The Effects of Salts on the Activity and 

 Solubility of Haemoglobin 



G. S. ADAIR 



Mixtures of haemoglobin and phosphate buffers have special 

 properties that make it possible to evaluate the solubility and the 

 activity of the protein at the same pH value and salt content. 



Functions termed excess coefficients can be computed from 

 measurements of the distribution of phosphates across collodion 

 membranes, using highly soluble species of haemoglobin and super 

 saturated solutions of horse haemoglobin. 



Methods and formulae for calculating the activity of haemoglobin 

 from measurements of excess coefficients are described. 



It is shown that salts cause relatively large changes in the activity 

 of haemoglobin in solution, and that there must be relatively large 

 changes in the activity of the protein in the solid phase. 



The composition of crystals of haemoglobin is influenced by the 

 medium in which they are suspended, and it has been suggested that 

 changes in the composition of the crystals are important for the 

 interpretation of measurements of solubility of proteins in terms of 

 activity coefficients. 1 E. J. Cohn and J. T. Edsall 2 on the other hand 

 have suggested that the activity of the protein component in the crystal 

 is approximately constant. They have shown that the effects of salts 

 on the solubilities of amino acids and of proteins are similar, and it is 

 known that the activity is constant in all saturated solutions of a pure 

 substance. They also refer to electrometric measurements made with 

 metallic or amalgam electrodes 3 in support of the hypothesis that the 

 activity of the protein component is a constant. 



Direct electrometric methods are not available for the buffer 

 mixtures usually employed for studying the solubilities of proteins. 

 Phosphate buffers have been used for extensive series of measurements 

 of the solubility of haemoglobin. In the present communication an 

 independent method is developed for calculating the activity of 

 haemoglobin in phosphate buffers from measurements of membrane 

 equilibrium. 



The addition of a protein to a dilute solution of an inorganic salt 

 usually tends to diminish the activity of the salt. If only one salt be 

 present, at a constant molality, variations in the activity of the salt can 

 be correlated with variations in the activity of the protein by a formula 

 due to N. Bjerrum 4 . 



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