THE COLLOIDAL BEHAVIOR OF SERUM GLOBULIN

1. The globulin prepared from ox serum by dilution and precipitation with carbon dioxide has been found, by electrometric titration experiments, to behave like an amphoteric electrolyte, reacting stoichiometrically with acids and bases. 2. The potential difference developed between a solution of globulin chloride, phosphate, or acetate and a solution of the corresponding acid, free from protein, separated from the globulin by a collodion membrane, was found to be influenced by hydrogen ion concentration and salt concentration in the way predicted by Donnan''s theory of membrane equilibrium. In experiments with sodium globulinate and sodium hydroxide it was found that the potential difference could be similarly explained. 3. The osmotic pressure of such solutions could be qualitatively accounted for by the Donnan theory, but exhibited a discrepancy which is explicable by analogy with certain experiments of Loeb on gelatin. 4. The application of Loeb''s theory of colloidal behavior, which had previously been found to hold in the case of gelatin, casein, egg albumin, and edestin, has thus been extended to another protein, serum globulin.     

Design of a system for the accelerated loading of heart valve prostheses

In this paper an equipment is described for the loading of heart valve prostheses under physiological pressure conditions at a frequency of 10 Hz. The system consists essentially of two reservoirs between which a housing is mounted for holding the valve prosthesis. The reservoirs are partly filled with liquid. The physiological pressure variation across the valve is obtained by pressure control within the two reservoirs. A phase difference between the pressures in the two reservoirs compensates for the mass-inertia effects which normally occur at these high frequencies. The system without a valve has been analysed on the basis of simplified relationships between pressure and flow. The predicted values for the phase difference between the flow and the pressure curves within the valve housing, have been verified experimentally for various values of phase difference and amplitude ratios of the pressure variations within the reservoirs. The agreement between theory and experiment is fair. For the system with a valve the experimentally observed patterns closely resemble the theoretically predicted ones. From experiments with a Bj?rk-Shiley ( 21ABP ) and a Hancock (242-A21) valve prosthesis it is concluded that the valves open and close completely and that the pressure and flow patterns around the valves mimic the essential features of the in-vivo signals.     

A new view of convective-diffusive transport processes in the arterial intima

In this paper a new theoretical framework is presented for analyzing the filtration and macromolecular convective-diffusive transport processes in the intimal region of an artery wall with widely dispersed macromolecular cellular leakage sites, as proposed in the leaky junction-cell turnover hypothesis of Weinbaum et al. In contrast to existing convection-diffusive models, which assume that the transport is either 1-D, or convection is primarily in a direction normal to the endothelial surface, the present model considers for the first time the nonuniform subendothelial pressure field that arises from the different hydraulic resistances of normal and leaky endothelial clefts and the special role of the internal elastic lamina (IEL) in modulating the horizontal transport of macromolecules after they have passed through the leaky clefts of cells that are either in mitosis or demonstrate IgG labeling. The new theory is able to quantitatively explain the growing body of recent experiments in which an unexpectedly rapid early-time growth of the leakage spot has been observed and the longer time asymptotic behavior in which the leakage spot appears to approach an equilibrium diameter. The new theory also predicts the observed doubling in macromolecular permeability between EBA labeled blue and white areas when the frequency of leakage sites is doubled. This frequency for doubling of permeability, however, is an order of magnitude smaller than predicted by the author's previous model, Tzeghai et al., in which only convection normal to the endothelial surface was considered and the pressure was uniform in the intima. The longer time model predictions are used to explain the time scale for the formation of liposomes in subendothelial tissue matrix in animal feeding experiments where it has been observed that the extracellular lipid concentration rises sharply prior to the entry of monocytes into the intima.     

A theory of cell hydration governed by adsorption of water on cell proteins rather than by osmotic pressure

It is postulated that cell hydration is governed by adsorption of water on cell proteins in accord with the Bradley adsorption isotherm, and that the action of a solute in the surrounding solution is to lower the vapor pressure of the solution so that cell water adsorption is decreased by moving down the Bradley isotherm. From these concepts, it is derived that cell volume (V) should be related to solute concentration (x) by the equationV=−E log₁₀ x+F whereE andF are constants which are independent of type of solute. For a non-adsorbed solute this agrees well with experimental data. For solutes which are adsorbed by cell proteins, a correction in the above equation may be necessary at higher solute concentrations, which is shown to be compatible with various experimental data. The types of experiments which are generally used to support the osmotic pressure theory of cell hydration agree equally well with the adsorption theory. The virtue of the adsorption theory is that, unlike the osmotic pressure theory of cell swelling, it is compatible with permeability of the cell membrane to solutes, which has been experimentally observed for various solutes. The opinions and conclusions contained in this report are those of the author. They are not to be construed as necessarily reflecting the views or the endorsement of the Navy Department.     

