P. G. DERVICHIAN, G. FOURNET and A. GUINIER 



scattering curve appears practically the same as the curve obtained with 

 the untreated protein and gives again a gyration radius of 23 A (see 

 Figure 3). With haemocyanin, the presence of urea does not modify 

 the general shape of the scattering curve, but the hump is slightly dis- 

 placed as if the internal spacing was reduced to 170 A (by assuming 

 again the validity of Bragg's law). 



Figure 3. Variation of the scattered intensity 



with the angle of scattering. Haemoglobin with 



25 per cent urea 



IxlO 2x10 3x10 



Radian 



The negative result with haemoglobin is rather surprising since it 

 has been shown, particularly by J. Steinhardt 7 , that already at urea 

 concentrations of the same order of magnitude the haemoglobin 

 molecules are dissociated giving smaller sedimentation constants. It 

 would be interesting to reconcile these contradictory results obtained 

 on the one hand by measurements of sedimentation velocities and on 

 the other hand by our x-ray scattering analysis. The solutions studied 

 by Steinhardt contained only 0-43 to 0-65 per cent haemoglobin while 

 those we have submitted to the action of 25 per cent urea contained 

 from 3 to 12 per cent haemoglobin. The quantity of urea relative to 

 the quantity of protein may perhaps have an importance. 



Received September 1948 



REFERENCES 



1 Dervichian, D. G., Fournet, G. and Guinier, A. C. R. Acad. Sci., Paris 224 



(1947) 1848 



2 Kratky, O. /. PohmcrSc. 3 (1948) 195 



3 Guinier, A. Ann. Phys., Paris 12 (1939) 161 



4 Dervichian, D. G. /. Chim. phys. 38 (1941) 59 



(*) /. chem. Phys. 11 (1943) 236 



5 Boyes-Watson, J., Davidson, E. and Perutz, M. F. Proc. roy. Soc. A 191 



(1947) 83 



6 Polson, A. and Wyckoff, R. W. G. Nature, Lond. 160 (1947) 153 



7 Steinhardt, J. J. biol. Chem. 123 (1938) 543 



(*) For reasons indicated in the Editor's footnote, the translation of this article in 

 J. chem. Phys. had not been submitted to the author. Consequently the meaning of 

 some sentences has been obscured or modified. Other sentences express the reverse of the 

 idea found in the original text, e.g. title of Table I, where ' elongated ellipsoids ' should 

 read ' oblate ellipsoids'. 



134 



