F. SANGER 



Composition 



Many analyses of insulin have been carried out with the 

 use of various methods, the most recent being that of Harfenist 

 (9), who used the chromatographic method of Moore and Stein. 

 These values are given in Table I. They agree well with the 

 values calculated from the structure (Figure 4), which was 

 determined largely by qualitative methods but which also made 

 use of the analytical values obtained by Chibnall and his co- 

 workers (see Tristram, ref. 24). These are also given in Table 

 I and differ only slightly from the more recent values. 



TABLE I 



Amino Acid Composition of Insulin 



Besides the 51 amino acid residues, crystalline insulin con- 

 tains a small amount of zinc (about one atom per 12,000 equiv- 

 alent weight), which is necessary for crystallization and appears 

 to be bound rather firmly, probably through the imidazole side 

 chains of the histidine residues (22). Whether or not it should 



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