Biomedical subjects

S I Sandler

Publications and source records attributed to S I Sandler.

4 recordsLinked to original sources

PubMed2002

Thermodynamics and bioenergetics.

Bioenergetics is concerned with the energy conservation and conversion processes in a living cell, particularly in the inner membrane of the mitochondrion. This review summarizes the role of thermodynamics in understanding the coupling between the chemical reactions and the transport of substances in bioenergetics. Thermodynamics has the advantages of identifying possible pathways, providing a measure of the efficiency of energy conversion, and of the coupling between various processes without requiring a detailed knowledge of the underlying mechanisms. In the last five decades, various new approaches in thermodynamics, non-equilibrium thermodynamics and network thermodynamics have been developed to understand the transport and rate processes in physical and biological systems. For systems not far from equilibrium the theory of linear non-equilibrium thermodynamics is used, while extended non-equilibrium thermodynamics is used for systems far away from equilibrium. All these approaches are based on the irreversible character of flows and forces of an open system. Here, linear non-equilibrium thermodynamics is mostly discussed as it is the most advanced. We also review attempts to incorporate the mechanisms of a process into some formulations of non-equilibrium thermodynamics. The formulation of linear non-equilibrium thermodynamics for facilitated transport and active transport, which represent the key processes of coupled phenomena of transport and chemical reactions, is also presented. The purpose of this review is to present an overview of the application of non-equilibrium thermodynamics to bioenergetics, and introduce the basic methods and equations that are used. However, the reader will have to consult the literature reference to see the details of the specific applications.

Animals↗

PubMed2000

Phase equilibria in the lysozyme-ammonium sulfate-water system.

Ternary phase diagrams were measured for lysozyme in ammonium sulfate solutions at pH values of 4 and 8. Lysozyme, ammonium sulfate, and water mass fractions were assayed independently by UV spectroscopy, barium chloride titration, and lyophilization respectively, with mass balances satisfied to within 1%. Protein crystals, flocs, and gels were obtained in different regions of the phase diagrams, and in some cases growth of crystals from the gel phase or from the supernatant after floc removal was observed. These observations, as well as a discontinuity in protein solubility between amorphous floc precipitate and crystal phases, indicate that the crystal phase is the true equilibrium state. The ammonium sulfate was generally found to partition unequally between the supernatant and the dense phase, in disagreement with an assumption often made in protein phase equilibrium studies. The results demonstrate the potential richness of protein phase diagrams as well as the uncertainties resulting from slow equilibration.

Ammonium Sulfate↗

PubMedDate not supplied

Polymer fractionation in aqueous two-phase polymer systems.

We consider the effects of the addition of poly(ethylene glycol) (PEG) of different molecular weights to aqueous two-phase system of PEG 8000 and dextran 500. The first purpose of this study was to determine the molecular weight partitioning of the polymers themselves so that, for example, aqueous two-phase separations using affinity ligands can be improved. The second purpose was to examine whether this molecular weight partitioning could be predicted by using solution thermodynamic models so that it would be possible to optimize affinity partitioning without extensive laboratory work. Experimentally, we find that, by increasing the PEG concentration of any molecular weight in the feed, the high molecular weight PEG concentration in the dextran-rich phase is reduced. This observation can be used to reduce the loss of expensive ligated PEG used in affinity partitioning. Further, there is generally good agreement between our experimental data and the predictions of a solution thermodynamic model.

Dextrans↗

PubMedDate not supplied

Correlation between the osmotic second virial coefficient and the solubility of proteins.

A correlation between the osmotic second virial coefficient and the solubility of proteins is derived from classical thermodynamics to support an empirical relation previously found by Wilson and co-workers (1). The model is based on the equality of fugacities of the protein in the equilibrium phases, with the details of the model depending on the standard state used. The parameters in this model have been fitted to data for several systems, mainly with lysozyme as the protein. The model is found to describe experimental data, with variations in protein concentration, salt type and concentration, temperature, and pH, both qualitatively and quantitatively. Agreement between the model and the experimental data is very good for protein solubilities up to 30 mg/mL. Above this value the model underpredicts the experimental data, probably as a result of multibody interactions that are not included in the model here. Variations of the model parameters with protein type, temperature, pH, and salt type are discussed.

Hydrogen-Ion Concentration↗