Well, it turns out that if you react this molecule with our polypeptide and the alpha amino group does not have a positive charge, then this will react with it to basically form a bond. It will attach to this uncharged terminal alpha amino group. So if we draw the structure of our six amino acid polypeptide, this is what we get. So we have Alamine, we have arginine, we have phenylalanine, we have glycine, we have aspartate, and we have glycine. So this is the beginning and this is our end. So if this nitrogen is not charged, then the phenol isotherthionate will react with this and bind to it, and this will label it.