Studies on Human Adult and Foetal Haemoglobins 



In Figure 10 curve 1 the solubility of HbCO is plotted against ionic 

 strength of potassium phosphate buffer at pH 6-7 and 0°C. The data 

 are represented by Cohn's equation (log S = /? — K[ r / 2 ) for ionic 

 strengths T / 2 = 4 to 6. The curves for HbO a , MetHb and Hb (curves 

 2-4) have been plotted for comparison. Curve 4 (Hb) was obtained 

 by dissolving up crystals in buffer, curves 1-3 by salting out crystals 

 with strong phosphate buffer. These show that Hb is very much less 

 soluble than the other three haemoglobin derivatives HbCO, Hb0 2 or 

 MetHb, whose solubilities lie fairly close together. 



Figure 10 shows also that higher solubility values are obtained by 

 approaching the equilibrium from the undersaturated side, i.e. by 

 dissolving up crystals in buffer (HbCO curve 5), than by approaching 

 the equilibrium from the supersaturated side, i.e. by salting out crystals 

 by addition of strong buffer (HbCO, curve 1). The difference between 

 curve 5 and curve 1 is considerable, and the true equilibrium value 

 will probably be somewhere between them. The difference does not 

 seem to be due to insufficient time being given for the true equilibrium 

 to be reached as values remained constant for as long as a week after 

 the completion of the experiment. There seems, moreover, to be a 

 tendency to overshoot the equilibrium, higher values being obtained 

 by approaching from below than by approaching from above. This 

 is remarkable. 



There is a difference also in the equilibrium values for amorphous 

 and for crystalline material, and this may be in some way concerned 

 with the above observation. Amorphous HbCO was dissolved in 

 phosphate buffer to give a solution in equilibrium with amorphous 

 solid phase. On standing the amorphous HbCO crystallized and the 

 amount in solution decreased, the amorphous material being con- 

 siderably more soluble than the crystalline. 



The variation with pH of solubility of HbCO in potassium phosphate 

 buffer T / 2 = 4-6 at 0°C appears to be slight between pH 6-5 and/?H 7-1 

 (Figure 11). 



JOr 



Figure 1 1 . Variation with pH of human adult u l0 

 HbCO solubility. - 



The solubility of the haemoglobin derivatives, adult HbCO, Hb0 2 , 

 MetHb and foetal HbCO and Hb, in 2M potassium phosphate buffer 

 pH 6-7 at different temperatures is plotted in Figure 12 (curves 1-6) 

 against temperature. Hb, both adult and foetal (curves 4 and 6) has 



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H— 18 



