Minimum structure of diapause hormone required for biological activity

Diapause hormone is a 24-amino acid peptide amide, and its C-terminal penta-peptide amide structure of FGPRL-NH2 is believed to be essential for biological activity. The penta-peptide amide, the shorter peptide amides, and their derivatives and analogs were prepared to determine the minimal structure for biological activity. The C-terminal amide group of the penta-peptide amide was not replaced with the other functional groups, but Gly, the 4th amino acid from the C terminal, could be substituted with an other amino acid while maintaining the biological activity. The shorter peptide amide, PRL-NR2, possessed low but significant activity, indicating the minimum structure of diapause hormone. By modifying its N-terminal, the aromatic ring of Phe is shown to enhance the activity of PRL-NH2.