Fluid Dynamics Simulating Experiment of Pressure Gradient for Assimilate Translocation in Sieve Tubes

According to the similitude theory of fluid mechanics, a pressure-driven experiment in a sieve tube model has been performed. The relationships between the pressure gradient and the transport velocities at the various diameters of sieve pore have been obtained. The experimental data were compared with the theoretical prediction based on the poiseuille equation. The result shows that the pressure gradient required for translating the assimilate is directly proportional to the translating velocity, which agrees with Poiseuille equation. However, the resistance of the sieve plate to flow is much more than that estimated by the previous theory. Even though the translating velocity is a normal level and the diameter of the sieve tube is a typical size, the pressure gradient required for flow is about 1 bar/m. It will increase sharply with the decrease of the diameter of sieve pore. The ratios of the pressure gradients measured in the test to that predicted by Poiseuille equation are about 2–4 for the five kinds of diameters of Sieve pore. Additionally, a simulating test of the pores being partly plugged has been performed. The result shows that the pressure gradients measured are greatly beyond the range that may be kept in plants. This study will be helpful to assess Munch hypothesis.     

Hydration structure,thermodynamics, and functions of protein studied by the 3D-RISM theory

The three-dimensional reference interaction site model (3D-RISM) theory is a molecular theory of solvation, which has been developed recently. Unlike the conventional statistical-mechanical theories of liquids, the applications of which are limited to rather simple systems, the new theory has been demonstrating great success in predicting the hydration structure and thermodynamic quantities of protein. Here, we review the recent applications of the 3D-RISM theory to some subjects concerning protein hydration: detecting water molecules in protein cavities, the pressure effects on protein conformation in terms of the partial molar volume, and the pressure reversal of anesthesia. These results demonstrate the outstanding capability of the theory for investigating various issues in biochemistry and biophysics.     

Can pyrene probes be used to measure lateral pressure profiles of lipid membranes? Perspective through atomistic simulations

The lateral pressure profile of lipid bilayers has gained a lot of attention, since changes in the pressure profile have been suggested to shift the membrane protein conformational equilibrium. This relation has been mostly studied with theoretical methods, especially with molecular dynamics simulations, since established methods to measure the lateral pressure profile experimentally have not been available. The only experiments that have attempted to gauge the lateral pressure profile have been done by using di-pyrenyl-phosphatidylcholine (di-pyr-PC) probes. In these experiments, the excimer/monomer fluorescence ratio has been assumed to represent the lateral pressure in the location of the pyrene moieties. Here, we consider the validity of this assumption through atomistic molecular dynamics simulations in a DOPC (dioleoylphosphatidylcholine) membrane, which hosts di-pyr-PC probes with different acyl chain lengths. Based on the simulations, we calculate the pyrene dimerization rate and the lateral pressure at the location of the pyrenes. The dimerization rates are compared with the results of di-pyr-PC probes simulated in vacuum. The comparison indicates that the lateral pressure is not the dominant determinant of the excimer/monomer fluorescence ratio. Thus, the results do not support the usage of di-pyr-PC molecules to measure the shape of the lateral pressure profile. We yet discuss how the probes could potentially be exploited to gain qualitative insight of the changes in pressure profile when lipid composition is altered.     

Application of a Theory for Circumnutations to Geotropic Movements

From a previously published theory (Israelsson and Johnsson 1967) for circumnutations in Helianthus annuus it is possible to predict the geotropical curvatures of the hypocotyls. This extension of the theory is given in the present paper and some geotropical experiments are performed and discussed. The agreement between the theory and the experiments has been verified in the case of gravitational stimulation during relatively short stimulation periods, in the case of continuous gravitational stimulation, etc. Restrictions in the proposed model are discussed.     

