The effects of 22 lyotropic salts on the polymerization of deoxygenated sickle hemoglobin (deoxy-Hb S) were evaluated. The equilibrium solubility was measured as the saturation concentration, cBat, after phase separation by centrifugation at 30°C. The linear plots of csat uersus salt concentration allowed the assignment of particular cations or anions as either salting-in (csat increased) or salting-out (csat decreased) agents. Divalent cations were considerably more effective than univalent

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... ions as salting-in agents. Overall, the effects of cations on the solubility of deoxy-Hb S were: Ca2+ > MS' > NH4+ > Li+ > Cs+, Na+ > Rb', K'. Univalent anions in the presence of the counter cation Na+ were, with the exception of F-, salting-in agents which followed the order of the Hofmeister series (Hofmeister, F. (1888) Arch. Exp. Pathol. Pharmakd. 24, 247-260): SCN-> Clod-, I-> Br-> Cl-. Such differential effects were not observed, however, in the presence of the guanidinium cation. Instead, all four guanidinium salts evaluated were potent salting-in agents and increased csst to the same extent regardless of the counter anion (SCN-, Cl-, NOa-, S04'-). This uniformity of response most likely results from the extremely potent saltingin capacity of the guanidinium cation, which completely overwhelms any expression of the counter anion. Three anions (F-, HP04'-, and SOd2-) behaved overall as salting-out agents whose molar effectiveness was: SOJ2-> HPQd2-> F-. In general, the magnitude and the direction of the effect of salts on solubility depend on the specific ions involved. Moreover, cations and anions act in roughly additive fashion.