Polysaccharides complex formation

Tryptophan 108 is recognized to be an active site in promoting the hydrolysis of 3(l,4)-glycosidic linkages between amino sugar residues in polysaccharide components of the bacterial cell walls. This residue is shown to occupy the cleft as well as trjrptophan 62 and 63, and is in a hydrophobic region. Tryptophan residues 62 and 108 are indispensable for the action of lysozyme, and tryptophan 62 is known to be the only binding site for the complex formation (13). Oxidation of tryptophan-108 is expected... 

McClements, 2006 Anal et al., 2008). Different combinations of proteins and polysaccharides (e.g., P-lactoglobulin + pectin, carrageenan or alginate casein + pectin) have been investigated within the context of multilayer emulsion stabilization (Guzey and McClements, 2006). It seems that the main technical challenge associated with the utilization such complex formation for layer-by-layer emulsion stabilization is the avoidance of bridging flocculation (McClements, 2005, 2006). 

The electrostatic interaction between oppositely charged protein and polysaccharide can be utilized for encapsulation and delivery of hydro-phobic nutraceuticals. As a result of this interaction, we may have either complex coacervation (and precipitation) or soluble complex formation, depending on various factors, such as the type of polysaccharide used (anionic/cationic), the solution pH, the ionic strength, and the ratio of polysaccharide to protein (see sections 2.1, 2.2 and 2.5 in chapter seven for more details) (Schmitt et al, 1998 de Kruif et al., 2004 Livney, 2008 McClements et al, 2008, 2009). The phenomenon of complex... 

It seems that there is probably greater availability of positively charged residues on the adsorbed protein for electrostatic interaction with sulfate groups of the anionic polysaccharide. This could lead to a greater extent of neutralization of dextran sulfate as a result of complex formation, and consequently to a lower thermodynamic affinity of the complexes for the aqueous medium and a lower value of the ( -potential for emulsion droplets in bilayer emulsions. 

Weinbreck, F., Nieuwenhuijse, H., Robijn, G.W., de Kruif, C.G. (2003b). Complex formation of whey protein-exocellular polysaccharide EPS B40. Langmuir, 19, 9404-9410. 

Figure 8.12 illustrates the effect of complex formation between protein and polysaccharide on the time-dependent surface shear viscosity at the oil-water interface for the system BSA + dextran sulfate (DS) at pH = 7 and ionic strength = 50 mM. The film adsorbed from the 10 wt % solution of pure protein has a surface viscosity of t]s > 200 mPa s after 24 h. As the polysaccharide is not itself surface-active, it exhibited no measurable surface viscosity (t]s < 1 niPa s). But, when 10 wt% DS was introduced into the aqueous phase below the 24-hour-old BSA film, the surface viscosity showed an increase (after a further 24 h) to a value around twice that for the original protein film. Hence, in this case, the new protein-polysaccharide interactions induced at the oil-water interface were sufficiently strong to influence considerably the viscoelastic properties of the adsorbed biopolymer layer. 

Hascall, V. C., Sajdera, S. W. Protein-polysaccharide complex from bovine nasal cartilage. The function of glycoprotein in the formation of aggregates. J. Biol. Chem. 244, 2384 (1969)... 

Polymer catalysts showing interactions with the substrate, similar to enzymes, were prepared and their catalytic activities on hydrolysis of polysaccharides were investigated. Kinetical analyses showed that hydrogen bonding and electrostatic interactions played important roles for enhancement of the reactions and that the hydrolysis rates of polysaccharides followed the Michaelis-Menten type kinetics, whereas the hydrolysis of low-molecular-weight analogs proceeded according to second-order kinetics. From thermodynamic analyses, the process of the complex formation in the reaction was characterized by remarkable decreases in enthalpy and entropy. The maximum rate enhancement obtained in the present experiment was fivefold on the basis of the reaction in the presence of sulfuric acid. 

Nakanishi, I., Kimura, K., Kusui, S., and Yamazaki, E. (1974). Complex formation of gel-forming bacterial (l,3)-P-D-glucans (curdlan-type polysaccharides) with dyes in aqueous solution. Carbohydr. Res. 32 47-52. 

Fig. 9 a, b. Complex formation of polyelectrolytes with rigid polymer chains such as polysaccharides. (a) pH Dependence of the composition of the complex. (1) Theoretical values assuming stoichiometry (2) Experimental values (b) Schematic representation of a ladder-like complex structure of one part of SCS and two parts of GC SCS = Sulfated cellulose, GC = glycol chitosan... 

Some plant galactomannans are also known to interact with milk proteins,310 plant lectins,311 and protein antibodies.312 It is not yet known whether these polysaccharides can exist in the form of complexes with seed proteins. Such complex-formation often results in increased stability of proteins towards heat inactivation, proteolytic degradation, and other unfavorable conditions. 

The formation of complexes affects both particle-solvent and particle-particle interactions. The solubility of proteins may be increased by their electrostatic complexing with anionic polysaccharides. Formation of titration-complexes may increase protein solubility and inhibit protein precipitation at the lEP. Anionic polysaccharides can act as protective hydrocoUoids inhibiting aggregation and precipitation of like-charged dispersed protein particles, for example, of denatured proteins. This protective action also can increase the stability of protein suspensions and oil-in-water emulsions stabilized by soluble protein-anionic polysaccharide complexes. 

When proteins and polysaccharides carry an opposite charge, complex formation is driven by the attractive electrostatic interactions between the two biopolymers. Soluble and insoluble complexes may be formed depending on the strength of the interactions, the balance of negative... 

The nature of complex-formation between cations and monosaccharides is now well understood this knowledge should form a firm basis for the study of cation-polysaccharide interactions. 

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