Measurement of oscillatory flow pressure gradient in an elastic artery model

In vitro experiments were conducted to measure the oscillatory flow pressure gradient along an elastic tube in order to assess the recent nonlinear theory of Wang and Tarbell. According to this theory, in an elastic tube with oscillatory flow, the mean (time-averaged) pressure gradient cannot be calculated using Poiseuille's law. The effect of wall motion creates a nonlinear convective acceleration, and an induced mean pressure gradient is required to balance the convective acceleration. The induced mean pressure gradient depends on the diameter variation over a cycle, the pulsatility and unsteadiness of the flow, and the phase difference between the pressure wave form and the flow wave form. The amplitude of the pressure gradient also depends on these parameters and may deviate significantly from Womersley's rigid tube theory. A flow loop was constructed to produce oscillatory flow in an elastic tube. Flow wave forms were measured with an ultrasonic flow probe, and ultrasonic diameter crystals were used to measure wall movement. A special device for pressure drop measurement was constructed using Millar catheter tip transducers to obtain both forward and backward pressure drops that were then averaged. This averaging method eliminated the static error of the pressure transducers. The pressure-flow phase angle was varied by clamping a distal elastic section at various locations. Pressure gradients were obtained for a range of phase angles between −55 ° and +49 °. The mean and amplitude of the measured pressure gradient were compared to theoretical values. Both positive and negative induced mean pressure gradients were measured over the range of phase angles. The measured pressure gradient amplitudes were always lower than predicted by Womersley's rigid tube theory. The experimental means and amplitudes are in good agreement with the elastic tube theoretical values. Thus, the experiments verify the theory of Wang and Tarbell.     

On the transmission of external pressure fluctuations to the cerebrospinal fluid

A theory has been formulated to explain the manner in which external pressure fluctuations are transmitted to the cerebrospinal fluid (CSF). The theory is based upon a three-compartment model which consists of the cerebral ventricles, the basal cisterns and spinal subarachnoid space, and the cortical subarachnoid space. The external pressure disturbance is represented by a Fourier series summed over the frequency ω. The mathematical analysis leads to a time constant τ which depends upon the compliances of the spinal region and sources of external pressure fluctuations, the rate of CSF absorption and the rate of fluid transfer between compartments. For arterial pulsations where ωτ ? 1, the theory is in accord with the experimental observations that (i) the arterial and CSF pulse waves are nearly identical in shape, and (ii) the amplitude of the CSF pulse wave increases with intracranial pressure. Moreover, it predicts that the amplitude of the wave will be larger in the spinal region than in the ventricles. The theory also accounts for the observation of one per minute pulse waves observed in hydrocephalic patients with decreased absorption rates.     

Statistical mechanical analysis of Raman spectroscopic order parameter changes in pressure-induced lipid bilayer phase transitions.

The statistical mechanical cluster theory of Fisher as applied by Kanehisa and Tsong to phospholipid bilayers is modified to describe the effects of hydrostatic pressure on the state of an aqueous dispersion of the phospholipid dipalmitoyl phosphatidylcholine. A high pressure Raman scattering cell has been built to obtain the Raman spectra of aqueous dispersions of phospholipids as a function of the applied hydrostatic pressure from 0 to 100 atmospheres. Predicted thermal and pressure-induced phase transitions are compared with an experimentally obtained Raman order parameter derived from the ratio of two bands in the C-H stretching region of the Raman spectrum of the sample. The parameters of the theory are adjusted to obtain a satisfactory fit of the Raman order parameter versus temperature. The theory is then found to give an excellent prediction of the observed pressure dependence of the Raman order parameter with no changes in the adjustable parameters. The implications of the success of the theoretical fit is discussed. Particularly of interest is the rather high value of the critical temperature, Tc, for lipid bilayers which is predicted by the model.     

