Proteins with globular protein

Note Globular-chain crystals usually occur with globular proteins. 

Figure 16.13 The free energy of denaturation AfjG as a function of temperature for a number of proteins Lys = lysozyme Rna = ribonuclease A Ct = a-chymotrypsin Cyt = cytochrome c Mb = metmyoglobin Tr = Trypsin and PTI2 = the dimer of pancreatic trypsin inhibitor. Reprinted with permission from P. L. Privalov, Stability of Proteins — Small Globular Proteins, Adv. Prot. Chem., 33, 167 (1979).

Figure 6.3 Ultrafiltration membranes are rated on the basis of nominal molecular weight cut-off, but the shape of the molecule to be retained has a major effect on retentivity. Linear molecules pass through a membrane, whereas globular molecules of the same molecular weight may be retained. The table shows typical results obtained with globular protein molecules and linear polydextran for the same polysulfone membrane [8]...

Figure 1-8. Membrane model with globular proteins interspersed within a lipid bilayer. The ionic head of phospholipids is represented by -O, and the fatty acid side chains leading to thenonpolar tail are indicated by the two wavy lines.

The cell membrane is associated with intrinsic and extrinsic proteins. Intrinsic proteins are globular proteins that generally span the bilayer and are held within the membrane by hydrophobic and electrostatic interactions. The proteins can form channels, carriers, or pumps that enable polar molecules to cross the membrane. 

Petit F., Audebert R., Iliopoulos I. Interactions of hydrophobic ally modified polyfsodium acrylate) with globular proteins. Colloid Polym. Sci. 1995 273 777-781. 

One source of information, hydrodynamic measurements, has recently been reviewed by Squire and Himmel ( ) Their analysis suggests large amounts of water associated with globular proteins, but even their restricted data set shows large variations between the amount of hydration calculated from sedimentation or diffusion results. Because the cube of the friction factor enters into the... 

Polypeptides and proteins can undergo other conformational changes, especially when they exist in relatively compact structures wherein the backbone can fold back on itself, or make a turn (i.e., a site where the polypeptide chain reverses its overall direction). It is these reverse turns (e.g., p-turn or hairpin bend) that afford proteins with globular properties (18). A further discussion of turns is beyond the scope of this chapter, but the interested reader can find many good discussions ofthis topic in other sources (16,19). 

Consider a situation with globular protein subunits that are soluble in solution at a sufficiently low temperature and that have simple complementary hydrophobic surfaces covered with much hydrophobic hydration, as in Figure 8.2A. Raising the temperature from below to... 

Lipids, lipoproteins, and proteins makeup cytoplasmic membranes. This membrane is a diffusion barrier for ions, nutrients, transport systems, and most importantly, water. It is composed of a lipid grouping with globular proteins that penetrate the lipid bilayer. Most antibacterial agents that inhibit cytoplasmic membranes do so by influencing the balance of cations, anions, or neutral compounds, thus disrupting membrane operation. Of interest is that fungal... 

In a simple case the diffusion coefficients of spheres can be determined via the Stokes-Einstein relationship see Section 12.6.4. While such a relationship was originally derived with hard spheres in mind, it can also be used with globular proteins such as bovine serum albumin (59). Dynamic light-scattering can be used to study aggregation, adsorption, and structural changes as well as chain dynamics. 

A wide variety of synthetic and natural PE can interact with globular proteins to form stable protein-polyelectrolyte complexes (PE-P) that result in the formation of soluble or non-soluble complexes [5, 47]. The non-soluble complex can be easily separated by centrifugation or simple decantation. Precipitation as a concentration step offers several advantages in that it is easy to scale up, uses simple equipment and can be based on a large variety of alternative precipitants. When PE-P is specifically formed with one of the proteins in the crude extract followed by a phase separation, the process could be used as a convenient strategy for the isolation and purification of the target protein [8]. 

Hydrogen bonding stabilizes some protein molecules in helical forms, and disulfide cross-links stabilize some protein molecules in globular forms. We shall consider helical structures in Sec. 1.11 and shall learn more about ellipsoidal globular proteins in the chapters concerned with the solution properties of polymers, especially Chap. 9. Both secondary and tertiary levels of structure are also influenced by the distribution of polar and nonpolar amino acid molecules relative to the aqueous environment of the protein molecules. Nonpolar amino acids are designated in Table 1.3. 

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