Globular proteins interactions

Table 1 Techniques Used in the Study of Surfactant-Globular Protein Interaction...

The Stokes-Einstein equation has already been presented. It was noted that its vahdity was restricted to large solutes, such as spherical macromolecules and particles in a continuum solvent. The equation has also been found to predict accurately the diffusion coefficient of spherical latex particles and globular proteins. Corrections to Stokes-Einstein for molecules approximating spheroids is given by Tanford. Since solute-solute interactions are ignored in this theory, it applies in the dilute range only. 

No region of the cytochrome penetrates the membrane nevertheless, the cytochrome subunit is an integral part of this reaction center complex, held through protein-protein interactions similar to those in soluble globular multisubunit proteins. The protein-protein interactions that bind cytochrome in the reaction center of Rhodopseudomonas viridis are strong enough to survive the purification procedure. However, when the reaction center of Rhodohacter sphaeroides is isolated, the cytochrome is lost, even though the structures of the L, M, and H subunits are very similar in the two species. 

Protein 4.1, a globular protein, binds tightly to the tail end of spectrin, near the actin-binding site of the latter, and thus is part of a protein 4.1-spectrin-actin ternary complex. Protein 4.1 also binds to the integral proteins, glycophorins A and C, thereby attaching the ternary complex to the membrane. In addition, protein 4.1 may interact with certain membrane phospholipids, thus connecting the lipid bilayer to the cytoskeleton. 

The structure and structural stability of globular proteins in aqueous solution are the result of various interactions inside the protein molecule, between the protein and the water, and among the water molecules (Norde 2003a). The... 

The main contributions to AadsG for a globular protein are from electrostatic, dispersion, and hydrophobic forces and from changes in the structure of the protein molecule. Although in this section these contributions are discussed individually, strict separation of the influence of these forces on the overall adsorption process of a protein is not possible. For instance, adsorption-induced alteration of the protein structure affects the electrostatic and hydrophobic interaction between the protein and the surface. When the sorbent surface is not smooth but is covered with (polymeric)... 

The Hamaker constant for interaction across water is about 6.5x10 21J for globular proteins (Nir 1977) and 2-5xl0 2oJ for such oxides as silica and metal oxides (Lyklema 1991c). Based on these values and applying (6) and (4) to a spherical protein molecule having a radius of 3 nm at a distance of 0.1 nm from the surface of a soil particle, AadsGdisp at... 

In this chapter the roles of various physico-chemical parameters in the interaction between globular proteins, e.g. enzymes, and soil minerals have been discussed semi-quantitatively. Knowledge of the mechanism of that interaction provides a basis to manipulate biological activity in soils. 

Strand-turn-strand motifs in /1-solenoids differ fundamentally from those found in globular proteins. In globular structures, two adjacent strands with an intervening /l-turn form an antiparallel structure called a /1-hairpin (Fig. 10A). In /1-solenoids, the polypeptide chain also folds back on itself, but the flanking /1-strands make contact via their side chains rather than interacting via H-bonds of the backbone (Fig. 10A). As a result, consecutive strands find themselves in two different, parallel, /1-sheets. The latter strand-turn-strand structure is called a /1-arch, and its turn, a /1-arc (Hennetin et at., 2006 Yoder and Jurnak, 1995). In /1-solenoids, /1-arches stack in-register to form /1-arcades which have two parallel /1-sheets assembled from corresponding strands in successive layers. 

Figure 11.5 Globular proteins. The folding of a polypeptide chain in a globular form is stabilized by hydrophobic interactions and some covalent bonding, particularly the disulphide bond between cysteine residues. The polypeptide chain shows some sections which are regular and helical in nature and other sections, particularly at bends and folds, where the conformation of the chain is distorted.

Strambini and Galley have used tryptophan anisotropy to measure the rotation of proteins in glassy solvents as a function of temperature. They found that the anisotropy of tryptophan phosphorescence reflected the size of globular proteins in glycerol buffer in the temperature range -90 to -70°C.(84 85) Tryptophan phosphorescence of erythrocyte ghosts depolarized discontinuously as a function of temperature. These authors interpreted the complex temperature dependence to indicate protein-protein interactions in the membrane. 

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