Multiple salt bridges

Wilson (1974) emphasized the importance of wetting the substrate surface. Later, as the reaction proceeded, these hydrogen bonds would be replaced by ionic salt bridges. Wilson stressed the importance of the polymeric nature of these cements in adhesion. Their polymeric nature allowed interfacial gaps between cement and substrate to be bridged and also provided a multiplicity of bonds. Under oral conditions, where the substrate is subject to change, adhesive bonds will be broken, but if there are a multiplicity of these, attachment of the cement to the substrate will endure and allow broken bonds to be re-established. It is significant that... 

Figure 10.19 Binding of pseudosubstrate to protein kinase A. Notice that the inhibitor makes multiple contacts with the enzyme. The two arginine side chains of the pseudosubstrate form salt bridges with three glutamate carboxylate groups. Hydrophobic interactions are also important in the recognition of substrate. The isoleucine residue of the pseudosubstrate is in contact with a pair of leucine residues of the enzyme.

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