Molal surface tension increment

Table I. Relative Effectiveness of Various Ions in Stabiliiinq the Native" Form of Collaqen and Ribonuclease <61 and the Predicted Relative Order Using the Molal Surface Tension Increment (7)...

The combination of the hydrophobic salting out and the electrostatic salting in terms explains very nicely the Class I type behavior. The data for carboxyhemoglobin and fibrinogen are well fitted by the theory (Figure 10). Also the order of decreasing molal surface tension increment generally follows the lyotropic order (7). 

TABLE 6 Characteristic Molal Surface Tension Increments of Different Salts Used in HP-HIC... 

Salt Molal surface tension increment a X IO]dyne g cm" 1 mole - 1... 

It is shown 30) that the analysis of a relationship between the salting-out constants of a given protein and the molal surface tension increments makes it possible to estimate the relative surface hydrophobicity which is calculated as the ratio of the nonpolar surface area to the molecular weight of the protein. According to the concept developed by Melander et al 30), the hydrophobic character of a protein is believed to be constant at both high and physiological concentrations of different inorganic salts, which seems to be untrue in most cases (see below). 

The increase in retention at a given concentration depends on both the anion and the cation of the salt. Speciflcally, the retention increment depends on the molal surface tension increment of the salt. Table 13.1 contains this value for various salts. The higher the value, the greater is the retention at a pven concentration. It should be noted that the order in the table parallels the Hofmeister salting-out series (12). 

Thus, sodium citrate, on the basis of its molal surface tension increment and high solubility, would appear to be a good choice as an HIC kosmotropic salt. However, citrate salts are well known for their ability to bind selectively to many proteins at low concentrations, a feature that can be exploited [189-191] in the stabilization of multimeric NAD-dependent enzymes. 

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