Surface Adsorption Behavior of Proteins at Ambient Temperature

Surface Adsorption Behavior of Proteins at Ambient Temperature 

The results of electrochemical experiments that have been focused on the elucidation of the conformational behavior of proteins at the electrode surface, particularly in comparison with their conformational behavior in the bulk solution, will be discussed in this section. The purpose is to determine whether electrochemical techniques are able to probe the structure-function relationships of these macromolecules in such a way as to provide a different and complementary perspective which may help unravel the complex behavior of these very important biological compounds. The discussion will be focus on three proteins whose three-dimensional structures have been well characterized by X-ray diffraction and whose interfacial behavior has been extensively investigated by a variety of techniques. Comparisons of the results obtained for these well-characterized proteins from electrochemical experiments under similar experimental conditions provide a basis for evaluating these electrochemical methods in relation to some of the more traditional techniques described in Section II. 

The three globular proteins jS-lactoglobulin A, hen egg-white lysozyme, and bovine pancreatic ribonuclease A all have similar molecular weights. The whey protein jff-lactoglobulin has been the subject of numerous publications owing to the important role it plays in the fouling of metal surfaces and in the formation and stabilization of dairy foams and emulsions. The structure, determined by X-ray crystallography, consists 

From the surface charge densities, 0ads Ihe number of electrons transferred, n, calculated from the number of carboxyl groups present on the protein on the basis of a two-electron-transfer process per carboxyl group, the molar mass of the protein, M, and the Faraday constant, F, an upper limit of the surface concentration, F, may be calculated  

Similarly for each of the other proteins, cyclic voltammograms were recorded after each addition of an aliquot of protein to the buffer solution in the electrochemical cell. The surface charge density was measured over the region which normally corresponds to a monolayer of OH during oxide formation in aqueous solutions, to the anodic end potential of 0.4 V (vs. SCE). Since this is also the rest potential of lysozyme on platinum, the surface charge densities measured to this anodic end potential may reflect the adsorption of a monolayer of protein and allow correlation with results from other experimental techniques. The calculated values of 7 for the three proteins considered in these studies are shown in Fig. 5. Plateau values in surface charge densities can be seen at low bulk concentrations 

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