Water, denatured protein studies

Ohtsuru et al. (25) have recently investigated the behavior of phosphatidylcholine in a model system that simulated soy milk. They used spin-labelled phosphatidylcholine (PC ) synthesized from egg lysolecithin and 12-nitroxide stearic acid anhydride. The ESR spectrum of a mixture of PC (250 yg) and native soy protein (20 mg) homogenized in water by sonication resembled that observed for PC alone before sonication. However, when PC (250 yg) was sonicated in the presence of heat-denatured soy protein (20 mg), splitting of the ESR signal occurred. On this basis, they postulated the existence of two phases PC making up a fluid lamella phase and PC immobilized probably due to the hydrophobic interaction with the denatured protein. In a study of a soy-milk model, Ohtsuru et al. (25) reported that a ternary protein-oil-PC complex occurred when the three materials were subjected to sonication under the proper condition. Based on data from the ESR study, a schematic model has been proposed for the reversible formation-deformation of the ternary complex in soy milk (Figure 2). 

The studies also revealed some factors that affect the stability of a protein at the electrode/electrolyte interface. On an electrode surface, the native conformation of a protein may be retained or distorted, depending on the extent of the interactions between them. Because in most of the water-soluble proteins the hydrophilic side chains are usually located on the exterior, irreversible adsorption and denaturation of proteins are expected to be considerably less on a hydrophilic electrode surface at which intervening water molecules are more tenaciously bound. Therefore, adsorption at both modified gold and edge-... 

Other Proteins. Since Reay and Dyer discovered that denaturation of myofibrillar proteins is of such profound importance, little attention has been given to the water-soluble proteins including enzymes and other proteins in the sarcoplasm, subcellular organelles, and cell membranes. Recently reports have appeared on the freeze denaturation of enzymes. These studies involved enzymes such as catalase, ADH, GDH, LDH, and MDH from sources other than fish (88,89,90) and attention was given to the effectiveness of various cryoprotective substances (89, 90). Comparable studies with enzymes from fish muscle are few in number (91). Studies on fish muscle proteins must be extended to this area if a complete picture of the freeze denaturation of fish muscle is to be obtained. It should be noted that freeze stable enzymes might have important effects during frozen storage of fish (92,93). 

The amide I band has been examined by Elliott et al. (1950) in native and denatured insulin, by Elliott et al. (1957) in lysozyme, and by Ambrose et al. (1951) in water-soluble silk. The band at 3200 cm" has also been investigated. Beer et al. (1959) have given a comprehensive list of proteins studied up to 1959, along with characteristic absorption bands. Bamford et al. (1956) have reviewed work done up to 1956 in the region between 5000 and 4500 cm (combination band of the N—H stretching frequency and that of the amide I or amide II band). The infrared dichroic properties of crystals of hemoglobin and ribonuclease have been observed in this region (Elliott and Ambrose, 1951 Elliott, 1952). 

The effects of divalent cations on bovine serum globulin in terms of salting-out and stabilization of the native form and salting-in and denaturation was studied by Arakawa and Timasheff (1984) in terms of the protein preferential hydration. This increased in the order Mn + Ni + < Ca + Ba + < Mg + < Na+ leading to increased salting-out and stability of the protein against denaturation. The binding of the divalent salts to the protein overcomes the ion exclusion from the surface due to competition for water of hydration. 

Wei and Srivastava [8] reported diffusion of polymers to be several orders of magnitude faster than through the zeolite chaimels (of comparable size) and also report the translocation time through the nanotube scales as N, where N is the number of monomers in a polymer. Gao et al. [9] calculated that a single-stranded DNA will spontaneously insert into the nanotubes from water solutions provided that the nanotube is big enough, attributing the mechanism to van der Waals attraction. Ye H and Hummer studied electrophoretic transport of nucleic acids through 1.5-nm carbon nanotubes. Their simulation showed that without electric field, RNA would remain trapped in the hydrophobic pores. Sorin and Pande [10] recently also demonstrated that confinement inside a nanotube denatures protein helices. 

The adsorption of proteins from solution onto polymeric surfaces depends on protein water, protein surface and surface-water interactions [51,52]. Our optical adsorption study indicates that hydrophobic surfaces preferentially adsorb denatured proteins from a mixed solution. This finding underhnes the amphiphilic nature of proteins and the important role of... 

Gels of denatured egg albumin in mixtures of water and n-propyl alcohol were studied by Jirgensons (1936). The alcohol served both as denaturing agent and as a solvent to prevent the denatured protein from... 

Many reports and review articles " have appeared on the interaction between proteins and surfactants, ever since surfactants were found to be strong denaturants of water-soluble proteins. Much information on proteins is still derived from studies of their interaction with amphiphiles. 

Depending upon the kind of information desired, membrane bilayer samples can be prepared either oriented with respect to the applied field, or as random dispersions. For most studies, full hydration (>30 wt% of water) is desired, especially for protein studies where denaturation may occur and biological function be lost without sufficient amounts of water present. 

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