Association, chain

Polypropylene chains associate with one another because of attractive van der Waals forces The extent of this association is relatively large for isotactic and... 

The constant domain has a stable framework structure composed of two antiparallel sheets comprising seven p strands, four in one sheet and three in the other. The variable domains have a similar framework structure but comprising nine p strands, five in one sheet and four in the other. The three hypervariable regions are in loops at one end of the variable domain. The variable domains from the heavy and light chains associate through their five-stranded p sheets to form a barrel with the hypervariable loop regions from both domains close together at the top of the barrel. 

Myosin-I molecules have several IQ sequences on or near the head and have light chains associated with them (Cheney and Mooseker, 1992 Cheney et al., 1993). Frequently, the light chains appear to be calmodulin molecules and some myosin-I molecules can bind three to four molecules of calmodulin at one time. Brush-border and adrenal myosin-I also bind calmodulin. Acanthamoeba myosin-I has a light chain that can be removed, in vitro, without adversely affecting the ATPase activity or the heavy chain phosphorylation (Korn and Hammer, 1988). The role of these calmodulin molecules in regulating myosin-I is complex and poorly understood. One possibility is that the calmodulin molecules dissociate from the heavy chains when calcium binds to the calmodulin, thereby imparting greater flexibility to the head of the myosin-I molecules. 

In contrast, observation of the c.d. with the addition of Ca(OH)2, as a function of d.p., demonstrated that terminal and central units react differently towards Ca ". This is illustrated in Fig. 27 for the dimer and the polymer. Again, the intensity of the c.d. band decreases as the polymer binds calcium and begins to gel. Results for both salt forms are attributed to a helix having a two-fold screw-symmetry, in analogy with calcium pectates. The gelling would then involve a multi-chain association, with crosslinking by the calcium ions to form an egg box structure. ... 

For the sake of clarity, the resonances belonging to the individual groups have been isolated from the data and presented in tables III and IV. Table III shows the resonances associated with the side chain (carbons 16-19). Examination of the data reveals that each side chain presents a unique set of resonances (Table III). For example, resonances at 6 166.5, 136.8, 126.5 and 18.3 uniquely describe the side chain associated with elegin (XII), repdiolide (XIV) and epoxyrepdiolide (VII), i.e., a side chain ester with a double bond between C-17 and C-18. Likewise for each of the other three side chains one can completely describe them on the basis of their 33c-NMR spectra alone. 

Figure 2 compares the conformational transition curves of wild-type yeast glucan (branch frequency = 0.20) and PGG (branch frequency = 0.50). Wild-type yeast glucan required approximately 0.1M NaOH to disrupt the triple helical conformation, whereas this transition is observed at approximately 0.04 M NaOH with PGG. This trend is consistent with the observation that curdlan, an entirely linear p-D(l-3)-linked glucan, requires approximately 0.25M NaOH to disrupt the ordered conformation (76). Hence, it is concluded that the highly branched PGG molecules only form weak inter-chain associations resulting in the formation of predominantly single-helical zones. 

The principles of collagen folding differ markedly from other known proteins since single monomers cannot fold. Triple helix folding is a multi-step process involving chain association, registration, nucleation and... 

When carrageenans form gels the chains associate through double helices. Any p- or p-carrageenan present inhibits this process. 

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. 

Free energy variations with temperature can also be used to estimate reaction enthalpies. However, few studies devoted to the temperature dependence of adsorption phenomena have been published. In one such study of potassium octyl hydroxamate adsorption on barite, calcite and bastnaesite, it was observed that adsorption increased markedly with temperature, which suggested the enthalpies were endothermic (26). The resulting large positive entropies were attributed to loosening of ordered water structure, both at the mineral surface and in the solvent surrounding octyl hydroxamate ions during the adsorption process, as well as hydrophobic chain association effects. 

Other proteins also participate in the integration process. One class is composed of molecular chaperones such as SecA in bacteria and Hsp70 or BiP in eukaryotes (Qi and Bernstein, 1999 Schekman, 1994 Mothes et al., 1997 Hamman et al., 1998 Pilon and Schekman, 1999). Another important player in the eukaryotic system is TRAM (translocating chain-associating membrane protein) (Walter, 1992). 

Figure 12. Four state model of the hydration-mediated counterion—side chain association—dissociation equilibrium, of Mauritz. (Reprinted with permission from ref 107. Copyright 1982 American Chemical Society.)...

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