Recent Developments in the X-Ray Study of Haemoglobin 



which has the same molecular weight as the adult one in concentrated 

 solutions — tends to split into quarter molecules in dilute solutions. 



Thanks to the courtesy of Dr. O'Brien and Mrs. Jope who are 

 supplying us with a variety of beautiful crystals, we have recently 

 embarked on a study of the human haemoglobin system. All the 

 crystals examined so far had complex structures with several molecules 

 in different orientations in the unit cell. The form studied in most 

 detail was carboxyhaemoglobin which forms beautiful orthorhombic 

 octahedra, but owing to the complexity of the intermolecular arrange- 

 ment the x-ray analysis yielded disappointingly meagre results 8 . In 

 the human haemoglobin system oxy-, carboxy- and methaemoglobin 

 crystals again seemed to form isomorphous crystals, while reduced 

 haemoglobin crystallized in two modifications which were both 

 different from the orthorhombic form of the other three derivatives. 

 (See this vol., p. 269.) Foetal human carboxyhaemoglobin forms 

 truncated rhombohedra which may be either mono- or triclinic and 

 are different from any crystals observed in the adult haemoglobin 

 system. 



CONCLUSION 



To the outside observer the effort that has to be spent on the x-ray 

 analysis of a crystalline protein may seem out of proportion to the 

 gain. Yet this method, though slow and laborious, still offers the only 

 way by which the molecular structure of the crystalline proteins can 

 be studied, and to date it has given us at any rate a glimpse of the 

 general layout of the polypeptide chains in two protein molecules, 

 some reasonably accurate data regarding their shape, and a number 

 of useful hints about the possible positions of the haems on the globin. 

 The haemoglobins are among the easiest proteins to crystallize. They 

 offer a wealth of crystalline compounds and derivatives, thus opening 

 a variety of different ways of approach to the problem of protein 

 structure. Some of these ways have proved dead ends, but many are 

 still leading on. 



Received September 1948 



REFERENCES 



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



(1947) 83 



2 Perutz, M. F. Proc. roy. Soc. A 195 (1949) 474 



3 — Trans. Faraday Soc. 425 (1946) 187 



* Astbury, W. T. Proc. roy. Soc. B 134 (1947) 303 

 5 Perutz, M. F. Nature, Lond. 143 (1939) 731 

 Haurowitz, F. Hoppe-Seyl.Z. 254(1938)266 



7 Kendrew, J. C. and Perutz, M. F. Proc. roy. Soc. A 194 (1948) 375 



8 Perutz, M. F. and Weisz. O. Nature, Lond. 160 (1947) 786 



147 



