Insect Diapause, its Chemical Control and Elucidation of Molecular Mechanism

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To determine the structure-activity relationships of diapause hormone of the silkworm, Bombyx mori, a series of peptide analogs having different chain length starting from the parent C-termunus an analogs having free acid C-terminal were chemically synthesized by solid-phase Fmoc methodology and were further purified by HPLC.Bioassay elicited the non-active nature of the free acid C-termunus and the retained activity of those shorter chain with the amidated C-termunal analogs among which the response depended on the length of the chain. It means that the active peptides required two minimal elements, namely the sequence near and the amidation of the C-termunus. The amidated C-termunus did not show better protective role against enzymatic digestion in pupal and larval haemolymph than the free acid C-termunal analog. This suggested its involvement in the existence of a certain higher order structure needed in expression of biological activity. Moreover, as most of the hydrophobic amino acids locate close to the C-termunal portion, the sequence near that terminus could be alternatively related to the necessary hydrophobicity. Consequently, both the hydrophobicity of the portion near and the amidation of the C-termunus were indispensable structure for diapause hormone activity.