On Determining the Chemical 

 Structure of Proteins 



WILLIAM H. STEIIN 



A decade ago an essay under this title would have seemed hopelessly 

 visionary. That it is not so today testifies to the precipitate progress 

 made in the intervening years by biochemistry in general and protein 

 chemistry in particular. Commencing with the introduction of chro- 

 matographic methods into amino acid chemistry by Martin and Synge, 

 this progress has culminated in the brilliant studies of Sanger (cf. 

 ref. 1 for references) that have revealed completely the arrangement 

 of the amino acid residues in the insulin molecule. Despite this strik- 

 ing success, determining the chemical structure of a protein is still far 

 from the routine procedure that will be necessary if proteins as a group 

 are to become susceptible to searching structural analysis. On the 

 basis of current knowledge, however, it is possible to formulate in some 

 detail the steps that will be required to determine the chemical struc- 

 ture of a protein. It is also possible to apprehend the nature of some 

 of the difficulties remaining, and, in a few cases, to suggest possible 

 methods by which they may be overcome. This essay will attempt 

 to discuss the problem from this point of view, using ribonuclease as a 

 specific example.* 



For the purposes of the present discussion, the determination of the 

 chemical structure of a protein will be limited to finding the sequence 

 of amino acids in the peptide chain (or chains), ascertaining the nature 

 and position of any cross linkages in the molecule, and determining 

 the manner of attachment to the peptide chains of any non- amino acid 



* The author owes much to the many fruitful and stimulating discussions he 

 has enjoyed with Dr. Stanford Moore and Dr. C. H. W. Hirs. It is particularly 

 fitting that, the studies on the structure of ribonuclease carried out by Dr. Hirs 

 form an important part of this essay, for he is a recent graduate of the Depart- 

 ment of Biochemistry at Columbia University. Permission to include this work. 

 some of it unpublished at the time of writing, is gratefully acknowledged. 



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