Tryptic digestion of peptides corresponding to modified fragments of human growth hormone-releasing hormone.

The objective of this study was to examine the degradation of short peptides corresponding to modified fragments of human growth hormone-releasing hormone by trypsin. Six analogues of pentapeptide 9-13 of human growth hormone-releasing hormone containing homoarginine, ornithine, glutamic acid, glycine, leucine or phenylalanine residue in position 11, two analogues of hexapeptide 8-13 of human growth hormone-releasing hormone and two analogues of heptapeptide 7-13 of human growth hormone-releasing hormone containing homoarginine or glycine residue in position 11 were obtained. The peptides were subjected to digestion by trypsin and the course of reaction was monitored using HPLC. It was found that the rate of hydrolysis of the Lys(12)-Val(13) peptide bond depends on the amino-acid residue preceding Lys(12). The extension of the peptide chain towards the N-terminus by introduction of consecutive amino-acid residues corresponding to the human growth hormone-releasing hormone sequence accelerates the hydrolysis process. These results may be of assistance in designing new analogues of human growth hormone-releasing hormone, more resistant to the activity of proteolytic enzymes.