Proteins surface activity

Antipova, A.S., Semenova, M.G. (1997a). Effect of neutral carbohydrate structure in the set glucose / sucrose / maltodextrin / dextran on protein surface activity at the air-water interface. Food Hydrocolloids, 11, 71-77. 

Antipova, A., Semenova, M., Gauthier-Jacques, A. (1997). Effect of neutral carbohydrate structure on protein surface activity at air-water and oil-water interfaces. In Dickinson, E., Bergenstahl, B. (Eds). Food Colloids Proteins, Lipids and Polysaccharides, Cambridge, UK Royal Society of Chemistry, pp. 245-258. 

In line with the Gibbs adsorption equation (equation 3.33 in chapter 3), the presence of thermodynamically unfavourable interactions causes an increase in protein surface activity at the planar oil-water interface (or air-water interface). As illustrated in Figure 7.5 for the case of legumin adsorption at the n-decane-water interface (Antipova et al., 1997), there is observed to be an increase in the rate of protein adsorption, and also in the value of the steady-state interfacial pressure n. (For the definition of this latter quantity, the reader is referred to the footnote on p. 96.)... 

The presence of a thermodynamically favourable interaction between protein and polysaccharide is commonly associated with a marked decrease in protein surface activity at the air-water or oil-water interface (see Figures 7.5b and 7.15). There is a slower decay in the surface tension for complexes in comparison with the pure protein, and also higher values of the tension in the steady state. Data establishing these trends have been reported for the following biopolymer pairs in aqueous media legumin + dextran and legumin + maltodextrin (Antipova and Semenova,... 

Figure 7.15 Effect of thermodynamically favourable interactions between biopolymers on protein surface activity at the planar oil-water or air-water interface. The surface pressure n reached after 6 hours is plotted against the polysaccharide concentration ( ), legumin (0.001 wt%) + dextran (Mw = 270 kDa) at / -decane-water surface at pH = 7.8 and ionic strength = 0.01 M, (Ay = -0.2 x 105 cm3 mol1) (Pavlovskaya et ah, 1993) ( ), legumin (0.001 wt%) + maltodextrin (MD6, Mw = 102 kDa) at air-water surface at pH = 7.2 and ionic strength = 0.05 M (Ay = - 0.02 x 105 cm3 mol-1) (Belyakova et ah, 1999) (A), legumin (0.001 wt%) + maltodextrin (MD10, Mw = 45 kDa) at air-water surface at pH = 7.2 and ionic strength = 0.05 M (.1 / = - 0.08 x 105 cm3 mol-1) (Belyakova et ah, 1999).

Emulsion Capacity. Enzymatic digestion of proteins beyond 10 min, except the trypsin-treated sample for 30 min, destroyed emulsifying capacity of the flour (Figure 13). Apparently, hydrolysis substantially altered protein surface activity strengths and the ability of the protein to stabilize oil-in-water emulsions. This assumption agrees with earlier work showing decreased emulsion capacity of peanut flour fermented with fungi (27). 

Protein-water interaction plays an important role in the determination and maintenance of the three-dimensional structure of proteins. Water modified the physicochemical properties of proteins. Therefore, protein-water interactions have been the subject of intensive study and have provided significant advances in our understanding of the involvement of water in protein functionality, stability, and dynamics [6]. The thermodynamics of protein-water interaction directly affects dispersibility, wettability, swelling, and solubility of proteins. Surface-active properties of proteins are simply the result of the thermodynamically unfavorable interaction of exposed nonpolar patches of proteins with solvent water. 

Wei et al. [27] examined the role of protein structure in surface tension kinetics at the air-water interface and demonstrated that the intrinsic, conformational stability is an influencing factor in protein surface activity at low bulk concentrations. At high bulk concentrations, surface hydrophobicity was highly correlated with the observed siuface tension kinetics. Surface tension kinetics in this context refers to the rate of change of liquid siuface tension, 7lv> for protein solution in contact with air. 

Proteins, like other macromolecules, can be made into monolayers at the air-water interface either by spreading, adsorption, or specific binding. Proteins, while complex polymers, are interesting because of their inherent surface activity and amphiphilicity. There is an increasing body of literature on proteins at liquid interfaces, and here we only briefly discuss a few highlights. 

The second type is a stable dispersion, or foam. Separation can be extremely difficult in some cases. A pure two-component system of gas and liquid cannot produce dispersions of the second type. Stable foams can oe produced only when an additional substance is adsorbed at the liquid-surface interface. The substance adsorbed may be in true solution but with a chemical tendency to concentrate in the interface such as that of a surface-active agent, or it may be a finely divided sohd which concentrates in the interface because it is only poorly wetted by the liquid. Surfactants and proteins are examples of soluble materials, while dust particles and extraneous dirt including traces of nonmisci-ble liquids can be examples of poorly wetted materials. 

In HIC, the hydrophobic interactions are relatively weak, often driven by salts in moderate concentration (I to 2 M), and depend primarily on the exposed residues on or near the protein surface preservation of the native, biologically active state of the protein is an important feature of HIC. Elution can be achieved differentially by decreasing salt concentration or increasing the concentration of polarity perturbants (e.g., ethylene glycol) in the eluent. 

The thioredoxin domain (see Figure 2.7) has a central (3 sheet surrounded by a helices. The active part of the molecule is a Pa(3 unit comprising p strands 2 and 3 joined by a helix 2. The redox-active disulfide bridge is at the amino end of this a helix and is formed by a Cys-X-X-Cys motif where X is any residue in DsbA, in thioredoxin, and in other members of this family of redox-active proteins. The a-helical domain of DsbA is positioned so that this disulfide bridge is at the center of a relatively extensive hydrophobic protein surface. Since disulfide bonds in proteins are usually buried in a hydrophobic environment, this hydrophobic surface in DsbA could provide an interaction area for exposed hydrophobic patches on partially folded protein substrates. 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

Recently, peptoid-based mimics of both SP-C and SP-B have been designed to adopt helical secondary structures, and also mimic (to varying degrees) the sequence patterning of hydrophobic and polar residues found in the natural surfactant proteins. Peptoid-based SP-C mimics of up to 22 monomers in length, were synthesized and characterized by in vitro experimental methods [67, 68] (Fig. 1.8). The secondary structure of all molecules was assessed by circular dichroism and found to be helical. The surface activities of these peptoids, in comparison to the actual SP peptides described above, were characterized by surfactometry using... 

Comparative study of LB films of cytochrome P450 wild type and recombinant revealed similar surface-active properties of the samples. CD spectra have shown that the secondary structure of these proteins is practically identical. Improved thermal stability is also similar for LB films built up from these proteins. Marked differences for LB films of wild type and recombinant protein were observed in surface density and the thickness of the deposited layer. These differences can be explained by improved purity of the recombinant sample. In fact, impurity can disturb layer formation, preventing closest packing and diminishing the surface density and the average monolayer thickness. Decreased purity of... 

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