PTTH is a brain secretory polypeptide of insects which stimulates the prothoracic glands to produce and release ecdysone, the steroid essential to insect development. Peptides P2K and P6K are presumed to be cleaved post-translationally and may play some unknown physiologically or developmentally important functions. Homodimer; disulfide-linked. PTTH is synthesized by two dorsolateral neurosecretory cells of the Bombyx brain.