Proteins ionic strength effects

Chrambach this indicates that the effective protein size for gel filtration is larger than the effective size for gel electrophoresis. They concluded that this could not be accounted for by gel swelling, pH, or ionic strength effects. Biefer and Mason [36] found the constant a in Eq. (93) to be 0.93. They measured the conductance of cellulose acetate filter pads with porosities from 0.5 to 0.9 in solutions of 10 M KCl. 

Andrade SM, Costa SMB (2002) Aggregation kinetics of meso-tetrakis(4-sulfonatophenyl) porphine in the presence of proteins temperature and ionic strength effects. J Fluoresc 12 77-82... 

Macroscopic models have been developed that describe the protein and the water as macroscopic dielectric materials. In their simplest form these models use a distance-independent dielectric function, i.e. a simple Coulomb interaction. Others may apply a distance-dependent dielectric function. The more detailed implementatiorrs include a descriptions of the protein-solvent botmdary in terms of solvent accessibihty and ionic-strength effects (Gilson and Honig, 1988). 

It is also important to point out that the direction of the ionic strength effect on rate constants does not always correlate with the protein net charge. Thus, in reactions with FMN [47] and flavodoxin [48], three species of cytochrome C2 having net charges of —7, 0 and -1-2 all show attractive electrostatic interactions during ET with these negatively charged species. The reason for this behavior lies in the fact... 

The theoretical background to classical electrostatics is first reviewed, beginning with the physical basis for the electrostatic response of a protein/solvent system to a charge distribution, and ways of modelling this response. Consistent classical electrostatic frameworks for describing a protein/solvent system are then described. In addition the methods must be able to model temperature, pH and ionic strength effects if these affect the property of interest. Of particular importance is the way one may extract experimentally observable properties from such models. 

Yang, A. and B. Honig. (1994). Structural origins of pH and ionic strength effects on protein stability. Acid denaturation of sperm whale apomyoglobin. J. Mol. Biol. 237 602-14. 

Dithionite is widely employed in biochemistry for the study of electron-transfer proteins, both as a means of preparing the reduced form of the protein and as a kinetic probe into the reactive behavior of the protein. For example, ionic strength effects are used to infer the charge of the reactive site. Indeed, most of the 140 reactions for which 802 rate constants have been reported are for biological molecules [4]. Essentially all of these have relied upon the equilibrium... 

A.-S. Yang and B. Honig, /. Mol. Biol., 237, 602 (1994). Structural Origins of pH and Ionic Strength Effects on Protein Stability. Acid Denaturation of Sperm WTiale Apomyoglobin. 

Turbidimetric titration curves were obtained by successively adding HCl (1 N at first and then 0.1 N as the critical pH was approached) dropwise to a 250 ml solution of protein (1 gl for the individual proteins 3 gl for the EWP added NaCl concentrations of 0, 0.07, and 0.2 M were used to examine ionic strength effects) and PAA (2.5 mg dissolved in 2.5 ml), initially at pH 11.5, until the critical pH, below which association began to take place, was reached. The transmittance at 436 nm (Bausch and Lomb Spectronic 710 spectrophotometer, Rochester, NY) and pH were recorded after each addition. The critical pH was taken as that pH where the turbidity began to rise. Near the critical pH readings did not stabilize, so readings were recorded each minute without further acid addition. 

Klapper 1, R Hagstrom, RFine, K Sharp and B Honig 1986. Focusing of Electric Fields in tire Actir e Sit of CuZn Superoxide Dismutase Effects of Ionic Strength and Amino-Acid Substitution. Proteins Structure, Function and Genetics 1 47-59. 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

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