Surface salt bridges

Strop P, Mayo SL (2000) Contribution of surface salt bridges to protein stability. Biochemistry 39(6) 1251—1255... 

Luisi DL et al (2003) Surface salt bridges, double-mutant cycles, and protein stability an experimental and computational analysis of the interaction of the Asp 23 side chain with the N-terminus of the N-terminal domain of the ribosomal protein 19. Biochemistry... 

A. Horovitz, L. Serrano, B. Avron, M. Bycroft, and A. R. Fersht,/. Mol. Biol., 216, 1031 (1990). Strength and Cooperativity of Contributions of Surface Salt Bridges to Protein Stability. 

Strop, P., and Mayo, S. L. "Contribution of Surface Salt Bridges to Protein Stability." Biochemistry 39,1251-1255 (2000). 

The evolution of nitrogen aids in removing dissolved air. A salt bridge (4 mm tube) attached to the saturated calomel electrode is filled with 3 per cent agar gel saturated with potassium chloride and its tip is placed within 1 mm of the mercury cathode when the mercury is not being stirred this ensures that the tip trails in the mercury surface when the latter is stirred. It is essential that the mercury-solution interface (not merely the solution) be vigorously stirred, and for this purpose the propeller blades of the glass stirrer are partially immersed in the mercury. 

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... 

Thus, the Volta potential may be operationally defined as the compensating voltage of the cell of Scheme 16. However, it should be stressed that the compensating voltage of a voltaic cell is not always the direct measure of the Volta potential. The appropriate mutual arrangement of phases, as well as application of reversible electrodes or salt bridges in the systems, allows measurement of not only the Volta potential but also the surface and the Galvani potentials. These possibilities are schematically illustrated by [15]... 

There is no salt bridge or any other means of stopping current flow in the microscopic circuit on the iron surface, so electrochemical reduction occurs at the right-hand side of the cell, and oxidation occurs at the left ... 

The polar, charged residues Asp, Glu, Lys, Arg and, in its protonated form, His, will often be found at the surface of proteins, where they may not only interact with the polar layers of ordered water molecules surrounding the protein, but may also participate in hydrogen bonds and salt bridges with other polar charged residues. 

Electroanalytical techniques are an extension of classical oxidation-reduction chemistry, and indeed oxidation and reduction processes occur at the surface of or within the two electrodes, oxidation at one and reduction at the other. Electrons are consumed by the reduction process at one electrode and generated by the oxidation process at the other. The electrode at which oxidation occurs is termed the anode. The electrode at which reduction occurs is termed the cathode. The complete system, with the anode connected to the cathode via an external conductor, is often called a cell. The individual oxidation and reduction reactions are called half-reactions. The individual electrodes with their half-reactions are called half-cells. As we shall see in this chapter, the half-cells are often in separate containers (mostly to prevent contamination) and are themselves often referred to as electrodes because they are housed in portable glass or plastic tubes. In any case, there must be contact between the half-cells to facilitate ionic diffusion. This contact is called the salt bridge and may take the form of an inverted U-shaped tube filled with an electrolyte solution, as shown in Figure 14.2, or, in most cases, a small fibrous plug at the tip of the portable unit, as we will see later in this chapter. 

The titration-cell Figure 17.2 (a) essentially comprises of apyrex 100-ml, four-necked, flat-bottomed flask. A semimicro burette (B) (graduated in 0.01 ml), a 2-way gas-inlet tube (A) to enable N2 to pass either through the solution or simply over its surface, a dropping mercury electrode (C) and an agar-potassium salt-bridge are duly fitted into the four necks with the help of air-tight rubber stoppers. 

---