Before the purification the peptides were dissolved in H2O, DTT was added (6-fold excess with respect to purified peptide) and the mixture was sonified for 30 min in 60°C. Purification of the crude peptide was carried out by using RP-HPLC on a semi-preparative Phenomenex Luna C8(2) (250 mm x 20 mm, 5 μm) column. A linear gradient from 5% B to 50% B in A in 150 min was used. The aqueous system (A) consisted of 0.1% (v/v) TFA solution in water, whereas the organic phase (B) was 80% acetonitrile in water, containing 0.08% (v/v) TFA. Purification was monitored by UV absorption at a wavelength of 222 and 254 nm. The purity of the peptide was verified by LC-ESI-IT-TOF/MS (Shimadzu, Shimpol, Warsaw, Poland), and by using RP-HPLC with a Kromasil C8 analytical column (250mm x 4.6 mm, 5 μm), where a gradient of 5% to 100% B in A in 60 min was employed, with A and B as described above.