A Solubility Study of Foetal and Adult Sheep Haemoglobin 



basis of the solubility characteristics common to every series the 

 approximate composition of the transition samples was determined. 

 In Figure 5 the probable limits of the composition of each sample is 

 indicated with a vertical line. The change from 100 per cent foetal to 

 100 per cent adult type Hb is passed within two or three months. 



One lamb, whose Hb was followed from the age of 3 to 137 days, 

 was an exception to the rest of the animals. In this lamb the transition 

 could not be explained as a gradual intermixture of the foetal with 

 the adult Hb. The transition obviously led to the production of a 

 third type of Hb. At pH 4-7 both its solubility and the crystal habit 

 corresponded to the adult type of Hb, whereas at pH 7-2 the final Hb 

 had the properties of the foetal type of Hb. It apparently was not a 

 mixture of these two substances. Further studies on this lamb were 

 interrupted by its death, the cause of which remained undetermined. 



DISCUSSION 



The physico-chemical methods which have been used in the identifi- 

 cation and purification of proteins have different degrees of selectivity. 

 As to the homogeneity of a given sample of protein, only suitably 

 conducted solubility experiments can be expected to give an ultimate 

 answer. The electrophoresis and the ultracentrifuge can indicate the 

 presence of a mixture, but, on the other hand, they never can exclude 

 the possibility of its existence. The evidence of the present work 

 suggests, that both foetal and adult sheep Hb are composed of two 

 nearly related proteins. This finding, however, still requires to be 

 confirmed by the separation of the pure components. 



The equilibrium achieved between the dissolved protein and the 

 solution was different when it was approached from either the super- 

 saturated or from the undersaturated side. There obviously is in the 

 Hb solutions some factor, which tends to stabilize the supersaturated 

 state. The uneven electrolyte distribution between the crystal water 

 and the mother liquor can hardly be the sole cause of this super- 

 saturation. The finding, that the tendency to supersaturation was the 

 less the higher the proportion of the total Hb in the precipitate, suggests 

 that this supersaturation may be due to some ' protective colloid ' 

 which is precipitated with the Hb, but more rapidly than the Hb itself. 

 This question, however, requires further research. 



The mixtures of foetal and adult type Hb showed much higher 

 solubilities than the sum of the solubilities of the components. 

 This phenomenon of supersaturation occurred independently of the 

 direction, from which the equilibrium was approached. This increase 

 in the solubility can be understood as a manifestation of an increased 



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