Protein aqueous systems

Its solubility characteristics in aqueous systems are such that retention of toxicity to insects by dissolved crystal protein is always suspect, and loss of activity on dissolution owing to denaturation is often observed. The protein is soluble only in relatively strong aqueous alkali. Thus, it has been variously reported to be soluble in 0.01N- to 0.05N sodium hydroxide (1) and alkali at pH 10.5 in the presence of thioglycollate (35) we have also observed its solubility in alkali at pH 9.5 in the presence of urea and potassium boro hydride. One difference between the characteristic proteins produced by various strains of crystalliferous bacilli is observed in the degree of alka-... 

We have examined a number of different salts and have shown that the transition temperature can almost be altered at will (12), in many cases in line with the Hofmeister or lyotropic series (13-15J, a relationship found for many other aqueous systems such as hydrocarbon solubility and protein stability. 

Such carbonyls may be further oxidized using potassium permanganate (KMnO and perchloric acid (HCIO4) to convert all of these groups into carboxylic acids. Once functionalized in this manner, the nanotubes can be fully dispersed in aqueous systems. Kordas et al. (2006) used these derivatives to print nanotube patterns on paper or polymer surfaces to create conductive patterns for potential use in electronic circuitry. The carboxylates also may be used as conjugation sites to link other ligands or proteins to the nanotube surface using a carbodiimide reaction as previously discussed (Section 1, this chapter Chapter 2, Section 1.11 Chapter 3, Section 1). 

Carbodiimides are, in general, useful compounds for effecting certain dehydrative condensations, e.g., in the formation of amides, esters, and anhydrides. These two crystalline water-soluble carbodiimides are especially useful in the synthesis of peptides and in the modification of proteins. The excess of reagent and the co-product (the corresponding urea) are easily separated from products with limited solubility in water. The hydrochloride is best employed in nonaqueous solvents (methylene chloride, acetonitrile, dimethylformamide). The methiodide is relatively stable in neutral aqueous systems, and thus is recommended for those media. 

Water in oil microemulsions with reverse micelles provide an interesting alternative to normal organic solvents in enzyme catalysis with hydrophobic substrates. Reverse micelles are useful microreactors because they can host proteins like enzymes. Catalytic reactions with water insoluble substrates can occur at the large internal water-oil interface inside the microemulsion. The activity and stability of biomolecules can be controlled, mainly by the concentration of water in these media. With the exact knowledge of the phase behaviom" and the corresponding activity of enzymes the application of these media can lead to favomable effects compared to aqueous systems, like hyperactivity or increased stability of the enzymes. 

Tolstoguzov, V.B. (2000) Compositions and phase diagrams for aqueous systems based on proteins and polysaccharides. International Review of Cytology, 192, 3-31. 

The most popular method for measuring the polarity of a solute entails determination of the distribution constant between water and a water-immiscible solvent, e.g., octanol. However, because there is difficulty in dissolving proteins in the solvent, a two-phase aqueous system was developed (Shanbhag and Axelson, 1975). Albertson (1986) reported the construction of various aqueous phase systems for partitioning proteins, other macromolecules, and even cells. Recently, simpler aqueous biphase systems were selected for hydrophobic partitioning of proteins (Hachem et al., 1996). However, because of restrictions similar to those for HIC, as discussed above, it may be premature to replace the method used in Basic Protocol 5. The definition of hydrophobicity is based on the polarity of chemical compounds, which is closely related to the distribution between solvents of different polarities. This theory is similar to the elution mechanism of phase distribution chromatography as well as phase partition. However, complexity in the partition system and procedure hampers the broad use of the phase partition approaches. 

Shanbhag, V.P. and Axelsson, C.-G. 1975. Hydro-phobic interaction determined by partition in aqueous two-phase systems. Partition of proteins in systems containing fatty acid esters of polyethylene glycol). Eur. J. Biochem. 60 17-22. 

The properties of protein in aqueous systems depend on179) ... 

As with normal hydrocarbon-based surfactants, polymeric micelles have a core-shell structure in aqueous systems (Jones and Leroux, 1999). The shell is responsible for micelle stabilization and interactions with plasma proteins and cell membranes. It usually consists of chains of hydrophilic nonbiodegradable, biocompatible polymers such as PEO. The biodistribution of the carrier is mainly dictated by the nature of the hydrophilic shell (Yokoyama, 1998). PEO forms a dense brush around the micelle core preventing interaction between the micelle and proteins, for example, opsonins, which promote rapid circulatory clearance by the mononuclear phagocyte system (MPS) (Papisov, 1995). Other polymers such as pdty(sopropylacrylamide) (PNIPA) (Cammas etal., 1997 Chung etal., 1999) and poly(alkylacrylicacid) (Chen etal., 1995 Kwon and Kataoka, 1995 Kohorietal., 1998) can impart additional temperature or pH-sensitivity to the micelles, and may eventually be used to confer bioadhesive properties (Inoue et al., 1998). 

Proteins are dynamic molecules with respect to structure. The preferred folded structure for a given set of environmental conditions is that which has the minimum free energy. The driving force to assume a given folded structure is a thermodynamic force. In aqueous systems, the hydrophobic side-chains will endeavour to orient away from the surrounding water and towards the core of the molecule. However, for high surface activity, it is essential that the protein molecule should unfold and orient its hydrophobic side-chains towards the oil phase. A lack of hydrophilic residues usually does not restrict protein functionality at interfaces. Thus, flexible proteins can create a highly hydrated, mobile layer to stabilize an emulsion particle. 

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