Arda Alden Green 



217 



Hemoglobin is a globulin. Its solubility is increased upon the addition of 

 low concentrations of salt^ and it is "salted out" at higher concentrations of 

 salt. Figure 1 represents the solubility of crystalline horse carboxyhemoglobin' 

 at constant pH and temperature in concentrated solutions of various electro- 

 lytes. 



The slopes of the lines, and therefore the K/ values vary with the kind of 

 salt used. For this protein K/ decreases in the order, KH,PO^ + K2HPO , 

 Na,SO„ Na^CgH-O,, (NH,),SO„ and MgSO,. This is essentially the same 



A.OJU ZD 3.Q JU. 4.0 



Fig. 2. The solubility of hemoglobin in concentrated phosphate buffers. 



of varying temperature and pH. 



(From Green, A. A.: Jl. Biol. Chem. 93:507, 1931.) 



order as the series given by Hofmeister' in 1888. As is to be expected, the 

 values of K/ vary from one protein to another in the same salt. 



b. Effect of Temperature o?i Solubility 



K/ is, however, independent of temperature and pH. That is, curves for the 

 logarithm of the solubility in the same salt are parallel to each other at 

 various pH values as are also curves at various temperatures. This is apparent 

 in figure 2." 



Hemoglobin is more soluble at 0° than at 25° C. at high salt concentrations, 

 which is the reverse of the effect of temperature on solubility in low concentra- 

 tions of salt. This phenomenon is also exhibited by other proteins, including 

 the least soluble of the pseudoglobulins from serum. The data of S0rensen and 

 H0yrup" on the solubility of egg albumin in ammonium sulfate solutions at 

 various temperatures again show K/ to be independent of temperature, and 

 again the solubility is greater at 0° C. than at 20° C, but increases at higher 

 temperature. 



Thus, for a given protein, variation in K/ describes the effect of the type 



