The terminal peptides of insulin

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Abstract
The dinitrophenyl method for the identification of the terminal residues of proteins has been extended by the use of partial hydrolysis to the identification and estimation of terminal peptides. The method was applied to insulin; and it was shown that both the terminal phenylalanyl residues are present in the form of the tetrapeptide sequence phenylalanyl-valyl-aspartyl-glutamic acid, both the lysyl residues which are in the same chains are present in the sequence threonyl-prolyl-lysyl-alanine and both the terminal glycyl residues are present in the penta-peptide sequence glycyl-valyl-glutamyl-glutamic acid. It is concluded that the insulin molecule is built up of 2 pairs of very similar, if not identical, polypeptide chains.