Thermal stabilities of globular proteins

Statistical thermodynamic theory has recently been developed to account for the stabilities of globular proteins. Here we extend that work to predict the dependence on temperature. Folding is assumed to be driven by solvophobic interactions and opposed by the conformational entropy. The temperature dependence of the solvophobic interaction is taken from the transfer experiments on amino acids by Tanford and Nozaki and on model solutes by Gill and Wads?. One long-standing puzzle has been why proteins denature upon heating, since the solvophobic force to fold strengthens with increasing temperature. This is resolved by the theory, which predicts two first-order phase transitions. "Cold denaturation" is driven principally by the weakening of the solvophobic interaction, but normal denaturation is driven principally by the gain of conformational entropy of the chain. Predictions of the thermodynamic state functions are in reasonable agreement with the calorimetric experiments of Privalov and Khechinashvili. Comparison of the theory with experiments suggests that there may be an additional enthalpic driving force toward folding which is not due to the solvophobic interactions.     

THE COLLOIDAL BEHAVIOR OF EDESTIN

1. It has been shown by titration experiments that the globulin edestin behaves like an amphoteric electrolyte, reacting stoichiometrically with acids and bases. 2. The potential difference developed between a solution of edestin chloride or acetate separated by a collodion membrane from an acid solution free from protein was found to be influenced by salt concentration and hydrogen ion concentration in the way predicted by Donnan''s theory of membrane equilibrium. 3. The osmotic pressure of such edestin-acid salt solutions was found to be influenced by salt concentration and by hydrogen ion concentration in the same way as is the potential difference. 4. The colloidal behavior of edestin is thus completely analogous to that observed by Loeb with gelatin, casein, and egg albumin, and may be explained by Loeb''s theory of colloidal behavior, which is based on the idea that proteins react stoichiometrically as amphoteric electrolytes and on Donnan''s theory of membrane equilibrium.     

Parallel-plate fluid flow systems for bone cell stimulation

Bone responds to changes in its mechanical environment, but the mechanisms by which it does so are poorly understood. One hypothesis of mechanosensing in bone states that osteocytes can sense the flow of fluid through the canalicular system. To study this in vitro a number of fluid flow devices have been designed in which cells are placed between parallel plates in sealed chambers. Fluid flows through the chambers at controlled rates, most commonly driven by a peristaltic pump. In addition to fluid flow, high pressures have been observed in these chambers, but the effect of this on the cellular responses has generally been ignored or considered irrelevant, something challenged by recent cellular experiments using pressure only. We have, therefore, devised a system in which we can considerably reduce the pressure while maintaining the flow rate to enable study of their effects individually and in combination. As reducing pressure also reduces the risk of leaks in flow chambers, our system is suitable for real-time microscopical experiments. We present details of the new systems and of experiments with osteoblasts to illustrate the effects of fluid flow with and without additional pressure on the translocation of β-catenin to the nucleus.     

Selective pressures on genomes in molecular evolution

We describe the evolution of macromolecules as an information transmission process and apply tools from Shannon information theory to it. This allows us to isolate three independent, competing selective pressures that we term compression, transmission, and neutrality selection. The first two affect genome length: the pressure to conserve resources by compressing the code, and the pressure to acquire additional information that improves the channel, increasing the rate of information transmission into each offspring. Noisy transmission channels (replication with mutations) give rise to a third pressure that acts on the actual encoding of information; it maximizes the fraction of mutations that are neutral with respect to the phenotype. This neutrality selection has important implications for the evolution of evolvability. We demonstrate each selective pressure in experiments with digital organisms.     

Xylem water transport: is the available evidence consistent with the cohesion theory?

Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m⁻¹. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants.     

Flow separation, an important mechanism in the formation of mean pulmonary pressure during high-frequency oscillation

Mean pressures within the lungs and lung volume, respectively, are clinically important parameters. During ventilation by way of high-frequency oscillation (HFO), these parameters have been shown to be strongly frequency dependent. To identify mechanisms leading to mean pressure formation during HFO, findings of the theory of stationary flow were extended to oscillatory flow by a quasi-stationary approach. To confirm the theoretical findings, in-vitro experiments on HFO-models were performed. Flow separation was found to be an important mechanism in the formation of mean pressure. Flow separation causes a significant flow resistance, which may be distinctly different for in- and outflow. During oscillatory flow, a mean pressure difference thus results. This mechanism is of particular importance in bifurcations, which are present in the HFO-circuit as well as in the airways. With the direction-dependent flow separation, a general mechanism was found, which accounts for differing mean pressure values within the lungs with different HFO-circuits. This mechanism also contributes to interregionally different mean pressure values within the lungs.