A Solubility Study of Foetal and Adult Sheep Haemoglobin 



further increase of the haemoglobin concentration in the solution 

 could be observed. Then the dissolved protein and the precipitate 

 were separated, and the concentration of CO-Hb in the solution was 

 measured colorimetrically. 



A portion of the precipitate was examined using an ordinary 

 microscope. 



RESULTS 



The effect of pH on the solubility of the Hb of a foetus, 100 days old, 

 and on that of its mother was investigated. The equilibrium was 

 approached both from the undersaturated and the supersaturated side. 

 Figure 1 shows the results of the determinations. At pH 5-5 the 

 solubilities of the two proteins are the same, at more acid />H's the 

 foetal Hb is the more soluble, and at more alkaline pH's the adult 

 Hb is more soluble than the foetal Hb. The shapes of the foetal and 

 adult graph are widely different. At pH 7-2 the solubility of the 

 maternal Hb is more than 20 times higher than that of the foetal Hb. 

 The shape of the maternal graph is rather similar to the j^H-solubility 

 graph of adult horse Hb as published by S. P. L. Sorensen and M. 

 Sorensen 3 . This j?H-solubility graph is, however, by no means typical 

 of all adult mammals, e.g. the corresponding graph for adult human 

 Hb has a very different course. (Unpublished observations.) 



In ' variable solvent ' experiments, the logarithm of the solubility 

 of a pure protein is expected to be linearly related to the electrolyte 

 concentration. Several samples of adult Hb were studied using this 

 method, at two widely different pWs—pH 4-7 and 7-2. The solubility 

 of the different samples was not always identical, and neither was the 

 log solubility graph always strictly linear (Figure 2). Still, the graphs 

 approached linearity. The same was found to be true of the samples 

 obtained from foetuses younger than 120 days (Figure 3). However, 

 after the 120th day of the foetal life and during the first month of 

 post-natal life the solubility diagrams at varying electrolyte concen- 

 trations were largely irregular. 



Theoretically, a solubility graph of the ' variable solvent ' type can 

 be expected to deviate markedly from linearity, only if the components 

 of a mixture have considerably different additive solubilities. If the 

 solubilities of the components, however, overlap to a great extent, the 

 deviation from linearity is difficult to observe. Therefore, both adult 

 and foetal Hb were investigated also according to the ' constant 

 solvent ' technique. It turned out that the solubility diagrams thus 

 obtained in both cases were characteristic of a two-component system. 

 Figure 4 shows the solubility diagram of the Hb of a foetus, 114 days 

 old, at three different pWs. When the solubilities of the two com- 



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