STRUCTURE OF INSULIN 



chromatography, hydrolyzed, and the amino acids identified. 

 The resuhs are shown in Table II. From the composition of 

 these peptides and the fact that peptide B4 on further partial 

 hydrolysis gives rise to the other smaller peptides (B2, B3) it is 

 clear that the A^-terminal sequence is Phe-Val-Asp-Glu. 



TABLE II 

 DNP-Phenylalanyl Peptides from Insulin 



When this work was carried out it was believed that the 

 molecular weight of insulin was 12,000 and that there were two 

 glycyl and two phenylalanyl chains. It was thus important to 

 know if the two phenylalanyl chains, for instance, were identical. 

 Evidence that this was so was obtained by a quantitative study 

 of the DNP peptides produced by partial hydrolysis of insulin ; 

 these yields are given in Table II, expressed as equivalents per 

 cent of the total terminal phenylalanine residues of insulin. The 

 three main peptides (B2, B3, B4) account for 59% and a further 

 20% is present in bands that give B4 on hydrolysis and must 

 therefore contain the same terminal sequence. Thus 92% of 



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