Physical characteristics of the cerebral big prothoracicotropic hormone from Manduca sexta

The prothoracicotropic hormones (PTTHs) are cerebral peptides that control insect postembryonic development by stimulating the prothoracic glands to synthesize ecdysteroids. In Manduca sexta, the tobacco hornworm, two classes of PTTH are distinguished by their M(r), small (ca. 7 kDa) and big PTTH (ca. 25-30 kDa). Little is known about the physical nature of the PTTHs and this study takes a first step towards defining characteristics of the Manduca big PTTH. The neurohormone has a Stokes radius of 2.59 nm and a sedimentation coefficient of 2.76 S. Based on these data, an M(r) of 29,443.7 and an f/fo of 1.27 were calculated. Combined, the physical data reveal Manduca big PTTH is an asymmetrical acidic homodimeric peptide with intra- and intermolecular disulfide bonds.