A Novel hGHRH Analog and its Comparative Activity

Growth hormone releasing hormone is one of the hormones secreted from the hypothalamus. Because of its potential applications in agriculture and medicine, its short half-life and its expensive chemical synthesis, an analog with high GHRH activity and prolonged half-life was sought after. The fusion partner gene with 127 amino acid residues of the C-terminus from L-asparaginase was recombined with asp-pro-hGHRH(1-44) gene synthesized by PCR method to form one kind of fusion protein with unique acid labile linker Asp-Pro. The Pro-hGHRH(1-44) peptide was purified to homogeneity by means of cell disruption, washing, ethanol precipitation, acid hydrolysis, SP-Sephadex C-25, and Sephadex G-10 column chromatography. The peptide's molecular weight of 5,139 Da as measured by EIS-MS was coincident with the actual values. In the study of the activity, the doses of peptide were 0.1, 1.0, and 10 g/μl for rat pituitary and 5 g/μl for human pituitary. The peptide increased GH releases from rat pituitary in a concentrationdependent manner (P<0.05; P<0.01). At 1.0 g/ml, there was a significant difference between Pro-Pro-hGHRH(1-44)- Gly-Gly-Cys and Pro-hGHRH(1-44) or Pro-Pro-hGHRH(1-44) (P<0.05), whereas the standard hGHRH(1-40) showed no measured rGH release. For human fetal pituitary, the Pro-hGHRH(1-44) peptides showed good GH-releasing activity, but there were no significant differences between them. The structure-activity relationship showed that for both rat and human fetal pituitary, the net GH-releasing activity of the Pro-hGHRH(1-44) analog was more than that of Pro-Pro-hGHRH(1- 44). The results of the other hormones from human pituitary showed that the analog had good function-selectivity and species specificity.