Adsorbed protein general properties

We have not developed this general scheme into a functional immunoassay for estriol at the clinical level because of the inadequate detection limit, unlike previous secticms. However, we have explored those features of such an assay that would be applicable to other analytes. It is particularly important with an electrode such as the DME that readily adsorbs proteins to demonstrate that the results obtained are not artifactual. It is also important to determine whether the labeled Ag has radically different properties from unlabeled Ag that might be detrimental to assay development. 

The behavior of protein molecules at solid surfaces is very complex. The interaction between the surface and the protein is determined both by the nature of the protein, the surface and the medium outside the surface. The situation is further complicated by the fact that exchange reactions between protein molecules of the same or different kinds take place on the surface. Except for these exchange reactions most protein molecules appear to be irreversibly adsorbed. Although the details of the interaction between protein molecules and surfaces are not known it is assumed that general properties of the surface and the protein such as hydrophobicity, charge density, ion binding, hydration etc. are involved. For reviews, see e.g (21.35-37). 

The effect of chain length on surface tension arises from the fact that, as the hydrophobicity increases with each -CH2- group, the amphiphile molecule adsorbs more at the surface. This will thus be a general trend in more complicated molecules also, such as proteins and other polymers. In proteins, the amphiphilic property arises from the different kinds of amino acids (25 different amino acids). Some amino acids have lipophilic groups (such as phenylalanine, valine, leucine, etc.), while others have hydrophilic groups (such as glycine, aspartic acid, etc.) (Figure 3.4). 

It has been known that adsorption kinetics and/or thermodynamics of proteins depend on the electric or electrochemical properties of solid supports on which the proteins are adsorbed. This has led us to elucidate the effects of electrode potential on the adsorption behavior of avidin on the electrode surface. For this purpose, the electrode potential of a Pt electrode was varied systematically in the range of -0.5-+2.0 V in an avidin solution (pH 7.4). Although the data was somewhat scattered, a general trend was observed that the adsorption of avidin is suppressed by the application of a positive potential (+1.0-+2.0 V). This may be originating from the fact that avidin is a basic protein and has net positive charges in the solution of neutral pH. In the potential range tested, no significant acceleration in the adsorption was induced. 

In general, surface activity behaviour in food colloids is dominated by the proteins and the low-molecular-weight surfactants. The competition between proteins and surfactants determines the composition and properties of adsorbed layers at oil-water and air-water interfaces. In the case of mixtures of proteins with non-surface-active polysaccharides, the resulting surface-activity is usually attributed to the adsorption of protein-polysaccharide complexes. By understanding relationships between the protein-protein, protein-surfactant and protein-polysaccharide interactions and the properties of the resulting adsorbed layers, we can aim to... 

Apparently, no single factor can be used to predict the process of adsorption there are always several different properties of protein and adsorbent that determine the protein-surface interaction. As a summary, the following general guidelines can be given ... 

A fibrin clot containing adsorbed plasmin inhibitors is difficult to define in a chemical or physical sense. Generally, when enzyme reactions occur at surfaces, the porosities and adsorption properties erf which are variable, the reproducibility of enzyme assay methods is questionable. The proteinoses, to which belong the most important pharmaceutical enzymes, may present some difficulties when natural substrates (protein ) are prescribed. Here, the application of a parallel run with a reference standard is recommended. 

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