<scp>UV</scp> and <scp>IR</scp> spectroscopy of singly protonated <scp>DIYETDYYR</scp> , a tryptic peptide from the regulatory loop of insulin receptor

Abstract DIYETDYYR is a tryptic peptide from the regulatory loop of insulin receptor, which has the three tyrosine residues need for activation of the protein. In order to spectroscopically differentiate the tyrosine residues, singly protonated DIYETDYYR and its phenylalanine‐substituted analogs were studied by cryogenic ion spectroscopy. By comparing the UV absorption of the peptide at room temperature with those of phenylalanine‐substituted ones, the second and the third tyrosine residues showed UV absorption between 35 000 and 35 200 cm −1 , while the first tyrosine residue did not. Comparing the infrared (IR) spectra of the peptides at cryogenic temperature, the second tyrosine residue was found to have a hydrogen‐bonded phenolic OH. The IR spectra were explained by density‐functional‐based tight‐binding calculations. The structure of DIYETDYYR was tentatively assigned to the one with a hydrogen bond between the second tyrosine and the C‐terminus.