Proteins surface energy

Separations in hydrophobic interaction chromatography have been modeled as a function of the ionic strength of the buffer and of the hydrophobicity of the column, and tested using the elution of lysozyme and ovalbumin from octyl-, butyl- and phenyl-Sepharose phases.2 The theoretical framework used preferential interaction analysis, a theory competitive to solvophobic theory. Solvophobic theory views protein-surface interaction as a two-step process. In this model, the protein appears in a cavity in the water formed above the adsorption site and then adsorbs to the phase, with the free energy change... 

The use of biological materials as coatings for piezoelectric crystals was first demonstrated by Shons et al. [237], who immobilized bovine serum albumin (BSA) on a crystal precoated with a 30% solution of Nyebar C, a low-surface energy plastic. The rationale of using this solution as the coating material is that proteins adsorbed on low-energy surfaces retain their antigenic properties. Exposure of the BSA-coated crystal to a solution... 

Discuss with your neighbor how protein adsorption can still be spontaneous (AG < 0), even though some of these processes are endothermic (AH > 0). Look up values for the solid surface energies of the two substrates in Appendix 4 (you may have to select similar materials, but this is sufficient for these purposes). How do these enthalpies compare in magnitude to the respective surface energies ... 

Figure 2.38 Influence of substrate surface energy on cell spreading with preadsorbed serum proteins (solid line) and without (dashed line). Reprinted, by permission, from J. M. Schakemaad Cells Their Surfaces and Interactions with Materials, in Biomaterials Science An Introduction to Materials in Medicine, B. D. Ratner, A. S. Hoffman, F. J. Schoen, and J. E. Lemons, p. 144. Copyright 1996 by Academic Press.

How can each step in this complex assembly process set the stage for the next step Apparently the structure of each newly synthesized protein monomer is stable only until a specific interaction with another protein takes place. The binding energy of this interaction is sufficient to induce a conformational alteration that affects a distant part of the protein surface and generates complementarity toward a binding site on the next protein that is to be added. Every one of the baseplate proteins must have such self-activating properties Sometimes proteolytic cleavage of a subunit is required. If it occurs at an appropriate point in the sequence it provides thermodynamic drive for the assembly process. 

In TIRF protein adsorption experiments, it is desirable to correlate the intensity of excited fluorescence with excess protein concentration at the interface. Such an adsorbed layer is often in equilibrium with bulk-nonadsorbed protein molecules which are also situated inside the evanescent volume and thus contributing to the overall fluorescence. Various calibration schemes were proposed, using external nonadsorbing standards40,154 , internal standard in a form of protein solution together with a type of evanescent energy distribution calculation 154), and independent calibration of protein surface excess 155). Once the collected fluorescence intensity is correlated with the amount of adsorbed protein, TIRF can be applied in the study of various interactions between surface and protein. 

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