Interchain hydrophobic bonds

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

It is proposed in this paper that the molecular flexibility, or in the case of cellulose, the lack thereof, is one of the fundamental factors that determines the suitability of a polymer for use as a fiber. Another factor is the set of interactions between molecules in the crystalline material. Those interactions, which depend on the accessible molecular shapes, diminish solubility, especially if both hydrogen and hydrophobic bonds are formed, as in the case for the common conformation of cellulose. The relatively limited range of shapes (a definition of stiffness) not only keeps the cellulose chains in a conformation that retains the interchain attractions but also minimizes increases in entropy in solution. 

Most proteins contain more than one polypeptide chain. The manner in which these chains associate determines quaternary structure. Binding involves the same types of noncovalent forces mentioned for tertiary structure van der Waals forces, hydrophobic and hydrophilic attractions, and hydrogen bonding. However, the interactions are now interchain rather than infrachain (tertiary structure determination). The quaternary structure of hemoglobin (four almost identical subunits) will be discussed in Chapter 4, that of superoxide dismutase (two identical subunits) will be discussed in Chapter 5, and that of nitrogenase (multiple dissimilar subunits) will be discussed in Chapter 6. 

Factors which influence properties chain length, branching vs. linear, nature of the monomer, density, interchain bonds, hydrophobic and hydrophilic interactions. 

The preparation and characterization of short peptidic molecules that adopt a stable and predictible structure in solution is a prerequisite for the construction of de now-designed artificial enzymes and proteins. In natural polypeptides, the secondary structures are parts of a larger system and their conformational stability is due to several intra- and interchain non-covalent interactions such as van der Waals forces, electrostatic forces, hydrogen bonding, and hydrophobic forces [2], However, these interactions are less important in short... 

Theoretical and experimental studies on the PP II structure showed that in an aqueous environment, water molecules form carbonyl-water-carbonyl H-bonds within the chain [117-119], which seems to be the driving force for favoring the trans conformation. Interchain water bridges in PP II are not possible because carbonyls in the PP II helix are sterically quite crowded by the neighboring atoms [120], The carbonyl-water-carbonyl clusters cannot be formed when the peptide adopts the PP I conformation. This explains why the PP I structure can be formed in hydrophobic solvents where this effect is negated. The PP I conformation has not yet been found in protein structures. 

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