Tryptic hydrolysis of hGH-RH(1-29)-NH2 analogues containing Lys or Orn in positions 12 and 21.

Two analogues of the 29 amino acid sequence of human growth hormone-releasing hormone, namely [Nle27]hGH-RH(1-29)-NH2 and [Orn(12,21),Nle27]hGH-RH(1-29)-NH2, have been synthesized and subjected to digestion by trypsin. The course of degradation was followed using RP-HPLC and ESI-MS. Several intermediates and final products of degradation were identified and conclusions regarding the rate of cleavages at different positions occupied by Lys and Arg residues were drawn. The analogue containing ornithine was found to be less susceptible to hydrolysis by trypsin: the 12-13 and 21-22 peptide bonds were completely resistant to the cleavage. The results show that by replacing Lys with Orn, a possibility exists to design new peptides, which could be more stable in biological fluids.