ECDYSONE 20-HYDROXYLATION IN MANDUCA-SEXTA (LEPIDOPTERA, SPHINGIDAE) MIDGUT - DEVELOPMENT-RELATED CHANGES OF MITOCHONDRIAL AND MICROSOMAL ECDYSONE 20-MONOOXYGENASE ACTIVITIES IN THE 5TH LARVAL INSTAR

In the mid fifth-larval-instar tobacco hornworm, Manduca sexta, the mi dgut has high ecdysone 20-monooxygenase (E20MO) activity, with a peak at the onset of wandering on day five. Activities of E20MO, present bo th in mitochondria and in microsomes, were determined around the time of the peak. During the day preceding the peak the microsomal E20MO in creased 60-fold (total activity) or 115-fold (specific activity), and it decreased to one half or less of the peak activities within two day s after the peak. The mitochondrial E20MO increased only 1.3 to 2.4-fo ld (total and specific activities, respectively) before the peak, but declined more rapidly than the microsomal E20MO after the peak. It is concluded that mitochondrial and microsomal E20MO activities are contr olled independently and that changes in the physiological rate of ecdy sone 20-hydroxylation are effected primarily by changes of the microso mal E20MO activities.