h. m. jope and J. r. p. o'brien 



greater tendency to split into smaller molecular units than has sheep 

 adult haemoglobin. H. Gutfreund 21 has examined this property in 

 human haemoglobins and reports that there is no difference between 

 human adult and foetal haemoglobins in their tendency to split on 

 dilution. He also reports that the molecular weight of human foetal 

 haemoglobin, deduced from osmotic pressure measurements, is the 

 same as that of the adult, 67,000. There is so far no satisfactory sedi- 

 mentation and diffusion constant study of human foetal haemoglobin, 

 but this is at present being carried out on the preparations described 

 here, by R. Cecil on the Oxford ultracentrifuge. 



X-ray data 11 show human adult HbCO, Hb0 2 and MetHb to be 

 orthorhombic and not tetragonal as stated by Drabkin 9 ' 10 , though 

 the difference in crystal measurements required by a tetragonal system 

 is only very slight. It is unfortunate that human HbCO crystals 

 did not give x-ray diffraction patterns which could yield further 

 information about the molecule. 



Human adult Hb crystallizes in the monoclinic system (and perhaps 

 also in the orthorhombic system). Foetal HbCO, HbO a and MetHb 

 crystallize in a system different from that of the adult derivatives, 

 probably triclinia Foetal Hb, like adult Hb, crystallizes in a system 

 different from that of the corresponding HbCO, HbO a and MetHb. 



The solubility data {Figures 9 and 10) given here do not suggest the 

 presence of more than one component in HbCO crystallized from 

 human adult blood. The variation in solubility of HbCO with ionic 

 strength of phosphate buffer pH 6-7 (Figure 10 curve 1) is linear and is 

 represented by Cohn's equation (log S = ft — K\ T / 2 ) for ionic strengths, 

 T / 2 = 4 — 6. This data agrees with that of Green, Cohn and Blanchard 7 . 

 The discontinuity at ionic strength about r / 2 = 5-5 in the corresponding 

 curve (phosphate pH 6-5) for human HbCO given by J. Roche, 

 Y. Derrien and M. Moutte 22 could not be confirmed in the present 

 work and may have been in part due to the formation of MetHb as 

 their experiment was carried out at 22°C. These preparations of 

 crystalline adult HbCO and HbO a also appear homogeneous by 

 electrophoresis 23 ' 14 and in the ultracentrifuge 24 . 



Amorphous human HbCO has been found here to be more soluble 

 than the crystalline material in potassium phosphate buffers at /?H 6-7 

 and 0°C. Roche, Derrien and Moutte 22 have compared the variations 

 in solubility with ionic strength for crystalline and amorphous HbCO 

 of horse, dog and pig in phosphate buffer, pH 6-5 and 22°C. In each 

 the amorphous preparation was more soluble than the crystalline. 

 In ammonium sulphate, also, the amorphous material (HbCO of 

 horse and rabbit) was more soluble than the crystalline, even after 

 estimating a correction for differences in their pH and temperature. 



276 



