresis, size exclusion chromatography, and cross-linking. HuPON1 was active whatever its oligomeric state. In nonmicellar solutions, HuPON1 was polydisperse. In contrast, HuPON1 exhibited apparent homogeneity in micellar solutions, except with CHAPS. The enzyme apparent hydrodynamic radius varied with the type of detergent and protein concentration. In C(12)E(8) micellar solutions, from sedimentation velocity, equilibrium analytical ultracentrifugation, and radioactive detergent binding, HuPON1 was described as monomers and dimers in equilibrium. A decrease of the detergent concentration shifted this equilibrium toward the formation of dimers. About 100 detergent molecules were associated per monomer and dimer. The assembly of amphiphilic molecules, phospholipids in vivo, in sufficiently large aggregates could be a prerequisite for anchoring of HuPON1 and then allowing stabilization of the enzyme activity. Changes of HDL size and shape could strongly affect the binding affinity and stability of HuPON1 and result in reduced antioxidative capacity of the lipoprotein.