Sequence of four amino acids at the end of the single polypeptide chain of lysozyme

During the investigation of DNP-lysozyme in which the end group of lysozyme was found to be lysine, a DNP-peptide (or peptides) was also isolated from certain hydrolysates. The fact that this DNP-peptide material yielded α,ε-di-DNP-lysine on complete hydrolysis lead to the conclusion that it is derived from the amino end of the lysosyme molecule. Further study has now been made of this peptide material and hydrolytic conditions have been found which cause DNP-lysozyme to yield some DNP-tetrapeptide as well as shorter DNP-peptides. Analysis of the tetrapeptide and of the smaller peptides has shown that the tetrapeptide has the composiition of α,ε-di-DNP-lysyl-valyl-phenylalanyl-glycine