PHYSICAL CHARACTERISTICS OF THE CEREBRAL BIG PROTHORACICOTROPIC HORMONE FROM MANDUCA-SEXTA

The prothoracicotropic hormones (PTTHs) are cerebral peptides that con trol insect postembryonic development by stimulating the prothoracic g lands to synthesize ecdysteroids. In Manduca sexta, the tobacco hornwo rm, 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 Stoke s radius of 2.59 nm and a sedimentation coefficient of 2.76 S. Based o n these data, an M(r) of 29,443.7 and an f/f(0), of 1.27 were calculat ed. Combined, the physical data reveal Manduca big PTTH is an asymmetr ical acidic homodimeric peptide with intra- and intermolecular disulfi de bonds.