Binding, interchain

In polyelectrolyte solutions, the counterion condensation on linear polyelectrolyte chains is known to occur when the charge density along the chain exceeds the critical value [40]. Our work indicates the existence of a critical value for the separation distance between chains, where the interchain interaction changes drastically, most likely due to the transition in the binding mode of the counterions (see Fig. 13). Many peculiar forms of behavior, which are often interpreted by the cluster formation or the interchain organization of polyelectrolytes, have been reported for high concentrations of aqueous polyelectrolytes... 

FIG. 13 Schematic drawing of possible binding modes of counterions to polyelectrolyte chains. Counterions loosely bind and form a cloud around the polyelectrolyte chains when the interchain distance (d) is greater than 2.4 0.5 nm, while they strongly bind to form nearly neutral polyelectrolytes at smaller distances d < 2.4 0.5 nm). 

Figure 20.11 Papain digestion of IgG antibodies primarily results in cleavage in the hinge region above the interchain disulfides. This produces two heavy-light chain pairs, called Fab fragments, each containing one antigen binding site. The Fc region normally can be recovered intact.

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. 

From Ravanat s and Kohn s data, the transition observed for calcium activity is in the range of DP 10 to 20, which means that at least 5 to 10 Ca2+ cations are necessary to form a cooperative strong interchain binding. Until now, formation of chain dimers (as predicted in the egg-box ... 

A. General description Eptifibatide is a cyclic heptapeptide containing six amino acids and one mercaptopropionyl residue. An interchain disulfide bridge is formed between the cysteine amide and the mercaptopropionyl moieties. Eptifibatide binds to the platelet receptor glycoprotein (gp) Ilb/IIIa of human platelets and inhibits platelet aggregation. The eptifibatide peptide is produced by solution-phase peptide synthesis, and is purified by preparative reverse-phase liquid chromatography and lyophifized. 

The Ksv values for these ions are similar to those for Cu2+ and it may be anticipated that binding to the polymer by all three ions occurs with comparable strength due to reasonably similar Coulombic interactions between the divalent ions and the polymer. Since the polymer fluorescence is known to be strongly attenuated when interchain or intermolecular interactions occur, it may be that all or part of the quenching observed for these ions may be attributed to aggregation effects induced by association of the divalent cations with the polymer. 

Members of the trefoil factor family of small proteins are solid candidates to be mucin interchain cross-linkers (Otto and Thim 2005). For example, TFF1 is mainly expressed in the goblet cells of gastric mucosa, where it co-localizes with and binds to MUC5AC (Ruchaud-Sparagano et al. 2004). Yeast two-hybrid... 

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