Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 1995
Publication Date: N/A
Interpretive Summary: The development of insects is controlled by molting hormones. During the life cycle high molting hormone titers are required at certain times (molting, egg maturation) and low molting hormone titers at other times. This is accomplished in the insect by adjustment of the balance between hormone production and hormone inactivation. The present study is dealing with a vital enzyme for the production of the molting hormone. Without a sufficient quantity of this enzyme, molting and egg maturation would not be possible. The results showed that out of two similar enzymes found in the midgut of the tobacco hornworm, only one is essential for hormone production. This enzyme can now be targeted for the development of specific inhibitors, capable of blocking the growth and development of a variety of pest insect species and providing an alternative to pest control that is both more specific and less toxic than currently used insecticides.
The larval midgut of the tobacco hornworm, Manduca sexta, has high ecdysone 20-monooxygenase (E20M0) activity, located both in the mitochondria and in the microsomes. The apparent kinetic parameters for E20M0 in mitochondria and microsomes were determined. The Kms (for ecdysone) of the mitochondrial and microsomal enzymes were 1.63 x 10**-5 and 3.67 x 10**-7 M, respectively. The Vmax was 82.7 pmol/min/mg protein for mitochondria and 32.0 pmol/min/mg protein for microsomes. Although the mitochondrial E20M0 has the higher Vmax, at physiological ecdysone concentrations (10**-7 - 10**-8 M) it is only 1/8 to 1/10 as active as the microsomal enzyme. It is concluded that the microsomal E20M0 is the primary, if not the only enzyme involved in ecdysone 20-hydroxylation in M. sexta midgut.