High affinity juvenile hormone binding protein of the haemolymph of the southwestern corn borer, Diatraea grandiosella: Characteristics and relation to diapause

Abstract

The juvenile hormone (JH) binding activity of the plasma of pre-diapausing and diapausing larvae of the southwestern corn borer, Diatraea grandiosella, was examined. The source of the high affinity JH binding protein was investigated, and the protein was purified and partially characterized. The total JH binding activity for JH-I and JH-III increased in the plasma of pre-diapausing larvae, reached a plateau at the beginning of diapause, and remained relatively high throughout diapause. Neither the total JH binding activity nor the activity of the high affinity JH binding protein appeared to be related to the JH titre present in the plasma. The fat body of pre-diapausing, early diapausing, and mid-diapausing larvae was found to release a high affinity JH binding protein when it was incubated in vitro in Grace's medium. The maintenance of the relatively high levels of high affinity JH binding protein in the plasma of diapausing larvae may, therefore, depend upon the continued synthesis and release of the protein from the fat body. The high affinity JH binding protein present in the plasma of diapausing larvae was purified using gel filtration, ion exchange chromatography, isoelectric focusing and electrophoresis. The purified protein was subjected to denaturing electrophoresis and found to consist of a single polypeptide chain with an apparent molecular weight of about 30,000, and to exhibit a dissociation constant of 4.6 × 10 −7 M at 4°C for JH-I.