This peptide corresponds to the protein transduction domain of the TAT protein and is synthesized with an activated cysteine residue C(Npys), wherein Npys is 3-Nitro-2-pyridinesulfenyl group and is used for activating S of cysteine and for rapid reaction when a thiol group is introduced. This kind of modification has been used to render this peptide as a cell penetrating and carrier peptide applicable in conjugation studies.