Studies on Human Adult and Foetal Haemoglobins 



The more theoretical aspects of the relation of crystallinity to solu- 

 bility are discussed by G. S. Hartley 25 . 



The pH curve (Figure 11) is very flat between pH 6-5 and pH 7*1. 

 This flatness is possibly to be expected where the protein is able to 

 combine to such a large extent with ions, but it is difficult to be sure 

 that the ionic strengths of the buffers are exactly comparable for all 

 the /?H's studied. The simple theory of phosphate dissociation 26 is 

 probably not quite adequate for these very strong solutions. 



The solubility of adult HbCO, Hb0 2 and MetHb in strong salt 

 solution (2M phosphate) decreases at first with temperature, then 

 increases again. Adult Hb has no solubility-temperature coefficient 

 in this solvent but in dilute sodium chloride solution the solubility 

 increases rapidly with temperature. It is a property often observed 

 in proteins that in strong salt solutions the solubility decreases as the 

 temperature rises, while in salt free or in very dilute salt solution the 

 solubility increases as the temperature rises. A. A. Green 27 claims 

 to have crystallized human haemoglobin using this property. The 

 solubility-temperature curve has therefore a different shape according 

 to whether the solubility is measured in strong or in dilute salt solution. 

 There appears to be a discontinuity between these two measurements 

 for human adult HbCO which has no true solubility in phosphate 

 buffers of ionic strength less than about T / 2 — 4 (pH 6-7). Horse HbCO 

 has a true solubility 7 at r / 2 = 2. 



Human adult HbCO crystals contain 58-6 per cent HbCO, the 

 molecules are isodiametric and their arrangement in the lattice 

 approaches that of close packed spheres, each with its sheath of 

 bound water, the remaining 41.4 per cent being salt and water 28 . 

 This sets an upper limit to the solubility in salt solutions, and it is 

 difficult to see how Drabkin 9 could have obtained a 63 per cent Hb0 2 

 solution. A solution 40 per cent saturated with HbCO is extremely 

 viscous. 



CONCLUSIONS 



This work shows that in spite of the difficulties in obtaining solubility 

 data from such viscous solutions, the results can lead to some useful 

 classifications among haemoglobins and their derivatives. Human Hb 

 is distinct from HbCO, Hb0 2 and MetHb (both in the adult and in 

 the foetal series) in crystal form and solubility behaviour and the same 

 distinction is clear in these and many other properties between the 

 adult and the foetal haemoglobins themselves. 



We wish to thank the Bernhard Barron Memorial Laboratory, Queen 

 Charlotte's Hospital, London for co-operation in supplying foetal blood 

 and for some of the photographs, Dr. A. H.T. Robb-Smith, Department 



277 



