Ecdysone 20-monooxygenase activity during larval-pupal development of Manduca sexta

Abstract

Profiles of ecdysone 20-monooxygenase (E-20-M) activity in the fat body and midgut of Manduca sexta were determined during larval-pupal development. The E-20-M activities for both tissues were found to exhibit a single major fluctuation during this 10-day period of development: fat body, a 10-fold fluctuation with peak activity on day 4; midgut, a 60-fold fluctuation with peak activity on day 5. Substrate kinetics revealed that the apparent K m values of fat body and midgut monooxygenases for ecdysone were fairly constant during the instar, 2.42 × 10 −7 M and 4.67 × 10 −7 M, respectively. By contrast, the monooxygenase V max values in each tissue fluctuated in a manner both quantitatively and temporally coincident with the fluctuations in enzyme activity. These findings suggest that changes in E-20-M activity are a function of changes in the titer of the enzyme. The possible developmental significance of the fluctuations in E-20-M activity are discussed.