9] CRYSTALLOGRAPHY OF MYOGLOBIN US 



Experience gained in preparing tiiis projection suggests tliat we shall in 

 most cases be able to determine phase angles within ±15-20°, We think 

 there is a good chance that a 6 Â. three-dimensional Fourier synthesis cal- 

 culated using such phases will reveal some recognizable features of the 

 structure. In any case such a synthesis is but a step towards the goal of 

 resolving individual atoms. We see no reason why the methods now being 



a sin /3 









X 10 



Fig. 7. Fourier projection of Type A myoglobin crystals along z, including all terms 

 of spacing greater than 6 Â 



used, or closely related ones, cannot be used at higher resolutions, although 

 the amount of work involved will in any case be considerable. Indeed, to 

 resolve individual atoms would mean measuring at least all the reflexions 

 with spacings exceeding 1-5 Â., that is to say 25,000 reflexions per crystal. 

 It would be premature to guess how far it may prove possible to carry the 

 analysis, although it seems certain that some extension beyond a resolution 

 of 6 Â. will be practicable. 



REFERENCES 



1. D. W. GREEN, V. M. INGRAM and M. F. PERUTZ, Proc. Roy. Soc, A 225, 287 



(1954). 



2. L. BRAGG and m. f. PERUTZ, Proc. Roy. Soc, A 225, 315 (1954). 



3. D. w. GREEN and A. c. T. NORTH. Unpublished data. 



4. G. BODO, H. M. DiNTZis and J. c. KENDREW. Unpublished data. 



5. H. scouLOUDi and j. c. kendrew. Unpublished data. 



6. D. MARKER, in Biological and Medical Physics, Vol. IV, Ed. J. H. Lawrence and 



C. A. Tobias, Academic Press, New York 1956. 



7. c. H. CARLISLE and J. D. BERNAL. Unpublished data. 



8. c. BOKHOVEN, J. c. SCHOONE and J. M. BIJVOET, Acta Cryst., 4, 275 (1951). 



9. R. PEPiNSKY and y. okaya, Proc. nat. Acad. Sei., Wash., 42, 286 (1956). 



